The following listing gives the titles and abstracts for CLAS papers in refereed publications, in reverse chronological order. If a paper was released by the whole Collaboration then only the lead author is given.

Submitted Papers

• Two-Nucleon Momentum Distributions Measured in 3He(e,e'pp)n
  R. Niyazov, et al. (The CLAS Collaboration)
  (Submitted to The Physical Review Letters, August 15, 2003)

  Abstract
  We have measured the ³He(e,e'pp)n reaction at 2.2 GeV over a wide kinematic range. The kinematic energy distribution for the 'fast' nucleons (p > 250 MeV/c) peaks where two nucleons each have 20% or less and the third nucleon most of the transferred energy. These fast pp and pn pairs are back-to-back with little momentum along q(vec), indicating that they are spectators. Experimental and theoretical evidence indicates that we have measured distorted two-nucleon momentum distributions in ³He(e,e'pp)n by striking the third nucleon and detecting the spectator correlated pair.

• Observation of an Exotic S = +1 Baryon in Exclusive Photoproduction from the Deuteron
  S. Stepanayn, et al. (The CLAS Collaboration)
  (Submitted to The Physical Review Letters, July 16, 2003)

  Abstract
  An exclusive measurement of the reaction γ d ® K⁺K^-pn is reported from the CLAS collaboration at Jefferson Lab. A narrow peak, attributed to an exotic baryon with strangeness S = +1, is seen in the K⁺n invariant mass at 1543±5 MeV/c² with a measured half width that is consistant with the experimental resolution of the CLAS dectector (22 MeV FWHM). The statistical significance of the peak is 5.4±0.6 σ, for a Gaussian peak shape on top of a smooth background. This result is consistant with inclusive measurement of a narrow S = +1 baryon resonance reported by other experimantal groups.

• Measurement of the Spin Structure Functions in the Resonance Region for Q² from 0.15 to 1.6 GeV²
  R. Fatemi, et al. (The CLAS Collaboration)
  (Submitted to The Physical Review Letters, June 17, 2003)

  Abstract
  Double polarization asymmetries for the inclusive ep scattering were measured at Jefferson Lab using 2.6 and 4.3 GeV longitudinally polarized electrons incident on a longitudinally polarized NH₃ target in the CLAS detector. The polarized structure function g₁(x,Q²) was extracted throughout the nucleon resonance region and into the deep inelastic regime, for Q² = 0.15 - 1.64 GeV². The contributions to the first moment Γ(Q²) = ò g₁(x,Q²)dx were determined and, using a parameterization for g₁ in the unmeasured regions, the complete first moment was estimated over this Q² region. A rapid change in Γ is observed for Q² < 1 GeV², with a sign change near Q² = 0.29 GeV², the pQCD evolution scaling value. We attribute this to significant resonance contributions not explicitly included in the pQCD evolution.

• Hyperon Photoproduction in the Nucleon Resonance Region
  J. W. C. McNabb, et al. (The CLAS Collaboration)
  (Submitted to The Physical Review Letters; May 27, 2003)

  Abstact
  Cross sections and polarizations for the reactions γ + p ® K⁺ + Λ and γ + p ® K⁺ + Σ⁰ have been measured with high statistics and with good angular coverage for center-of-mass energies between 1.6 and 2.3 GeV. In the K⁺ Λ channel we confirm a structure near W=1.9 GeV at backward kaon angles, but out data show a more complex s- and u-channel resonanance structure than previously seen. This structure is present at forward and backward angles but not central angles, and its postion and width change with angle, indicating more than one resonance is playing a role. Rising back-angle cross section at higher energies and large positive polarization at backward angles are consistant with sizable s- or u-channel contributions. None of the model calculations we present can consistantly explain these aspects of the data.

• Measurement of Beam-Spin Asymmetries for e(pol)p ® e'π+ X in the Deeply Inelastic Regime

  (Sumbitted to Physical Review Letters)
  H. Avakian, et al. (The CLAS Collaboration)

  Abstract
  We report the first significant measurement of the beam-spin asymmetry in the electroproduction of positive pions above the baryon resonance region with data obtained using the CLAS detector at Jefferson Lab and a beam energy of 4.25 GeV. When the analysis is restricted to events for which the pion carries a large fraction of the virtual photon momentum, the amplitude of the measured sin(φ) modulation is 0.037 ± 0.006.

