Hadron 2015

Sunday, September 13, 2015

Tuesday, September 15, 2015

Plenary Session - 8:30 - 12:30                                                        Grand Ballroom II

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  • An overview of recent theoretical ideas concerning the X,Y, Z exotic states is presented.
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  • Hadron spectroscopy is a unique way to access QCD, which is one of the most important physics goals of BESIII. BESIII brings great opportunities to study the XYZ states of charmonium by directly producing the Y states up to 4.6 GeV. High statistics of charmonium decays collected at BESIII provide an excellent place for hunting glue balls and studying the excited baryons. Recent results of light hadron spectroscopy and charmonium spectroscopy from BESIII will be reported.
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  • We present recent BaBar results on the searches for new physics. This includes searches for dark photons,  light Higgs resonances, and new long lived neutral particles. We will also show the implication that our result on the dark photon search has for the difference between the calculated and measured anomalously magnetic moment of the muon. In addition, we report on the first observation of CP-Violation in B0bar->D(*)_CP h0 decays using a combined time-dependent analysis of  the BaBar and Belle  data.
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  • The understanding of the structure of the Λ(1405) resonance has been one of the central issues in hadron physics. In this talk, we discuss the pole position in the scattering amplitude and the internal structure of the Λ(1405). We first review the recent study of the Λ(1405) based on the coupled-channel approach for the meson-baryon scattering with next-to-leading order chiral interaction. It is emphasized that the precise determination of the kaonic hydrogen and the comprehensive measurements of the pi Sigma mass spectrum in various production reactions are crucial to constrain the scattering amplitude. It is shown that the uncertainty in the pole structure is significantly reduced thanks to the theoretical and experimental developments. We then discuss the internal structure of the Λ(1405). We will show that the Kbar N molecule picture of the Λ(1405) is supported by the analysis of the compositeness and the wave function from the Kbar N potential.
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  • The LHCb experiment recently discovered two pentaquark-charmonium states, P_c⁺ (4450) and P_c⁺(4380), in the amplitude analysis of the Λ_b⁰ to J/psi p K- decays. The data sample used in this analysis is collected by the LHCb detector from the 7 and 8 TeV pp collisions at the LHC, corresponding to an integrated luminosity of 3 fb-1. Through the amplitude fits the mass and the width of each exotic resonance are determined. The significance of each resonance is above 9 standard deviations. The fits also provide information on the J^P quantum numbers. The preferred results are that one state has spin 3/2 and the other 5/2 and that the two states have opposite parity.
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Parallel Sessions - 2:00 - 3:45

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  • Recent calculations of light meson scattering will be presented. Several advances have made it possible to extract coupled-channel hadron-hadron scattering amplitudes in a systematically improvable way using lattice QCD. The methods used in some of these first calculations will be explained in detail, and specific applications will be described. I will focus on channels involving pairs of π, K, η,η’ mesons. Finite volume energy levels describing these systems are obtained from large correlation matrices that are then diagonalized using the variational method to obtain a spectrum. These finite volume spectra are then used to constrain infinite volume scattering amplitudes that may in turn be analyzed for their pole content to extract resonance properties.
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  • I will discuss some recent investigations of excited mesons using first-principles calculations in lattice QCD. We have made significant advances in studying near-threshold states, resonances and related scattering phenomena over the last few years. I will illustrate this progress by presenting results from scattering channels involving charm mesons, including D K scattering relevant for the enigmatic D_s(2317). I will also comment on applications to other channels and future prospects.
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  • We study the interaction of the ρ and D^*Dbar^* with spins aligned using the Fixed Center Approximation to the Faddeev equations. We select a cluster of D^*Dbar^*, which is found to be bound in I=0 and can be associated to the X(3915), and let the ρ meson orbit around the D^* and Dbar^*. In this case we find an I=1 state with mass around 4340 MeV and narrow width of about 50 MeV. We also investigate the case with a cluster of ρD^* and let the orbit around the system of the two states. The ρD^* cluster is also found to bind and leads to the D^*2(2460) state. The addition of the extra Dbar^* produces further binding and we find, with admitted uncertainties, a state of I=0 around 4000 MeV, and a less bound narrow state with I=1 around 4200 MeV.
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  • The BESIII Experiment at the Beijing Electron Positron Collider (BEPC2) collected large data samples for electron-positron collisions with center-of-mass above 4 GeV during 2013 and 2014.  In this mass region, there are several states that are yet to be understood. In this talk we will discuss BESIII analyses of the tetraquark candidate Z_c states. We will present the studies of their decays to hidden charm and open charm final states for both the charged and neutral Z_c's.  In addition, a PWA of the Z_c(3900) will be reported.
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  • In the conventional quark model, mesons are composed of one quark and one anti-quark, while baryons are composed of three quarks [1]. However, exotic hadronic states with other configurations have been searched for and many candidates were proposed [2, 3]. These states include glue balls (with no quark), hybrids (with quarks and excited gluon), multi-quark states (with more than three quarks), and hadron molecules (bound state of two or more hadrons).  Dramatic progress was made in the study of the exotic states after the running of the two B-factories, i.e., Belle at KEK and BaBar at SLAC. Since the discovery of the X(3872), lots of new states (called charmonium-like/bottomonium-like states or XY Z particles) have been observed [3, 4, 5, 6].
    In my report, I present the most recent results on the study of the XY Z states from Belle experiment. Meanwhile, I also show some possible theoretical explanations for them. My report can be divided into four parts: (1) We search for the X(3872)-like state (named X_b) decaying into ωϒ (1S) using a 118 fb^-1 data sample acquired with the Belle detector at a center-of-mass energy of 10.867 GeV [7]; (2) We update measurements of the cross sections of e⁺e^- →π ⁺π ^-J/ψ and π ⁺π ^-y(2S) via ISR method using a 980 fb^-1 data sample. The properties of the Y(4008), Y (4260), Y(4360) and Y(4660) states are updated [8, 9]; (3) Charged charmonium-like state Z_c(3900) and Z_c(4200) are observed in e⁺e^-→π ⁺π ^-J/ψ [8] and Bbar⁰→ J/ψ K^-π⁺ [10]. Evidence for a charged charmonium-like structure at 4.05 GeV/c2 is observed in the π±ψ(2S) mass spectrum from the Y(4360) decays [9]. A strange partner of the Z_c(3900) ±, called Z_cs, is also searched for in K±J/ψ system in e⁺e^-→K⁺K^-J/ψ [11]; (4) The prospects for the study of the XY Z states in the future at Belle II.
    

    References:
    [1]  M. Gell-Mann, Phys. Lett. 8, 214 (1964)
    [2]  E. Klempt and A. Zaitsev, Phys. Rept. 454, 1 (2007)

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  • The existence of the X(3872) suggests the presence of
    bottomonium counterpart. Search for X_b with the ATLAS experiment in the final state of Upsilon ππ is presented.
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  • We present a plausible mechanism for the origin of the XY Z mesons in the heavy meson spectra within a standard quark-model picture [1, 2, 3]. We discuss the conditions required for the existence of four–quark bound states or resonances contributing to the heavy meson spectra, being either compact or molecular. We concentrate on charmonium and bottomonium spectra, where several new states, difficult to understand as simple quark-antiquark pairs, have been reported by different experimental collaborations. The pivotal role played by entangled meson-meson thresholds is emphasized.
    

    References:
    [1]  J. Vijande and A. Valcarce, Phys. Lett. B 736, 325 (2014)
    [2]  T. F. Caramés, A. Valcarce, and J. Vijande, Phys. Lett. B 709, 358 (2012)
    [3]  T. Fern´andez-Caramés, A. Valcarce and J. Vijande, Phys. Rev. Lett.

                103, 222001 (2009)
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  • We propose a new measurement of the proton Zemach radius, which is the first moment of the convolution of the proton charge and magnetic moment distributions. We determine the Zemach radius from the ground-state hyperfine splitting energy of muonic hydrogen. Studies of the proton electromagnetic structure has recently attracted great interest stimulated by the proton radius puzzle. It is a significant inconsistency in the proton charge radius between the electronic and muonic determination methods. Since the proton charge radius is defined only from the electronic distribution in the proton, it is a curious question as to how we can determine the magnetic distribution in the proton probed with muons. A precise determination of the proton Zemach radius may provide a crucial insight into the proton radius puzzle. To determine the hyperfine splitting energy of the ground-state muonic hydrogen, we use the decay asymmetry of the spin-polarized muons induced by a circularly-polarized laser. We identify the resonance frequency corresponding to the hyperfine splitting energy by detection of the spatial distribution of decay electrons during the frequency scan. In this contribution, we present the physics motivation, the experimental principle and its feasibility.
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  • New data points to high momentum nucleons in the nucleus as the cause of the EMC effect. These high momentum initial-states are not only found in heavy nuclei but also in the loosely bound deuteron. This implies that both the numerator and denominator in the EMC effect ratio is important. The current status of the data along with an overview of upcoming experiments will be reviewed.
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  • Transition Distribution Amplitudes (TDAs) are parametrizations of the hadronic matrix elements that occur in the perturbative Quantum ChromoDynamics calculations of a certain family of reactions within framework of collinear factorization. This framework has had significant success in the analysis of Deeply Virtual Compton Scatterings where Generalized Parton Distributions are the relevant confinement related hadronic matrix elements. There has been interest within the theoretical community to replicate the success to other families of reactions, in particular backward Virtual Compton Scattering and backward meson electro-production, and more recently, the related reaction of J/ψ production with an associated meson in pρbar annihilation. The universality of the TDAs for these reactions and the validity of the factorization approach have not been proven yet, but constitute a promising avenue for current and future experiments to extend our understanding of the reaction mechanisms. Indeed the measurement of a variety of reactions covering as wide a range in kinematic coverage as possible is crucial ingredient for the validation of the approach in these reactions.
    The PANDA experiment under preparation at the future FAIR facility will be ideally suited to access these observables, in particular the pion-to-nucleon TDAs (πN TDAs) which can be used to learn about the pion cloud contribution in the nucleon wave function. The factorization approach requires the existence of a large scale q², which is provided by the large mass of the J/ψ. The wide kinematic coverage of the PANDA detector will be crucial in testing the predictions of the momentum transfer dependence of the cross-section by specific calculations. It is in this context that we propose a complete feasibility study of the measurement of one of the reactions covered by the TDA models pρbar → π⁰ J/ψ with the J/ψ decaying in the e⁺e^- channel. Our signal cross sections are based on estimations by [1] and we consider the main background contributions, including the reaction pρbar → π⁰π⁺π^- which has a cross-section larger by at least 7 orders of magnitude in some kinematic regions. The existing data on these reactions is weak, but provides to anchor the integrated cross-section, whereas for the shapes we rely on model predictions. We demonstrate that this reaction is readily measurable by PANDA and provide estimates for the counting rates and signal to background for typical luminosities that will be available.