Accepted Papers

• Measurement of Polarized Structure Function sigma(LT') for p(e(vec),e'p)pi0 from single pi0 electroproduction in the Delta resonance region
  K. Joo, et al. (The CLAS Collaboration)
  ( The Physical Review C, Rapid Communication, August 22, 2003)

  http://arxiv.org/abs/nucl-ex/0301012

  Abstract
  The polarized longitudinal-transverse structure function sigma(LT') has been measured for the first time in the Delta(1232) resonance region at Q^2 = 0.40 and 0.65 GeV^2. Data for the p(e(vec),e'p)pi0 reaction were taken at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS) using longitudinally polarized electrons at an energy of 1.515 GeV. Evidence for interference between resonant and non-resonant amplitudes is discussed using a partial wave analysis. Comparison with previous beam asymmetry measurements at MAMI indicate a deviation from predicted Q^2 dependence of sigma(LT') using recent phenomenolgical models.

• Study of the Δ(1232) using single and double polarization asymmetries
  A. Biselli, et al. (The CLAS Collaboration)
  (Accepted by The Physical Review C, July 1, 2003)

  Abstract
  Measurement of the angular distribution of target and double spin asymmetries for the Δ⁺(1232) in the exclusive channel p(pol)(e(pol),e'p)π⁰ obtained at Jefferson Lab in the Q² range from 0.5 to 1.5 GeV²/c² are presented. Results of the asymmetries are compared with the unitary isobar model MAID, the dynamical model by Sato and Lee and the effective Lagrangian theory by R. Davidson and N. Mukhopadyay. Sensitivity to the different models was observed, particularly in relation to the description of the background terms E₀₊, S₀₊, M₁₊ and S_1-, on which the target asymmetry depends significantly.

Published Papers

• Observation of Nuclear Scaling in the A(e,e') Reaction at x_Bjorken > 1
  K. Sh. Egiyan, et al. (The CLAS Collaboration)
  The Physical Review C 68, 014313 (2003)

  Abstract
  The ratios of inclusive electron scattering cross sections of ⁴He, ¹²C, and ⁵⁶Fe to ³He have been measured for the first time. It is shown that these ratios are independent of x_Bjorken at Q² > 1.4 (GeV/c)² for x_Bjorken > 1.5, where the inclusive cross section depends primarily on the high momentum components of the nuclear wave function. The scaling was predicted by the Short Range Correlation (SRC) model. The values of these ratios in the scaling region are related to the relative probabilities of SRC in these nuclei. Our data demonstrate that for nuclei with A > 12 these probabilities are about 5 times larger than in the deuteron, while for ⁴He it is larger by a factor of only about 3.

• Measurement of ep -> e'p pi+ pi- and baryon resonance analysis
  Physical Review Letters 91 022002, (2003)
  
  M. Ripani, et al. (The CLAS Collaboration)

  Abstract
  The cross section for the reaction ep ® e' p π⁺ π^- was measured in the resonance region for 1.4 < W < 2.1 GeV and 0.5 < Q² < 1.5 GeV²/c², using the CLAS detector at Jefferson Laboratory.Data shows resonant structures not visible in previous experiments. The comparison of our data to a phenomenological prediction using available information on N^* and Δ states shows an evident discrepancy. A better description of the data is obtained either by a sizable change of the properties of the P₁₃(1720) resonance or by introducing a new baryon state, not reported in published analyses.

• Measurement of Inclusive Spin Structure Fuctions of the Deuteron with CLAS
  J. Yun, et al. (The CLAS Collaboration)
  The Physical Review C, 67, 055204 (2003)

  Abstract
  We report the results of a new measurement of the spin structure functions of the deuteron in the region of moderate momentum transfer (Q² = 0.27 - 1.3 (GeV²)) and final hadronic state mass in the resonance region (W = 1.08 - 2.0 GeV). We scattered a 2.5 GeV polarized continuous electron beam at Jefferson Lab off a dynamically polarized cryogenic solid state target (¹⁵ND₃) and detected the scattered electrons with the CEBAF Large Acceptance Spectrometer (CLAS). From our data, we extract the longitudinal double spin asymmetry A_|| and the spin structure function g₁^d. Our data are generally in good agreement with existing data from SLAC where they overlap, and they represent a substantial improvement in statistical precision. We compare our results with expectations for resonance asymmetries and extrapolated deep inelastic scaling results. Finally, we evaluate the first moment of the structure function g₁^d and study its approach to both the deep inelastic limit and large Q² and to the Gerasimov-Drell-Hearn sum rule at the real photon limit (Q² ® 0). We find that the first moment varies rapidly in the Q² range of our experiment and crosses zero around Q² ~ 0.65 (GeV/c)², indicating the dominance of the Δ resonance at these momentum transfers.