    [1] B. Pire, K. Semenov-Tian-Stansky, and L. Szymanowski. Nucleon-to-pion transition distribution amplitudes: A challenge for PANDA. Few-Body Systems, 55(5-7):351{356, 2014.

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  • The very first Run II LHC data allows LHCb to measure the cross-sections for quarkonia, beauty and charm productions. Results should be available quickly thanks to the new "Turbo" stream procedure allowing the analysis of particle candidates selected at trigger level without the need of offline reconstruction. First results are presented, conditional on LHC machine operation.
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Parallel Sessions - 4:15 - 6:00

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  • Results are reported on spectroscopy and properties of various light-quark mesons studied in untagged two-photon collisions with the Belle detector. Also discussed are single-tag two-photon studies of the π⁰ and π⁰π⁰ formation. The investigated mass region is from 0.9 to 2.6 GeV.
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  • Recent results from the SND detector obtained in experiments at the VEPP-2000 e⁺e^- collider are presented. The reactions e⁺e^- to η π⁺π^-, e⁺e^- to K⁺K^-, e⁺e^- → π⁺π^-π⁰, ω π⁰, ωη have been studied in the energy region 1.05-2.00 GeV. The neutron and proton electromagnetic form factors has been measured in the energy range from the threshold up to 2 GeV. The result of the search of the rare process e⁺e^- → η' is also presented.
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  • The combined data of cross section of the process, e⁺e^- → π⁺π^-π⁰ obtained by SND and BABAR in the energy region sqrt{s} below 2 GeV are re-analyzed to study excited omega states in the energy region sqrt{s} between 1 GeV and 2 GeV. A relative phase between ω and φ amplitudes, Θ_ωφ, was taken below 180 degrees in the SND works. In the present work, we carefully searched for the solution not only below 180 degrees of Θ_ωφ, but also above 180 degrees. We have obtained solutions for mass and width values of two excited w states, one around 1,200 MeV and around 700 MeV, the other around 1,600 MeV and around 125 MeV in the region Θ_ωφ above 180 degrees. The former seems to be different from ω(1420) described in the PDG tables. We will report the results of our analysis in details.
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  • The study of η-decays allows the probing of symmetry-breaking phenomena, to test theoretical calculations and to explore the anomalous sector of QCD. In order to perform those studies two data samples have been acquired with the WASA-at-COSY facility at Forschungszentrum Juelich, Germany. A proton beam is accelerated within the COSY storage ring towards a liquid deuterium or a liquid hydrogen pellet target producing η-mesons via: pd → ³Heη or pp → ppη. The η-decay products as well as the forward-scattered projectiles are detected within the 4π WASA-at-COSY detector.
    A first round of experiments was done with the pd → ³Heη reaction used for the study of the more abundant η decay channels such as η → π⁺π^-π⁰ or η → π⁺π^-γ and to set up the framework for a common analysis. In order to address the rare η-decays (e.g.η → e⁺e^-e⁺e^-) a high-statistics data set has been collected in the reaction pp → ppη.  This talk will give an overview of the status of the analyses of the two data sets.
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  • As lattice QCD calculations continue to improve, scattering observables are becoming available. The Hadron Spectrum collaboration recently calculated the pion-pion spectrum in the rho channel with quark masses that yield a 240 MeV pion. Using Luscher's method, this finite volume spectrum can be used to extract the infinite volume phase shift. The resonant behavior is clearly evident when the phase shift is fit to a Breit-Wigner. This is not the end of the story, though! Having performed the calculation at unphysically-large quark masses, connection with experimental results requires further analysis. We present our use of Unitarized Chiral Perturbation Theory to connect the Hadron Spectrum calculation with experimental results. We find that this chiral extrapolation does an excellent job reproducing experimental pion-pion scattering data.
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  • The BaBar Collaboration has an intensive program studying hadronic cross sections at low-energy e⁺e^- annihilations, accessible via initial-state radiation. These measurements allow significant improvements in the precision of the predicted value of the muon anomalous magnetic moment. We report here the results of recent studies of a number of final states, such as  e⁺e^- → K⁺K^-, e⁺e^- → K⁰_S K⁰_L , e⁺e^- → K⁰_S K⁺ π^- π⁰ and e⁺e^- → 4 pions.
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  • We report cross section measurement of e⁺e^- → ppbar  at 12 c.m. energies in the range of 2232.4 to 3671.0 MeV using BESIII data. The electromagnetic form factor of the proton is deduced by assuming electric and magnetic form factor to be equal (|G_E| = |G_M|), and the ratio of electric to magnetic form factor, |G_E|/|G_M|, and |G_M| are extracted by fitting the distribution of the polar angle of the proton at 3 energies. Using a data sample of 2.9/fb taken at a center-of-mass energy of 3.773 GeV with the BESIII detector, the e⁺e_- → π⁺π^- cross section in the energy range between 600 MeV and 900 MeV is extracted using the method of Initial State Radiation (ISR). The cross section is measured with a systematic uncertainty around 1.4%. The pion form factor |F_π|² is also extracted and is expected to contribute to the hadronic vacuum polarization of (g-2)μ.
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  • We make predictions for the ratios of branching fractions of Bbar and Bbar_S⁰ decays into J/ψ and the scalar mesons f₀(1370), f₀(1710), or tensor mesons f₂(1270), f'₂(1525), K₂^*(1430). The theoretical approach is based on results of chiral unitary theory where these resonances are shown to be generated from the vector meson-vector meson interaction. Eight independent ratios can be predicted and comparison is made with the recent data on Bbar^S₀ decay into J/ψ f'’₂(1525) versus the Bbar_S⁰ decay into J/ψ f₂(1270). Phys.Rev.D90 (2014) 9, 094006
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  • The talk is mainly based on the work of arXiv:1503.02463 [hep-ph]. Based on our previous studies that support the important role of the f₂(1270), f₂(1525), and Kbar₂^*(1430) resonances in the J/ψ[ψ(2S)] → Φ(ω)VV decays, we make an analysis of the analogous decays of ϒ(1S) and ϒ(2S), taking into account recent experimental data. In addition, we study the J/ψ and ψ(2S) radiative decays and we also made predictions for the radiative decay of ϒ(1S) and ϒ(2S) into
    γf₂(1270) γf₂'(1525), γf₀(1370) and γf₀(1710), comparing with the recent results Phys.Rev.D 91,052006 (2015) of a CLEO experiment. We can compare our results for ratios of decay rates with eight experimental ratios and find agreement in all but one case, where experimental problems are discussed.
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  • We extend a recent approach to describe the B⁰ and B⁰_s decays into J/ψ f₀(500) and J/Ψ f₀(980), relating it to the B₀ and B⁰_s decays into J/Ψ  and a vector meson, ω, ρ,  K^*. In addition, the B⁰ and B⁰_s decays into J/ω and _κ(800) are evaluated and compared to the K^* vector production. The rates obtained are in agreement with the available experiment while predictions are made for the J/ψ plus κ(800) decay.
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  • I will discuss the role of the anomalous triangle singularity (ATS) in the production of open threshold states in both light and heavy quark sector. I will demonstrate that the ATS is a rather general and useful for a systematic understanding of the nature of some of those “XYZ” states in the heavy quark sector and disentangling some old puzzles such as the nature of η(1405) and η(1475),  and the long-standing  “ρπ puzzle” and non-DDbar decay of Ψ(3770).
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  • The present day experimental data on the X(3872) decays do not allow to make clear conclusions on the dominating structure of this state. We propose an alternative way to study the structure of X(3872) by means of the two-step Dbar^* (or D) production in pbarA reactions [1]. On the first step, the antiproton collides with a bound proton of the nuclear target and forms the X-state on the mass shell, pbarp → X. On the second step, the formed X – assumed to be the mixture of the D⁰Dbar^*0 + c.c. and D⁺D^*− + c.c. molecular states – experiences the stripping reaction XN → Dbar^*(D)(+anything) on another bound nucleon. Such a two-step process leads to the characteristic narrow peaks of the Dbar^* (or D) distributions in the light cone momentum fraction
    
    α = 2 (ω+k^z)/(E_^-p+m_N+p_lab)
    
    where k and ω = (k² + m²_D(*))^1/2 are, respectively, the meson momentum and energy in the laboratory frame, close to α ≅ 1 at small transverse momenta. Other models, like tetraquark, gluon hybrid, or hadro-quarkonium, where the primordial hadronic components are absent in X(3872), would result in the flat α-distributions of produced Dbar^* (or D). Thus, the narrow peaks of Dbar^*(D) production at α ≅ 1 at small k_t can be used to test the hypothetical DDbar^* +c.c. molecular structure of X(3872). A similar approach can be also applied to study the possible exotic molecular structures of the other hadrons, including other X, Y,Z states, light mesons a₀(980) and f₀(980), D_S^*0(2317) and D_s1(2460) states, and Λ(1405) hyperon.
    
    

    Reference: [1] A. Larionov, M. Strikman, M. Bleicher, (2015), arXiv:1502.03311 [nucl-th]

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  • Since the discovery of the X(3872) the study of heavy meson molecules has been the subject of many investigations. On the experimental side different experiments have looked for his spin partners and the bottom analogs. On the theoretical side different approaches have been used to understand this state. Some of them are EFT that impose HQSS and so they make predictions for the partners of the X(3872), suggesting the existence of a J^PC = 2⁺⁺ partner in the charm sector or J^PC = 1⁺⁺ or 2⁺⁺ analogs in the bottom.
    In our work, in order to understand the X(3872), we use a Chiral quark model in which, due to the proximity to the DD* threshold, we include ccbar states coupled to DD* molecular components. In this coupled channel model the relative position of the bare ccbar states with two meson thresholds are very important. We have looked for the X(3872) partners and we do not find a bound state in the D*D* J^PC = 2⁺⁺. In the bottom sector we find the opposite situation where the B*B* with J^PC = 2⁺⁺ is bounded while the J^PC = 1⁺⁺ is not bounded.
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• (Abstract |
  • We consider the X(3872) resonance as a J^PC = 1⁺⁺ DDbar^*  hadronic molecule. According to heavy quark spin symmetry, there will exist a partner with quantum numbers 2⁺⁺, X₂, which would be a D^*Dbar^* loosely bound state. The X2 is expected to decay dominantly into Dbar, DDbar^* and  in d-wave. In this work, we calculate the decay widths of the X₂ resonance into the above channels, as well as those of its bottom partner, X_b2, the mass of which comes from assuming heavy flavor symmetry for the contact terms. We find partial widths of the X₂ and X_b2 of the order of a few MeV. Finally, we also study the radiative X₂ →DbarD^* _ϒ and X_b2 → Υ decays. These decay modes are more sensitive to the long-distance structure of the resonances and to the DbarD^* or BbarB^*  final state interaction.
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Wednesday, September 16, 2015

Plenary Session - 8:30 - 12:30                                                        Grand Ballroom II

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  • We illustrate the need and the advantages of a multi-dimensional exploration of the structure of the nucleon, and in general of hadrons. We introduce new tools, like the Generalized Parton Distributions (GPDs) and the Transverse Momentum Distributions (TMDs), which enable us to explore the dynamics of partons beyond the usual collinear approximation adopted in the QCD analysis of hard processes. We emphasize the possibility of using these tools to address the (orbital) angular momentum of partons, and to contribute to solving the puzzle on the partonic decomposition of the Nucleon spin. We highlight recent preliminary results on TMDs extraction as a first step towards a general setup for global fits, similarly to what was done for ordinary collinear parton distributions. We briefly touch on the possible breaking of universality for a specific category of polarized TMDs; as an example, we describe the Sivers effect as a fundamental test of our understanding of the color force in QCD.
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• (Abstract |
  • COMPASS is a fixed target experiment at the CERN SPS M2 beam line, taking data since year 2002. Part of its physics program is dedicated to study the longitudinal and the transverse spin and the transverse momentum structure of the nucleon using semi- inclusive deeply inelastic lepton scattering (SIDIS). For these measurements, data have been collected using longitudinally and  transversely polarized proton (NH3) and deuteron (⁶LiD) targets. A selection of recent results is presented and discussed.
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  • We present recent results from the Mainz Microtron MAMI, which is a high intensity electron accelerator with (polarized) beam energies up to 1.6 GeV. Currently, two major experiments are operated at MAMI. The A1 spectrometer setup is ideally suited for high-resolution electron scattering experiments, which allows for world class results e.g. in the fields of electromagnetic form factor measurements – related to the proton radius puzzle – as well as dark photon searches. The second experiments is the Crystal Ball/TAPS calorimeter setup (A2 collaboration), which is operated at the tagged photon beam facility and is suited for photo production experiments with the goal to determine precisely the baryon spectrum in the low-energy region. A polarized target for longitudinal and transversal beam polarization in combination with the polarized beam does not only allow for experiments in the field of baryon spectroscopy, but also opens the avenue for investigations of the polarizabilities of the nucleons, for which new results are presented. In addition, the extremely high rate of pseudoscalar mesons, which are produced at MAMI in a clean electromagnetic environment, allows for measurements of meson decays as motivated by precision tests of chiral perturbation theory or precision tests of the Standard Model. At the end of the talk we will also outline the opportunities at the accelerator MESA (Mainz Energy-Recovering Superconducting Accelerator), which is currently under construction in Mainz, and for which a  low-Q² measurement of the weak charge of the proton is foreseen as one of the flagship experiments of the new facility.
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  • I will describe the use of finite-volume methods in the extraction of hadron scattering amplitudes from first-principles QCD calculations. Using lattice QCD to determine the discrete spectrum of states in a box, we are able to map out the energy dependence of amplitudes and to examine their resonant content. I will illustrate the progress made in recent years in the elastic scattering problem using the example of the ρ-resonance in ππ scattering. The first determination of a coupled-channel scattering matrix within QCD, considering the πK, ηK system, will be presented along with a discussion of the K* resonant content of the amplitudes. Extensions of this work to other coupled systems, and to scattering systems featuring external currents, will be discussed.
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• (Abstract |
  • The goal of the COMPASS experiment at CERN is to study the structure and dynamics of hadrons. The two-stage spectrometer has a good acceptance over a wide kinematic range for charged as well as neutral particles and thus allows access to a wide range of reactions. Light mesons are studied with negative (mostly π^-) and positive (p, π⁺) hadron beams with a momentum of 190 GeV/c.
    The spectrum of light mesons is investigated in various final states produced in diffractive dissociation reactions at squared four-momentum transfers to the target between 0.1 and 1.0 (GeV=c)². The flagship channel is the π^-π⁺π^- final state, for which COMPASS has recorded the currently world's largest data sample. These data not only allow to measure the properties of known resonances with high precision, but also to search for new states. Among these is a new axial-vector meson, the a₁(1420), with unusual properties. Novel analysis techniques have been developed to extract also the amplitude of the π^+-π^- sub-system as a function of 3π mass from the data. The findings are confirmed by the analysis of the π^-π⁰π⁰ final state. Further insight is gained by studying diffractively produced channels with η or η' in the final state or centrally produced systems. The radiative coupling of light mesons is studied in pion-photon scattering, which is embedded into Primakoff reactions on nuclear targets at lowest four-momentum transfers.
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Thursday, September 17, 2015

Parallel Sessions - 8:30 - 10:15

• (Abstract |
  • COMPASS is a fixed-target experiment at the CERN SPS, which focuses on light-quark hadron spectroscopy. It collected a large dataset using a 190 GeV/c hadron beam impinging on a liquid-hydrogen target in order to study, inter alia, the central exclusive production of scalar light mesons. The goal is to search for so-called glue balls, which are hypothetical meson-like objects without valence quark content.
    We present results, where we selected centrally produced pion or kaon pairs in the final state from the COMPASS proton-beam dataset. The angular distributions of the two pseudo-scalars in the final state are decomposed in terms of partial waves, where particular attention is paid to the inherent mathematical ambiguities. The large dataset allows us to perform a detailed analysis in bins of the two squared four-momentum transfers carried by the exchange particles in the reaction. Possible parameterizations of the mass dependence of the partial-wave amplitudes in terms of resonances are studied.
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• (Abstract |
  • We investigate the decay of f₁(1285) → KKbar π with the assumption that the f₁(1285) is dynamically generated from the KK*bar interaction. In addition to the tree level diagrams, we take into account also the final state interactions. The partial decay width and mass distributions of f₁(1285) → πKKbar are evaluated. We get a value for the partial decay width which, within errors, is in fair agreement with the experimental result. The contribution from the tree level diagrams is dominant, but the final state interactions have effects in the mass distributions. The predicted mass distributions are significantly different from phase space and tied to the KK*bar nature of the f₁(1285) state.
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• (Abstract |
  • We evaluate the decay width for the processes f₁(1285) → πa₀(980) and f₁(1285) → πf₀(980) taking into account that all three resonances are dynamically generated from the meson-meson interaction. We use a triangle mechanism which provides a decay width for f₁(1285) → πa₀(980) with a branching fraction of the order of 30%, in agreement with experiment. At the same time we evaluate the decay width for the isospin forbidden f₁(1285) → πf₀(980), which arise when we consider different masses for the charged and neutral kaons.
• | Presentation)