• The CEBAF Large Acceptance Spectrometer
  Nuclear Instruments and Methods 503/3, 513 (2003)
  B. Mecking, et al.

  Abstract
  A collaboration of 34 institutions has assembled the CEBAF Large Accceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. A ptogram of about 60 experiments will use this detector to study structures and interactions of mesons, nucleons, and nuclei using polarized and unpolarized electron and photon probes. A six-coil toroidal super-conducting magnet provides the magnetic field necessary to determine the momenta of charged particles as they are tracked using drift chambers. Cherenkov counters, time-of-flight scintillators and electromagnetic calorimeters provide particle identification. Fast triggering and high data acquisition rates allow operation at luminocities of 10³⁴/cm²/s.

• First Measurement of Transferred Polarization in the Exclusive e(pol)p ® e'K⁺Λ(pol) Reaction
  D. Carman, et al. The CLAS Collaboration
  Physical Review Letters 90, 131804 (2003)

  Abstract
  The first measurements of the trasferred polarization for the exclusive e(pol)p ® e'K⁺Λ(pol) reaction have been performed in Hall B at the Thomas Jefferson National Accelerator Facility using the CLAS spectrometer. A 2.567 GeV electron beam was used to measure the hyperon polarization over a range of Q² from 0.3 to 1.5 (GeV/c)² , W from 1.6 to 2.15 GeV, and over the full center-of-mass angular range of the K⁺ meson. Comparison with predictions of hadrodynamic models indicates strong sensitivity to the underlying resonance contributions. Contrary to the expectations of the widely used ³P₀ model of open-flavor hadron strong decays, our data suggest that the intermediate state s-sbar quark pair is produced with spins anti-aligned.

• A Complete Measurement of the F₂ Proton Structure Function in the Resonance Region and the Evaluation of the Moments
  M. Osipenko, et al. (The CLAS Collaboration)
  Physical Review D 67, 092001 (2003)

  Abstract
  We measured the inclusive electron-proton cross section in the nucleon resonance region (W < 2.5 GeV) at momentum transfers Q² below 4.5 (GeV/c)² with the CLAS detector. The large acceptance of CLAS allowed for the first time the measurement of the cross section in a simultaneously wide, two-dimennsional range of Q² and x, making it possible to perform an integration of the data at fixed Q² over the whole significant x-interval. From these data, we extracted the F₂ structure function and studied the Q² evolution of its moments, Mn(Q²), in order to estimate higher twist contributions. The statistical and systematic uncertainties of th JLAB data allow a precise extraction of the higher twists and therefore accurate theoretical predictions of the latter are now called for to allow a meaningful comparison.

• Photoproduction of the omega meson on the proton at large mementum transfer

  M. Battaglieri, et al. (The CLAS Collaboration)
  Physical Review Letters 90, 022002 (2003)

  Abstract
  The differential cross section, dσ/dt, for ω meson exclusive photoproduction on the proton above the resonance region (2.6 < W < 2.9 GeV) was measured up to a momentum transfer -t = 5 GeV² using the CLAS detector at Jefferson Laboratory. The ω channel was identified by detecting proton and pi+ in the final state and using missing mass technique. While the low momentum transfer region shows the typical diffreation pattern expected from Pomeron and Reggion-exchange, at large -t the differential cross section has a flat behavior. This feature can be explanied introducing quark interchange processes, beside the QCD-inspired two-gluon exchange.

• η photoproduction on the proton for photon energies from 0.75 to 1.95 GeV
  M. Dugger, et al. (The CLAS Collaboration)

  Physical Review Letters 89, 222002 (2002)

  Abstract
  Differential cross sections for the reaction γ p ® η p have been measured with a tagged photon beam for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified through missing mass reconstruction using kinematical information for the protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W = 1.75 GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S₁₁ resonance with mass ~1.8 GeV couples to the ηN channel.

  First Measurement of the Double Spin Asymmetry in e(pol)p(pol) ® e'pi+n in the Resonance Region
  (1-6-2002)
  Phys. Rev. Lett. 88, 082001 (2002); Erratum 88, 082001 2002)

  R. DeVita, et al. (The CLAS Collaboration)
  

  Abstract
  The first measurement of the double spin asymmetry for exclusive single π⁺ electroproduction from protons has been performed in Hall-B at the Thomas Jefferson National Accelerator Facility using CLAS. A 2.6-GeV polarized electron beam was incident on a polarized solid NH₃ target. The double spin asymmetry A_ep was measured in the resonance region for a range of momentum transfer squared, 0.35 < Q² < 1.5 GeV², and for a range of π⁺ center-of-mass polar angle, 0.25 < cos(θ_cm) < 1. Comparison with predictions of phenomenological models shows strong sensitivity to resonance contributions. Helicity-1/2 transitions are found to be dominant in the second and third resonance regions. The measured asymmetry is consistant with a faster rise with Q² of the helicity asymmetry A₁ for the F₁₅(1680) resonance than expected from the analysis of the unpolarized data.
  

• Q² Dependence of Quadrupole Strength in γ*p ® Δ ⁺(1232)...
  Physical Review Letters 88, 122001 (2002)
  

  K. Joo, et al. (The CLAS Collaboration)
  

  Abstract
  Models of baryon structure predict a small quadrupole deformation of the nucleon from residual tensor forces between the quarks or distortion from the pion cloud. Sensitivity to pion/quark degrees of freedom occurs through the Q² dependence of the magnetic (M₁₊) electric (E₁₊) and Coulomb (S₁₊) multipoles in the γ* p ® Δ ® p π⁰ transition. New measurements for E₁₊/M_{1 +} and S₁₊/M₁₊ are reported here over the range Q²=0.4 - 1.8 GeV², using a complete partial wave decomposition of the structure functions σ_T + ε_Lσ_L, σ_TT and σ_LT. Results show a clear preference for theoretical models incorporating pion rescattering.
  

• Photoproduction ofρ0 Meson on the Proton at Large Momentum Transfer /
  Physical Review Letters 87 172002 (2001)
  (LANL preprint: hep-ex/0107028)
  
  M. Battaglieri et al. (The CLAS Collaboration)
  

  The differential cross section, dσ/dt, for ρ⁰ meson photoproduction on the proton above the resonance region (2.6 < W < 2.9 GeV) was measured up to a momentum transfer -t = 5 GeV² using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The ρ⁰ channel was extracted from the measured two charged-pion cross section by fitting the π⁺π^- and p π⁺ invariant masses. The low momentum transfer region shows the typical diffractive pattern expected from Reggeon-exchange. The flatter behavior at large -t cannot be explained solely in terms of QCD-inspired two-gluon exchange models. The data indicate that other processes, like quark interchange, are important to fully describe ρ photoproduction.
  Supplemental CLAS analysis document cited in paper: postscript file
  
  

• Electroproduction of the Λ(1520) Hyperon
  (22-June-01)
  Physical Review C 64, 044601 (2001)
  (LANL preprint: hep-ex/0105029)
  
  S. Barrow et al. (The CLAS Collaboration)
  

  Abstract: The reaction ep ® e' K⁺ Λ(1520) with Λ(1520) ® p' K^- was studied at electron beam energies of 4.05, 4.25, and 4.46 GeV, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cos(θ_K+), φ_K+, Q², and W dependencies of Λ(1520) electroproduction are presented for the kinematic region 0.9 < Q² < 2.4 GeV² and 1.95 < W < 2.65 GeV. Also, the Q² dependence of the Λ(1520) decay angular distribution is presented for the first time. The cos(θ_K⁺) angular distributions suggest t-channel diagrams dominate the production process. Fits to the Λ(1520) t-channel helicity frame decay angular distributions indicate the m_z = ± 1/2 parentage accounts for about 60% of the total yield, which suggests this reaction has a significant contribution from t-channel processes with either K⁺ or longitudinal coupling to an exchanged K^*. The Q² dependence of the Λ(1520) production cross section is the same as that observed for Λ(1116) photo- and electroproduction.