• (Abstract |
  • Measurement of the polarization observable E used circularly polarized photons at center of mass energies between 1450 MeV and 2050 MeV in Hall B at the Thomas Jefferson National Accelerator Facility. The target used in this experiment was butanol. Two different electron beam energies, 1.465 GeV and 2.478 GeV, with a longitudinal electron polarization between 80-87% were used to produce the circularly polarized photon beam. An additional carbon target, positioned downstream of the butanol target, was used to subtract the background from bound-nucleon reactions. The helicity asymmetry E was measured using the missing mass technique and compared to the SAID, BnGa and MAID PWAs with Juelich model.
• | Presentation)

• (Abstract |
  • We study the reaction e⁺ e → γ_ISR J/Ψ, where J/Ψ → π⁺ π^- π⁰ and J/Ψ → K⁺ K^- π⁰, using events obtained from the Initial State Radiation process. We measure the relative J/Ψ branching fraction and perform a Dalitz plot analysis of both J/Ψ decay modes using an isobar and a Veneziano model. We present also an analysis of the process  γγ → KK π. We observe the decays η_c → K_S K^+-π^-+ and η_c → K⁺ K^- π⁰ and perform a Dalitz analysis of both η_c decay modes. We also extract the mass dependent Kπ S-wave amplitude and phase using a model-independent partial wave analysis approach. These studies have been performed using the entire BaBar dataset collected at the PEP-II e⁺e^- collider.
• | Presentation)

• (Abstract |
  • Charmonium states below the open-charm threshold provide rich laboratory for studying the spectrum and interactions of mesons consisting of light quarks, in a low-background environment. Of special interest are _ΧcJ decays to three pseudo-scalar mesons, suitable for investigating two-body processes in which the production of exotic states with J^PC=1⁻⁺ decaying to the ηπ final state, like the _&pi1(1400) or _π1(1600), might be expected. We perform an amplitude analysis of the _Χ(2S) → γχ^c1; χ^c1 → ηπ⁺π⁻ decays, using 0.45 billion ψ(2S) produced at BESIII. A new decay mode of the _Χc1 is observed,  _Χc1 → a₂(1700)π, and we report a first non-zero measurement of the a0(980) coupling to the h¢p final state, using a0(980) → hp line shape. We do not observe the production of exotic mesons in the invariant mass range from 1.4 to 2.0 GeV/^c2.
• | Presentation)

• (Abstract |
  • We report the first observation of the very rare decay K^+- → π^+- π⁰ e⁺e^- by the NA48/2 experiment. From a clean sample of almost 2000 reconstructed signal events, we have determined the branching fraction with high precision and measured the e⁺e^- invariant mass distribution, which allows us to differentiate between different decay models. Also a detailed study of the K_e4 decay mode K → π⁰ π⁰ ev based on 65000 candidates with a low 1% background contamination is presented. The achieved experimental precision brings evidence for isospin breaking mass effects and final state ππ scattering. Theoretical calculations will have to face a new precision challenge when using such improved inputs to extract for example low energy constants of Chiral Perturbation Theory.
• | Presentation)

• (Abstract |
  • In this work we study the strong decays of charmed (strange) mesons up to orbitally-excited 1D and radially excited 2S states within the framework of the covariant oscillator quark model. In some transitions of highly excited charmed strange mesons, the final states can have large kinetic energy at the rest frame of initial states, although such an effect is neglected in the conventional treatment of nonrelativistic quark model. By contrast, the covariant oscillator quark model is a one of the possible relativistic extension to hold the various successes for the static problem in nonrelativistic quark model and it has remarkable features that hadrons are treated in a manifestly covariant way. In this work we have paid particular attention and carefully examined to this relativistic effect, and will discuss their impact. In practice, to evaluate the above transitions, we use the effective coupling vertex in the elementary emission model with suitable modification in conformity with our scheme. Based on the result of calculated widths, we discuss a possible assignment for newly-observed charmed (strange) mesons by BABAR, Belle and LHCb collaborations.
• | Presentation)

• (Abstract |
  • The COMPASS experiment at the CERN Super Proton Synchrotron has collected unprecedented data samples of diffractive reactions of 190 GeV pions with protons and heavier nuclear targets. The analysis efforts currently focus on final states including 3 pions or 2 pseudoscalars like ηπ,  η'π. A new narrow structure with axial-vector quantum numbers coupling exclusively to f₀(980) π has been observed at a mass of around 1.4 GeV. Interpretations of this intriguing and unexpected peak range from a 4-quark state to interferences of the α₁(1260) state with non-resonant processes. A possible explanation in terms of a dynamic singularity will be discussed. The status of the search for spin-exotic resonances will be presented, including new analysis methods and attempts to better model non-resonant background contributions.
• | Presentation)

• (Abstract |
  • The Laura++ package was originally developed for performing Dalitz plot analyses of B decays within the BaBar collaboration. Now publicly available (since September 2013) on the HepForge website it is used by numerous experimental collaborations worldwide. It has recently had two major features added: the ability to perform simultaneous fits and to float resonance parameters such as the mass and width. Additional features and extensions are in the pipeline. We report on the status and development plans (including a short tutorial) for this tool for performing amplitude analyses of three-body decays of hadrons.
• | Presentation)

• (Abstract |
  • First results from the Frozen Spin Target (FroST) at Jefferson Lab pave the way towards the understanding of the spectrum of excited baryons. Double polarization observables at an unprecedented precision put tight constraints on the amplitude as will be discussed. Conclusive answers in baryon spectroscopy are a long-sought goal. Necessary steps towards this goal will be discussed, such as statistical criteria, the need for hadron beams, and the need for a suitable amplitude parameterization to make future connections to ab-initio QCD approaches.
• | Presentation)

• (Abstract |
  • Resonances are extracted from different energy-dependent and single-energy fits to scattering data. The influence of recent precise EPECUR data is investigated. Results for the single-energy fits are derived using the L+P method of analysis and are compared to those obtained using contour integration applied to global energy dependent fits.
• | Presentation)

Parallel Sessions - 10:45 - 12:30

• (Abstract |
  • In recent years, the BESIII experiment has accumulated large samples of J/ψ, ψ' and ψ(3770) decays. Through radiative and hadronic charmonium decays, the baryon spectrum can be explored in a way that complements other existing data sets. In this talk, recent results in baryon spectroscopy at BESIII will be presented.
• | Presentation)

• (Abstract |
  • A primary approach in hadronic physics to understand quark-gluon interactions in baryons is to interpret the baryon spectrum in terms of the effective degrees of freedom. Lately, a significant amount of information about light baryon spectrum comes from the photo-production experiments. The current database of polarization observables in photo-production, however, is inadequate to understand the spectrum, particularly above 1.7 GeV c.m. energies. At these energies, the photo-absorption cross section is dominated by the production of multi-pion states and vector mesons. Therefore, it is essential to study vector meson decay modes of excited baryons in order to establish a resonance. The FROST (FROzen Spin Target)
    Experiment at Jefferson Lab using the CLAS detector has been performed with all possible combinations of beam-target polarizations and covers the c.m. energy regime up to 2.2 GeV. It provides a good platform to study the decay of excited baryon states to a large variety of final states, in particular to vector mesons such as ω and ρ. Here we report on polarization observables from FROST in  → ρω → ρπ⁺ π^-π⁰ using a transversely polarized butanol target and observables I^s,c, P_x,y and P_(x,y)^sc in γ^→ρ^→ → pπ⁺π^- using linearly polarized tagged photons and the transversely polarized target. The π⁺π^- photo-production reaction will allow for the study of ^N*→ pp decay modes. Many observables presented here are first-time measurements and will significantly augment the world database in an effort to approach a complete experiment in these final states that is necessary to determine contributing N^* resonances with minimal ambiguities. This work is supported by DOE #DE-FG02-92ER40735.
• | Presentation)

• (Abstract |
  • Compton scattering from protons and neutrons probes the two-photon response of the nucleon in electric and magnetic fields at fixed photon frequency and multipolarity. As these fields induce radiation multipoles by displacing the target constituents, the angular and energy dependence of the emitted radiation provides detailed tests of the symmetries and strengths which govern the interactions of the constituents with each other and with photons. At low energies, the process is parameterized by six energy-dependent dipole polarizabilities. Their zero-energy limits are the static electric and magnetic scalar dipole polarizabilities aE1 and bM1, and the four spin-polarizabilities. Differences between proton and neutron values stem from isospin-breaking interactions, exploring the interplay between chiral symmetry as well as the pattern of its breaking, and short-distance Physics. The information is for convenience often compressed in the static scalar dipole polarizabilities, i.e. the extrapolated values at zero photon energy. In combination with emerging lattice QCD determinations, they provide stringent tests for our theoretical description of hadron structure and are thus fundamental quantities in their own right. Moreover, they are crucial to the neutron-proton mass difference, the proton charge radius puzzle, and the Lamb shift of muonic hydrogen.
    Recently, new extractions of the static electric and magnetic scalar dipole polarizabilities of the proton and neutron from all published elastic data below 300 MeV were performed in Chiral Effective Field Theory. ChiEFT is ideal for that purpose since it provides reliable theoretical uncertainties by a model-independent estimate of higher-order corrections and encodes the correct low-energy dynamics of QCD, including, for few-nucleon systems, consistent nuclear currents, rescattering effects and wave functions. The proton and neutron values turn out to be identical within the accuracy of available data.
    After reviewing context, ingredients and results of the analyses, this talk discusses the following topics: statistical consistency of the world Compton dataset; status of one- and few nucleon Compton theory; desirable improvements of the database; elastic and inelastic Compton scattering on deuterons and 3He; and predictions for high-intensity experiments with polarized targets an polarized beams; and comparison to emerging lattice QCD determinations. The goal is to extract not only scalar nucleon polarizabilities, but also the to-date poorly-explored spin-polarizabilities which parametrize the stiffness of the nucleon spin in external electro-magnetic fields (nucleonic bi-refringence/Faraday effect).
• | Presentation)