  
  

• Observation of exclusive deeply virtual Compton scattering in polarized electron beam asymmetry measurements
  
  (10 October 2001)
  Physical Review Letters 87, 182002 (2001)
  (LANL preprint: hep-ex/0107043)
  
  S. Stepanyan et al. (The CLAS Collaboration)
  
  We report the first results of the beam spin asymmetry measured in the reaction e + p ® e + p + γ at a beam energy of 4.25 GeV. A large asymmetry with a sin(phi) modulation is observed, as predicted for the interference term of Deeply Virtual Compton Scattering and the Bethe-Heitler process. The amplitude of this modulation is alpha = 0.202 ± 0.028. In leading-order and leading-twist pQCD, the alpha is directly proportional to the imaginary part of the DVCS amplitude.
  
  
  
• Exclusive electroproduction of φ mesons at 4.2 GeV
  (23 October 2001)
  Physical Review C 63, 065205-1 (2001);64 059901(E)
  
  K. Lukashin, et al. (The CLAS Collaboration)
  

  We studied the exclusive reaction e p ® e' p' φ using the φ ® K⁺ K^- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CLAS detector at Jefferson Lab. Our experiment covers the range in Q² from 0.7 to 2.2 GeV², and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of phi production on the proton. Our measurement shows the expected decrease of the t-slope with the vector meson formation time cδτ below 2 fm. At cδτ = 0.6 fm, we measure b_φ = 2.27 ± 0.42 GeV^-2. The cross section dependence on W as W^{0.2±0.1} at Q² = 1.3 GeV² was determined by comparison with φ production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction.
  Link to Journal site
  

• The ep ® e'p(eta) reaction at and above the S11(1535) baryon resonance
  Physical Review Letters 86, 1702 (2001)
  
  R. Thompson, et al. (The CLAS Collaboration)
  New cross sections for the reaction ep ®e'pη are reported for the total center of mass energy W = 1.5 - 1.86 GeV and invariant momentum transfer Q² = 0.25 - 1.5 (GeV/c)². This large kinematic range allows extraction of important new information about response functions, photocouplings, and ηN coupling at W ~ 1.7 GeV; this is shown to come from interference between S and P waves and can be interpreted in terms of known resonances. Improved values are derived for the photon coupling amplitude for the S₁₁(1535) resonance.
  Link to Journal site
  

• The CLAS Cerenkov Detector
  
  Nuclear Instruments and Methods A 465, 414 (2001)
  
  G. Adams, V. Burkert, T. Carstens, V. Frolov, L. Houghtlin, G. Jacobs, M. Kossov, M. Klusman, B. Kross, M. Onuk J. Napolitano, J. W. Price, C. Riggs, M. Kossov, Y. Sharabian, A. Stavinsky, L. C. Smith, P. Stoler, W. Tuzel, K. Ullrich, A. Vlassov, A. Weisenberger, M. Witkowski, B. Wojtekhowski.
  

  The design, construction, and performance of the CLAS Cerenkov threshold gas detector at Jefferson Lab is described. The detector consists of 216 optical modules. Each module consists of 3 adjustable mirrors, of lightweight composite construction, a Winston light collecting cone, a 5-inch photomultiplier tube, and specially designed magnetic shielding.
  Link to Journal site
  

• The CLAS Start Counter
  Nuclear Instruments and Methods A 462, 484 (2001)
  
  S. Taylor, S. Ahmad, J. Distelbrink, G. S. Mutchler, E. Smith, T. Smith.
  

  The design, construction, and performance of a hexagonal-nose-cone shaped plastic scintillation counter system is described. This "Start Counter" is used as part of the trigger and to measure event start times for photon beam running with CLAS in Hall B at the Thomas Jefferson National Accelerator Facility. The Start Counter is constructed of three 3-mm thick coupled paddle scintillators and achieves a software-corrected time resolution of 260 ps. Each coupled-paddle scintillator operated without appreciable sagging up to ~1.2 MHz rate.
  Link to Journal site
  

• The CLAS Forward Electromagnetic Calorimeter
  Nuclear Instruments and Methods A 460, 239 (2001)
  
  M. Amarian, G. Asryan, K. Beard, W. Brooks, V.Burkert, T.Carstens, A.Coleman, R. Demirchyan, Yu. Efremenko, H. Egiyan, K. Egiyan, H. Funsten, V. Gavrilov, K. Gioanetti, R.M. Marshall, B. Mecking, H. Mkrtchan, R.C. Minehart, M. Ohandjanyan, Yu. Sharabian, L.C. Smith, S. Stepanyan, W.A. Stephens, T.Y. Tung, C. Zorn.