• (Abstract |
  • One of the remaining challenges within the standard model is to gain a good understanding of QCD in the non-perturbative regime. One key step toward this aim is baryon spectroscopy, investigating the spectrum and the properties of baryon resonances. To gain access to resonances with small πN partial width, photo-production experiments provide essential information. In order to extract the contributing resonances, partial wave analyses need to be performed. Here, a complete experiment is required to unambiguously determine the contributing amplitudes. This involves the measurement of carefully chosen single and double polarization observables. The CBELSA/TAPS experiment with a longitudinally or transversely polarized target and an energy tagged, linearly or circularly polarized photon beam allows the measurement of a large set of polarization observables. Due to its good energy resolution, high detection efficiency for photons, and the nearly complete solid angle coverage it is ideally suited for the measurement of photo-production of neutral mesons decaying into photons. In this talk recent results for various double polarization observables in single- and multi-meson final states will be presented and their impact on the partial wave analysis will be discussed. Supported by DFG within CRC 16.
• | Presentation)

• (Abstract |
  • Recent experiments using the Crystal Ball/TAPS setup at the MAMI accelerator in Mainz, Germany continue to study the properties and the excitation spectrum of the nucleon with meson photo production. Electromagnetic excitations of the proton and neutron are essential for understanding their isospin decomposition. The electromagnetic coupling of photons to protons is different than that of neutrons in certain states. Hence, a complete partial wave analysis (PWA) can assist in yielding more information about any reaction, but requires the determination of polarization observables. Polarization observables play a crucial role as they are essential in disentangling the contributing resonant and non-resonant amplitudes, whereas cross-section data alone is not sufficient for separating resonances. Preliminary results of polarization observables of η and π production off a polarized proton (H-butanol) and polarized neutron (D-butanol) target will be shown with comparison to predictions of recent multipole analyses. These results will allow for developing the world database.
• | Presentation)

• (Abstract |
  • The past decade witnessed a remarkable proliferation of exotic charmonium-like resonances discovered at accelerators. In particular, the recently observed charged states are clearly not interpretable as qqbar mesons. Notwithstanding the considerable advances on the experimental side, conflicting theoretical descriptions do not seem to provide a definitive picture about the nature of the so-called XYZ particles. We show that the most recent experimental discoveries at BESIII fit a comprehensive description in terms of compact four-quark particles (tetraquarks). Moreover, we discuss some unexplored decay channels which are particularly sensitive to the different phenomenological models, and could shed some light on the nature of XYZ states.
• | Presentation)

• (Abstract |
  • The BESIII Experiment at the Beijing Electron Positron Collider (BEPC2) collected large data samples for electron-positron collisions with center-of-mass above 4 GeV during 2013 and 2014. A number of hadronic transitions have been measured in these data samples, leading to a rather complex picture of the physics of charmonium above 4 GeV. In this talk we will present results for e⁺e^- to π⁰π⁰ J/ψ (where the Y(4260) is seen in the cross section), as well as results for apparently more complex cross sections, such as e⁺e^- to ω _ΧcJ and η J/Ψ, where structures are less apparent.
• | Presentation)

• (Abstract |
  • The BESIII Experiment at the Beijing Electron Positron Collider (BEPC2) collected large data samples for electron-positron collisions with center-of-mass above 4 GeV during 2013 and 2014. In this mass region, there are several states that are yet to be understood. In this talk we will discuss BESIII analyses of radiative transitions among these states, which may improve our understanding of this important mass region. One example is the observation of the process e⁺e^- → γX(3872).
• | Presentation)

• (Abstract |
  • The high prompt production cross section of X(3872) at hadron colliders has shown to be very informative about the quark nature of the XYZ states. We present some results on X production in pp(ρbar) collisions obtained with Monte Carlo hadronization methods, and illustrate what can be learned from their use to improve our understanding of exotic states. In particular, a comparison between anti-deuteron and X production cross sections is proposed. Hadronization might be the key to solve the problem of the extra states expected in diquark-antidiquark models which are naturally favored after the recent confirmation of the Z(4430) tetraquark, together with its lower partners Z_c(3900) and Z_c2(4020).
• | Presentation)

• (Abstract |
  • In the present paper we address the interaction of pairs of charmed mesons with hidden charm in a finite box. We use the interaction from a recent model based on heavy-quark spin symmetry that predicts molecules of hidden charm in the infinite volume. The energy levels in the box are generated within this model, and from them some synthetic data are generated. These data are then employed to study the inverse problem of getting the energies of the bound states and phase shifts for D{Dbar} or D^*{Dbar}^*. Different strategies are investigated using the lowest two levels for different values of the box size, and the errors produced are studied. Starting from the upper level, fits to the synthetic data are carried out to determine the scattering length and effective range plus the binding energy of the ground state. A similar strategy using the effective range formula is considered with a simultaneous fit to the two levels one above and the other one below the threshold. This method turns out to be more efficient than the previous one. Finally, a method based on the fit to the data by means of a potential and a conveniently regularized loop function, turns out to be very efficient and allows us to produce accurate results in the infinite volume starting from levels of the box with errors far larger than the uncertainties obtained in the final results. A regularization method based on Gaussian wave functions turns out to be rather efficient in the analysis and as a byproduct a practical and fast method to calculate the Lüscher function with high precision is presented.
• | Presentation)

• (Abstract |
  • In the BESIII experiment, we explore Double Collins Asymmetries by looking at the two back-to-back charged pions. BEIII experiment is an electron-position collider running at 2<Q<4.6 GeV energy region, which has similar energy coverage with the SIDIS experiments. This analysis is carried out based on ~65 pb^-1 data at Q=3.65 GeV and will provide the first measurement of Collins asymmetry at low Q. This analysis results will be reported.
• | Presentation)

• (Abstract |
  • Inclusive hadron production cross sections and angular distributions in e⁺e- collisions shed light on fundamental questions of hadronization and fragmentation processes. We present measurements of the so-called Collins azimuthal asymmetries in inclusive production of hadron pairs, in the e⁺e^- → h₁ h₂ X annihilation process, where the two hadrons (either kaon or pions) are produced in opposite hemispheres. The data collected by the BaBar detector allows the determination of the Collins fragmentation function as a function of hadron fractional energies and transverse momenta, and can be combined with semi-inclusive deep-inelastic-scattering data to extract the transversity distribution function, which is the least known leading-twist component of the QCD description of the Partonic structure of the nucleon.
• | Presentation)

• (Abstract |
  • We have studied the chiral odd Generalized Parton Distributions (GPDs) in the impact parameter space by assuming a flexible parametrization in a quark-diquark model. The explicit contributions from the up and down quarks have been obtained by considering both the scalar (spin-0) and the axial-vector (spin-1) configurations for the diquark. The spin densities for the up and down quarks in this model have also been studied for the monopole, dipole and quadrupole contributions for unpolarized and polarized quarks in unpolarized and polarized proton.
• | Presentation)

• (Abstract |
  • At the COMPASS experiment at CERN, pion-photon reactions are investigated using the Primakoff effect, where high-energetic pions react with the quasi-real photons surrounding the target nuclei. The production of a single hard photon in such a pion scattering, at lowest momentum transfer to the nucleus, is related to pion Compton scattering. Studying the energy distribution of the outgoing photons, the pion polarizability can be extracted. In addition to the measurement with a pion beam, control measurements with a muon beam allow to estimate the systematics. The COMPASS result is in tension with earlier dedicated measurements and rather in agreement with the theoretical expectation from chiral perturbation theory. Based on the same dataset, reactions with neutral and charged pions in the final state are studied. At low invariant mass of the pion-photon system, these reactions are governed by chiral dynamics. Using partial-wave analysis techniques, the absolute cross sections for the production of π^-π⁺π^- and π^-π⁰π⁰ final states from π^-γ  interactions are measured and compared to predictions from chiral perturbation theory. At higher pion-photon masses, the production of 3π resonances is studied with the focus on their radiative couplings.
• | Presentation)

• (Abstract |
  • 
• | Presentation)

Plenary Sessions - 2:00 - 6:00                                                        Grand Ballroom II

• (Abstract |
  • The LHC opens the door to searches for excited heavy-flavored baryons and mesons. New results on orbitally excited B mesons, b-baryons and D mesons are presented. For the latter, decays of B mesons provide a well-defined and clean initial sample allowing the unambiguous determination of quantum numbers.
• | Presentation)

• (Abstract |
  • I report the recent analyses on conventional and exotic states from Belle experiment.
• | Presentation)

• (Abstract |
  • A great deal of information on the spectrum of baryons can be obtained from meson photo production and electro production experiments. This talk will present an overview of the many results published from measurements at Jefferson Laboratory, including both cross-sections and polarization observables. These results will be compared with existing and complementary data sets from other labs, and their influence on theoretical models will be examined. What we have learned so far, and the prospects for obtaining amplitude level information through complete experiments will also be discussed.
• | Presentation)

• (Abstract |
  • In this talk I discuss some issues relevant for the amplitude analysis of hadronic reactions and the extraction of resonance properties. Those issues include the role of unitarity, dispersion theory, cusps as well as the effect of multi-particle intermediate states.
• | Presentation)

• (Abstract |
  •  
• | Presentation)

• (Abstract |
  • In this talk, we will present a brief overview of recent results on measured decay properties and production cross sections of B hadrons performed by the ATLAS experiment with the full LHC Run 1 statistics. We will concentrate mainly on the recent measurements of properties of the B_c, B_s and B_d mesons and the Λ_b baryon. For the B_c meson, the results of the measurement of the relative cross-section, relative branching fractions and observation of the excited state B_c(2S) will be presented. These measurements provide a valuable test of theoretical calculations involving two heavy quarks. Furthermore, we will show recent results of measurements of decay amplitudes of B_s and B_d meson decays which are sensitive to a potential physics beyond the Standard Model. The measurement of the relative branching fraction of the decay Λ_b → ψ(2S)+Λ will also be presented and compared to the known decay of B_d → ψ(2S)+K_S. In addition to studies of the B hadrons, the talk will include measurement of the differential cross-section of the X(3872) state through its decays to J/ψ π π final state and a search for its bottomonium counterpart X_b.
• | Presentation)

Friday, September 18, 2015

Parallel Sessions - 8:30 - 10:15

• (Abstract |
  • Studying excited nucleon structure through exclusive electroproduction reactions will be an important avenue for exploring the nature of the nonperturbative strong interaction. Electro-couplings for N* states in the mass range below 1.75 GeV have been determined from analyses of CLAS πN, ηN, and ππN data. This work made clear that consistency of independent analyses of exclusive channels with different couplings and non-resonant contributions but the same N* electro-excitation amplitudes, is essential to have confidence in the extracted results. In terms of hadronic coupling, many high-lying N* states preferentially decay through the ππN channel instead of πN. Data from the KY channels will therefore be critical to provide an independent analysis to compare the extracted electro-couplings for the high-lying N* states against those determined from the ππN channel. A program to study excited N* decays to non-strange and strange exclusive final states using CLAS12 at JLab will be discussed that will measure differential cross sections to be used as input to extract the γvNN* transition form factors for the most prominent N* states in the range of invariant energy W up 3 GeV in the virtually unexplored domain of momentum transfers Q² up to 12 GeV2.
• | Presentation)

• (Abstract |
  • Compton scattering processes are ideal to study electric and magnetic dipole polarizability coefficients of nucleons. These fundamental quantities parametrize the response to a monochromatic photon probe. In this work, the inelastic channel γd → γnp is treated in _χEFT, with a focus on the NQFP - neutron quasi-free peak – kinematic region. In this region, the momentum of the outgoing proton is small enough that it is considered to remain at rest. This provides access to the Compton scattering process γn → γn from which the neutron scalar polarizabilites α and β are extracted. Using _χEFT, differential cross-sections, d³σ/dE_ndΩγΩ_n, in the photon energy range of 200-400 MeV are computed. The biggest contribution comes from the impulse approximation, with small corrections stemming from final state interaction, meson exchange currents and rescattering. A new extraction of neutron polarizabilities from a two-parameter fit to the Kossert et al. data taken at MAMI in 2002 is presented. Previously, the experiment was designed and the data analyzed based on a theoretical model that computed the NQFP differential cross-sections. The re-analysis of this data in a consistent, model independent framework - _χEFT - provides reliable extraction of polarizabilities with controlled uncertainties.
• | Presentation)

• (Abstract |
  • Cross sections for the reactions γπ → pπ⁺π^– and γp → pω have been measured, covering the photon energy range from 1.15 GeV to 5 GeV. The g12 experiment was performed at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS) using an unpolarized hydrogen target and circularly-polarized photons produced from bremstrahlung of longitudinally-polarized electron with energy 5.7 GeV. The cross section allows the study of excited baryon decays to pρ and pω. However, performing partial wave analysis using differential cross sections alone to extract resonance is difficult because of the overlapping nature among resonances. Polarization observables are sensitive to the interference of resonances in the scattering amplitude. Hence the beam helicity asymmetry measurement for γp → pπ⁺π^– is also presented. The results are compared with previous measurements from CLAS and also some model calculations. Our data are in good agreement with previous CLAS measurements but show discrepancies with model predictions.
• | Presentation)

• (Abstract |
  • The first-time measurement of the angular dependence of the beam-helicity asymmetry is shown γp → pK⁺K^- and is compared γp → pπ⁺π^-. The data obtained were from the CLAS g12 experiment at Jefferson Lab. The experiment utilized a beam of circularly-polarized photons with energies between 1.1 to 5.4 GeV incident on an unpolarized liquid hydrogen target. An unprecedented number of hadrons with strange quarks in photo-production were observed in g12. The production mechanism for hadrons containing strange quarks is not well understood. The beam-helicity asymmetry is a polarization observable that provides information on competing production mechanisms in the reaction. It is shown that the asymmetry is sensitive to several kinematic variables (Mandelstam t, √s, M(K⁺K^-), M(pK^-)) that are key observables in modeling the reaction's dynamics. Furthermore, the comparison of the beam-helicity asymmetries between the kaon and pion channels serve as a platform for the investigation of its flavor dependence. Its significance to understanding the production mechanisms of intermediate resonances is also discussed.
• | Presentation)

• (Abstract |
  • The Λ(1405) baryon is of continued interest in hadronic physics, being absent in many quark model calculations and supposedly manifesting itself in a two-pole structure. Finite-volume Lattice-QCD eigenvalues for different quark masses were recently reported by the Adelaide group. We compare these eigenvalues to those of a unitary Chiral Perturbation Theory (UCHPT) model evaluated in the finite volume. The UCHPT calculation predicts the quark mass dependence remarkably well. It also explains the overlap pattern with different meson-baryon components, mainly π∑ and KbarN, at different quark masses. More accurate Lattice QCD are required to draw definite conclusions on the nature of the Λ(1405).
• | Presentation)

• (Abstract |
  • Charmless B meson decays to pseudoscalar or vector mesons are sensitive to physics beyond the Standard  Model through the appearance of unexpected angular distributions or CP violating phases. Measurements of polarization fractions and  T-odd asymmetries are presented for several decay channels of high interest. Large local CP asymmetries have been seen in the Dalitz plane, indicating long-distance "rescattering" effects.
• | Presentation)

• (Abstract |
  • BESIII collected 506 pb^-1 sample at c.m. energy of 4.6 GeV, which allows us to perform the double-tag technique to measure the rates in the model-independent way near threshold for the first time. Herein, we present our analysis results on branching fractions for 12Λ⁺_c hadronic decays, including Λ⁺_c to pK^-π⁺. In addition, we will present the results of the semi-leptonic decay Λ_c⁺to Λe⁺ν.
• | Presentation)

• (Abstract |
  • Using the 980 fb⁻¹ full data sample taken with the Belle detector, there are measurements finished recently. The measurement on e⁺e⁻ → π⁺π⁻ψ(2S) between 4.0 and 5.5 GeV via initial state radiation will be reviewed. Y(4260) may exist in the π⁺π⁻ψ(2S) final states, but not significantly. Intermediate state is searched for in both Y(4360) and Y(4660) decays, and an excess on 4.05 GeV/c² is found in Y(4360) decays. However, the significance is only 3.5σ. Like in the measurement of e⁺e⁻ → π⁺π⁻ψ(2S), many studies on exotic hadrons at Belle show interesting results but are limited by statistics. The future B-factory will take much huge data samples. The data samples will improve current Belle measurements and allow many new studies on the exotic hadrons. The future B-factory is expected to answer a lot of questions about the nature of exotic hadrons.
• | Presentation)

• (Abstract |
  • In this talk we report on the work of Ref. [1]. We study the Bbar_s⁰ → D_sbar (KD)⁺ weak decay, and look at the KD invariant mass distribution, for which we use recent lattice QCD results for the KD interaction from where the D_s^*₀(2317) resonance appears as a KD bound state. Since there are not yet experimental data on this reaction, in a second step we propose an analysis method to obtain information on the D_s^*₀(2317) resonance from the future experimental KD mass distribution in this decay. For this purpose, we generate synthetic data taking a few points from our theoretical distribution to which we add a 5% or 10% error. With this analysis method, we prove that one can obtain from these “data” the existence of a bound KD state, the KD scattering length and effective range and most importantly, the KD probability in the wave function of the bound state obtained, which was found to be largely dominant in lattice QCD studies. This means that one can obtain information on the nature of the D_s^*₀(2317) resonance from the implementation of this experiment, in the line of finding the structure of resonances, which is one of the main aims in hadron spectroscopy.
    

    Reference:
    [1]  M. Albaladejo, M. Nielsen and E. Oset, Phys. Lett. B 746, 305 (2015)

                [arXiv:1501.03455 [hep-ph]]
• | Presentation)

• (Abstract |
  • We study the semi-leptonic B_s and B decays into the D*_s0(2317) and D*₀(2400) resonances, respectively. With the help of a chiral unitarity model in coupled channels we compute the ratio of the decay widths of both processes. Using current values of the width for the Bbar⁰ to D*₀(2400)^{+},ν₁, 1^- we make predictions for the rate of the Bbar_s⁰ to D*_s0(2317)⁺, ν₁^{-} decay and for the DK invariant mass distribution in the Bbar_s⁰ to D, K, νbar₁, 1^- decay. These predictions are tied to the nature of the D*_s0(2317) and D*₀(2400) resonances as molecular states of mostly KD and KD^*, respectively, and we discuss that its measurement can shed light on the nature of these resonances.
• | Presentation)

• (Abstract |
  • Photo-production of the π⁰ meson was studied using the CLAS detector at Thomas Jefferson National Accelerator Facility using tagged incident beam energies spanning the range E_γ = 1.1 GeV - 5.45 GeV. The measurement is performed on a liquid hydrogen target in the reaction γp → pe⁺e^-(γ). The final state of the reaction is the sum of two sub processes for π⁰ decay, the Dalitz decay mode of π⁰ → e⁺e^-γ and conversion mode where one photon from π⁰ → γγ decay is converted into a e⁺e^- pair. This specific final state reaction avoided limitations caused by single prompt track triggering and allowed a kinematic range extension to the world data on π⁰ photo production to a domain never systematically measured before. We report the measurement of the π⁰ differential cross-sections dσ/dΩ and dσ/dt . The angular distributions agree well with the SAID parametrization for incident beam energies below 3 GeV, while an interpretation of the data for incident beam energies greater than 3 GeV is currently being developed. Included in the report will be a discussion of the future wide angle, exclusive photo production of p0experiment that will be performed in Hall C.
• | Presentation)

• (Abstract |
  • I will present a detailed measurement of positive pion photoproduction in the 730-2300 MeV photon energy (1400-2280 MeV centre-of-mass energy) region with a linearly polarized photon beam and a longitudinally polarized proton target with a close-to-complete angular coverage in detection of the reaction products. This unique set up allows for the extraction of the double-polarization observable, G. The data were taken as part of the g9 experiment at the Thomas Jefferson National Accelerator Facility in Virginia, using a tagged, polarized photon beam and the Frozen Proton Spin Target, FROST, in conjunction with the CEBAF Large Acceptance Spectrometer, CLAS. The results of the study presented here are compared to the existing data set for the G double-polarization observable along with the current solutions of the three main partial wave analyses: MAID, SAID and Bonn-Gatchina.
• | Presentation)

• (Abstract |
  • A kaonic atom, which is a Coulomb-bound system of a negatively charged kaon and a nucleus, is a unique tool to study the strong interaction between anti-kaon and nucleus in the low-energy limit. The strong-interaction shifts and widths of various kaonic atoms have been measured so far, and the optical potential of the K^- -nucleus system is studied systematically. However, the depth of the optical potential is still not determined due to the lack of precision in experimental results. Presently, both the “deep-potential” phenomenological approach [1, 2] and the “shallow-potential” chiral-unitary model [3] can explain the measured strong-interaction shifts and widths. To solve the “deep or shallow” problem it is important to understand the bound states of anti-kaon in the nucleus; thus a new precise measurement has been awaited to break this degeneracy.
    Our goal is to perform high-resolution x-ray spectroscopy of kaonic atoms with an array of superconducting transition-edge-sensor (TES) micro calorimeters [4] at J-PARC. The TESs have achieved eV-scale energy resolution in spectroscopy of hard X-rays. Because of its combination of energy resolution and collecting efficiency, an array of TESs is a powerful tool to determine the strong-interaction shift and width. We will measure the kaonic ³He and ⁴He 3d → 2p x-rays with precision of ±0.2 eV for the strong-interaction shift in the J-PARC E17 experiment [5]. This outstanding precision could distinguish the small difference between the phenomenological approach and the chiral unitary model. In this contribution, we will present a unique possibility to solve the “deep or shallow” problem in K^- -nucleus optical potential, and also discuss the feasibility of the J-PARC E17 experiment on the basis of the pionic atom spectroscopy with an array of TESs at PSI. We have determined the central energy of the pionic carbon 4→3 line with precision of ±0.1 eV. This result proves the viability of our new measurement technique based on the TESs.
    

    References:
    [1]  C.J. Batty, E. Friedman, A. Gal, Phys. Rep. 287, (1997) 385
    [2]  E. Friedman, Int. J. Mod. Phys. A 26, (2011) 468
    [3]  S. Hirenzaki et al., Phys. Rev. C 61, (2000) 055205
    [4]  K.D. Irwin and G.C. Hilton, "Transition-Edge Sensors", C. Enss Ed., Cryogenic
    Particle Detection, Springer-Verlag, vol.99, 63-149 (2005)
    [5]  R.S. Hayano et al., J-PARC E17 proposal, https://j-parc.jp/researcher/

    Hadron/en/pac_0606/pdf/p17-Hayano.pdf
• | Presentation)

• (Abstract |
  • The interaction of antikaons (K^-) with nucleons and nuclei in the low-energy regime represents a research field with high impact on theory in hadron physics. There are important open questions like the question of antikaon nuclear bound states like the prototype system being K-pp. A unique and rather direct experimental access to the antikaon-nucleon scattering lengths is provided by precision X-ray spectroscopy of transitions in low-lying states in light kaonic atoms like kaonic hydrogen and helium isotopes. In the SIDDHARTA experiment at the electron-positron collider DAFNE of LNF-INFN we measured the most precise values of the strong interaction observables, i.e. the strong interaction on the 1s ground state of the electromagnetically bound K-p atom leading to energy shift and broadening of the 1s state. The SIDDHARTA result triggered new theoretical work, which achieved major progress in the understanding of the low-energy strong interaction with strangeness reflected by the Antikaon-nucleon scattering lengths calculated with the K-p amplitudes constrained by the SIDDHARTA data. The talk will give an overview of the experimental results of SIDDHARTA, the implications for the theory of low-energy strong interaction with strangeness and will provide an outlook to future developments in this research field.
• | Presentation)

• (Abstract |
  • The AMADEUS experiment deals with the investigation of the low-energy kaon-nuclei hadronic interaction at the DAFNE collider at LNF-INFN, which is fundamental to respond longstanding questions in the non-perturbative strangeness QCD sector. One of the most interesting aspects is to understand how hadron masses and interactions change in the nuclear environment. The antikaon-nucleon potential is investigated searching for signals from possible bound kaonic clusters, which would open the possibility for the formation of very dense baryonic matter and imply a deep attractive antikaon-nucleon potential. The confirmation of this scenario may imply a new fundamental role of strangeness in astrophysics. AMADEUS step 0 consisted in the reanalysis of 2004/2005 KLOE data, exploiting K^- absorptions in H, ⁴He, ⁹Be and ¹²C, leading to the first invariant mass spectroscopy study with in-flight negative kaons. The study of Λ-p, Λ-d and Λ-t correlations will be presented with the investigations of single and multi-nucleon absorption and internal conversion processes. The results obtained in the analysis of the ∑⁺π^- and ∑⁰π⁰ (pure isospin 0) channels, intended to shed light on the controversial nature of the Λ(1405) state will be presented as well, together with the analysis of the Λ(∑⁰)π^- channel, from which the measurement of the module of the isospin 1, S-wave non-resonant transition amplitude can be extracted for the first time.
• | Presentation)

Parallel Sessions - 10:45 - 12:30

• (Abstract |
  • Photo-production experiments with the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Laboratory produce data sets with unprecedented statistics of light mesons. With these data sets, measurements of transition form factors for η, ω, and η′ via conversion decays can be performed using a line shape analysis on the invariant mass of the final state dileptons. Tests of fundamental symmetries and information on the light quark mass difference can be performed using a Dalitz plot analysis of the meson decay. In addition, the data allows for a search for dark matter, such as the heavy photon via conversion decays of light mesons and physics beyond the Standard Model can be searched for via invisible decays of I·mesons. An overview of the first results and future prospects within the newly upgraded CLAS apparatus will be given.
• | Presentation)

• (Abstract |
  • In this talk we present preliminary experimental results of Dalitz plot analysis of the decay η' → ππη, based on the CLAS data collected during photo-production experiment γp → pη' for the center-of-mass energy from 1.96 to 2.72 GeV at Jefferson Lab. The analysis is based on the highest statistics collected in this channel in comparison to the other experiments reported so far. The high statistics will enable us to report precise Dalitz plot parameters with low statistical errors.
• | Presentation)

• (Abstract |
  • The γp → ΛK⁺π⁺π^- reaction provides an opportunity to study the photo-production of excited strange mesons in the K⁺π⁺π^- system using the g12 experiment dataset at Jefferson Lab. The g12 experiment used the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab with a liquid hydrogen target and a 4-5.5 GeV tagged photon beam, producing over 26 billion events of different topologies. The Λ in this reaction is identified via the pπ^- decay mode. Studies indicate two dominating decay modes in the K⁺π⁺π^- system: the K^*π⁺ mode and the K⁺ρ mode. Studies of the angular distributions and dynamical features are being performed. Preliminary results of features of the data will be presented.
• | Presentation)

• (Abstract |
  • Apart from the mesons that the constituent quark model predicts, QCD allows for additional states beyond the qqbar system. Previous experiments have performed partial wave analysis on pion-production data and claim observation of a J^PC = 1⁻⁺ state decaying via ρπ. The g12 experiment took place at Jefferson Lab using the CLAS spectrometer, a liquid hydrogen target was used and a tagged photon beam. By studying the reactions γp →nπ⁺π⁺π^- and γp→Δ⁺⁺π⁺π^-π^-, we are analyzing a large data-set of a three pion system. In the first reaction channel, events are selected with low four-momentum transfer to the neutron, in order to enhance one pion exchange production. The latter reaction is expected to be dominated by pion exchange between the baryon and the 3p meson system, given identification of Δ++ in the event. For both 3π systems the data exhibit two intermediate decays, ρπ and f2π. An analysis of the kinematics and dynamics of those two data-sets is in progress, as well as a study of the angular distributions looking for resonance contributions. Preliminary results will be shown.
• | Presentation)

• (Abstract |
  • There is little known about the baryon-antibaryon photo-production mechanism. Three reactions, γp → pppbar, γp → ppnbarπ^-, and γp → pnpbarπ⁺  have been investigated for the photon energy range of 4.4-5.45 GeV. The data were from the g12 experiment taken with the CLAS detector using a liquid hydrogen target in Hall B at Thomas Jefferson National Accelerator Facility. This experiment had high statistics, with an integrated luminosity of 68 pb^-1. General features of the data, preliminary cross sections and preliminary partial wave analysis results for the ppbar system will be discussed.
• | Presentation)

• (Abstract |
  • The structure of heavy mesons located above the thresholds for the open flavor production has been largely discussed in the recent years. Their conventional description as pure B{Bbar}  bound state has been called into question by the study of the hadronic transitions to the lower states, and the observation of charged exotic states has highlighted the importance of the light quark degrees of freedom in the description of both charmonia and bottomonia. We will report the most recent experimental measurements performed by the Belle collaboration in the Y(4S), Y(5S) and Y(6S) regions, including the measurement of the ratio σ(e⁺e^- → bbbar)/σ(e⁺e^- to μ⁺μ^-), the search for neutral states near the B⁰ Bbar⁰ threshold, the first observation of the transition Y(4S) to η h_b(1P) and the study of the η transitions at the Y(5S) energy. The contribution to the study of the structure of these states coming from the measurement of hadronic transitions will be discussed.
• | Presentation)

• (Abstract |
  • A new non-relativistic quark model for the description of heavy quarkonia, called henceforth, Generalized Screened Potential Model, has been developed [1]. The model is based on the assumption that a heavy quark meson description can be obtained from the consideration of effective valence quark degrees of freedom interacting through a potential that incorporates screening effects from meson-meson configurations. This potential is generated by means of a Born-Oppenheimer approximation from the lattice results [2] for the energy of two static color sources (heavy quark and heavy antiquark), in terms of their distance, when the mixing of the quenched quark-antiquark configuration with open flavor meson-meson ones is taken into account. This results in an energy dependent potential in the sense that in each energy region delimited by neighbor meson-meson thresholds it has a Cornell form but modulated by the corresponding thresholds. When applied to bottomonium a good spectral description of well-established resonances is obtained and a richer high energy spectrum (bigger number of bound states) than the one resulting from the non-screened Cornell potential is predicted. However, the current lack of data does not allow validating or refuting this prediction. In this regard the application of the model to charmonium is more determinant since a plethora of additional states, not fitting into the conventional non-screened Cornell potential framework, has been discovered in the last ten years (see [3.5] and references therein). More precisely, the model allows for a quite reasonable assignment of calculated J⁺⁺ states to conventional and non-conventional resonances, all of them corresponding to bound states of the constructed potential. In particular a nice description of the masses and electromagnetic transition rates for X(3872) and X(3915) comes out. Furthermore, the model gives definite predictions about the existence of new states.
    

    References:
    [1]  P. González, J. Phys. G. 41, 095001 (2014); arXiv:1406.5025 [hep-ph]
    [2]  G. S. Bali et al. (SESAM Collaboration), Phys. Rev. D71, 114513 (2005)
    [3]  K. A. Olive et al. [Particle Data Group (PDG)], Chin.Phys. C 38, 090001 (2014)
    [4]  S. L. Olsen, Front.Phys. 10 (2015) 101401; arXiv:1411.7738 [hep-ex]

    [5]        N. Brambilla et al., Eur. Phys. J. C 71, 1534 (2011)
• | Presentation)

• (Abstract |
  • Charm and charmonium physics have gained renewed interest in the past decade. Recent spectroscopic observations strongly motivate these studies. Among the several possible reactions, measurements in proton-antiproton annihilation play an important role, complementary to the studies performed at B-factories. The PANDA experiment at FAIR (Darmstadt, Germany), conceived to study antiproton annihilations, will investigate fundamental questions of hadron and nuclear physics in the interactions of antiprotons with nucleons and nuclei. Among other topics, original contributions are expected from PANDA in the open-charm sector. With reaction rates as large as 2.10⁷ interactions/s, and a mass resolution 20 times better as compared with the most recent B-factories, PANDA is in a privileged position to successfully perform the measurement of the width of narrow states such as the D_s(2317), the D_s(2460), and the X(3872). These measurements are essential to understand their nature, and discriminate among various theoretical models which explain their origin. PANDA will investigate also high spin particles, whose observation was forbidden at B-factories. Original contributions are expected for the ppbar annihilation cross section measurements to open charm, for which several theoretical models exist leading to different expectations. The status of the current simulations of these channels in PANDA will be shown, with evidence on the original contribution that PANDA will be able to deliver in the study of the D_SJ^(*), of Y states above the DD^* threshold, and F-wave charmonium states.
• | Presentation)

• (Abstract |
  • We investigate the decay of Bbar⁰ to Kbar^{*0}R and Bbar_s⁰ to ΦR with R being the X(4160, Y(3940), Z(3930) resonances. Under the assumption that these states are dynamically generated from the vector-vector interaction, as has been concluded from several theoretical studies, we use a reaction mechanism of quark production at the elementary level, followed by hadronization of one final qqbar pair into two vectors and posterior final state interaction of this pair of vector mesons to produce the resonances. With this procedure we are able to predict five ratios for these decays, which are closely linked to the dynamical nature of these states, and also predict the order of magnitude of the branching ratios which we find of the order of 10^{-4}, well within the present measurable range. In order to further test the dynamical nature of these resonances we study the Bbar_s⁰ to ΦD^*Dbar^* and Bbar_s⁰ to ΦD_s^* Dbar_s^*  decays close to the D*Dbar^* and D_s^*  thresholds and make predictions for the ratio of the mass distributions in these decays and the Bbar_s⁰ to ΦR decay widths. The measurement of these decays rates can help unravel the nature of these resonances.
• | Presentation)

• (Abstract |
  • The MesonEx experiment with CLAS12 will join the global effort to perform a comprehensive study of the meson spectrum in the light quark sector. The new generation of experiments including GluEx and COMPASS are generating huge statistics. Likewise MesonEx, utilizing quasi-real photons will be required to handle millions of events in mass bins of the produced mesons. At this level systematic effects from experiment and theory must be treated very carefully. This talk will outline the framework being developed through the HASPECT collaboration combining ROOT based data handling with new theoretical approaches via Indiana AmpTools and modern statistical analysis techniques.
• | Presentation)

• (Abstract |
  • The Joint Physics Analysis Center (JPAC) between Indiana University and Jefferson Lab has been developing analysis tools for hadron spectroscopy during the last two years. This talk summarizes JPAC efforts on elastic scatterings (pion-nucleon and kaon-nucleon), decays (eta and omega decays in three pions) and single meson photo-production.
• | Presentation)

• (Abstract |
  • The PyPWA software framework is used to perform Partial Wave and Amplitude Analysis (PWA) with the goal of extracting resonance information from multi-particle final states. More generally, it can also be used to t a parametric model to the data by performing extended likelihood fits. PyPWA is directed to photo-production experiments using linear polarized beams. Although general amplitudes can be used, the framework includes a realization of the Isobar model, with extensions to include Deck-type and baryon vertices corrections. We describe the general structure of the framework. Most of the code is in Python, but hybrid code (in Cyhon or Fortran) has been used when appropriate. Scripting for use of the JLab Linux computer farm is included and for parallel coprocessors (Xeon-Phi or GPUs) will be also included in the near future. The goal of this software framework is to create a user friendly environment for PW/Amplitude analysis of linear polarized photo-production experiments.
• | Presentation)

• (Abstract |
  • There has been significant interest in the physics of heavy quarkonia for over ten years. This resurgence was stimulated by discoveries of narrow peaks in the spectrum. Such peaks may indicate existence of new exotic hadrons, commonly referred to as the XYZ states. Although the quark model provides a reasonably accurate description for heavy quarkonia, it does not predict the existence of these exotic states. There are many models trying to explain the XYZ's such as mesonic molecular or tetraquark states. We use amplitude analysis methods to study the reaction channels where the peaks appear, and show that some of these peaks may be enhanced due to anomalous kinematic singularities in the reaction amplitude. In particular, the X(3872) is studied in the DD* system.
• | Presentation)

Plenary Sessions - 2:00 - 4:15                                                        Grand Ballroom II

• (Abstract |
  • Chiral effective field theories represent a crucial tool for hadronic physics, in particular in combination with dispersion relations. We will review both techniques and present some applications to the light meson sector.
• | Presentation)

• (Abstract |
  • Recent progress in the bound-state problem in continuum QCD has produced a consistent treatment of the nucleon and its resonances. These studies predict the presence of strong diquark correlations within baryons, whose impact on the nucleon elastic and transition form factors will be illustrated. The Roper resonance is found to be the nucleon’s first radical excitation and consists of a core of three dressed-quarks whose charge radius is 80% larger than the proton analogue. This core is complemented by a meson cloud which reduces the observed Roper mass by about 20%; however, the quark core is revealed to probes with Q² > 3M_N².
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• (Abstract |
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• (Abstract |
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