  The CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab utilizes six iron-free superconducting coils to provide an approximately toroidal magnetic field. The six sectors are instrumented individually to form six independent spectrometers. The forward region (8deg < (theta) < 45deg) of each sector is equipped with a lead-scintillator electromagentic sampling calorimeter (EC), 16 radiation lengths thick, using a novel triangular geometry with stereo readout. With its good energy and position resolution, the EC is used to provide the primary electron trigger for CLAS. It is also used to reject pions, reconstruct pi-0 and eta decays and detct neutrons, This paper treats the design, construction and performance of the calorimeter.
  Link to Journal site
  

• Photoproduction of φ(1020) Mesons on the Proton at Large Momentum Transfer
  Physical Review Letters 85, 4682 (2000)
  
  E. Anciant, et al. (The CLAS Collaboration)
  

  The cross-section for phi meson photoproduction on the proton has been measured for the first time up to a four-momentum transfer t = -4 GeV², using the CLAS detector at at Thomas Jefferson National Accelerator Facility. At low four-momentum transfer, the differential cross section is well-described by Pomeron exchange. At large four-momentum transfer, above -t = 1.8 GeV², the data support a model where the Pomeron is resolved into its simplest component, two gluons, which may couple to any quark in the proton and in the φ.
  Link to Journal site
  

• The CLAS Drift Chamber System
  Nuclear Instruments and Methods A 449 (2000) 81
  
  M.D. Mestayer, D.S. Carman, B. Asavapibhop, F.J. Barbosa, P. Bonneau, S.B. Christo, G.E. Dodge, T. Dooling, W.S. Duncan, S.A. Dytman, R. Feuerbach, G.P. Gilfoyle, V. Gyurjyan, K.H. Hicks, R.S. Hicks, C.E. Hyde-Wright, G. Jacobs, A. Klein, F.J. Klein, M.V. Kossov, S.E. Kuhn, R.A. Magahiz, R.W. Major, C. Martin, T. McGuckin, J. McNabb, R.A. Miskimen, J.A. Mueller, B.B. Niczyporuk, J. O'Meara, L.M. Qin, B.A. Raue, J. Robb, F. Roudot, R.A. Schumacher, D.J. Tedeschi, R.A. Thompson, D. Tilles, W. Tuzel. VanSyoc, M.F. Vineyard, L.B. Weinstein, G.R. Wilkin, A. Yegneswaran, J. Yun

  Experimental Hall B at Jefferson Laboratory houses the CEBAF Large Acceptance Spectrometer, the magnetic field of which is produced by a superconducting toroid. The six coils of this toroid divide the detector azimuthally into six sectors, each of which contains three large multi-layer drift chambers for tracking charged particles produced from a fixed target on the toroidal axis. Within the 18 drift chambers are a total of 35,148 individually instrumented hexagonal drift cells. The novel geometry of these chambers provides for good tracking resolution and efficiency, along with large acceptance. The design and construction challenges posed by these large-scale detectors are described, and detailed results are presented from in-beam measurements.
  

• Response to cosmic rays of the large-angle electromagnetic shower calorimeter of the CLAS detector
  Nuclear Instruments and Methods A 447 (2000) 424
  
  M. Anghinolfi, M. Battaglieri, P. Corvisiero, R. De Vita, E. Golovac, A. Longhi, V. Mokeev, G. Ricco, M. Ripani, V. Sapunenko,1, M. Taiuti, H. Avakian, N. Bianchi, E. De Sanctis, V. Gyuriyan, V. Muccifora, M. Mirazita, E. Polli, A.R. Reolon, F. Ronchetti, P. Rossi

  The measurement of the response of the large-angle electromagnetic shower calorimeter (LAC) of the CLAS detector to minimum ionizing particles is reported. The experimental set-up and the adopted procedures are described. The results of the light attenuation length in the calorimeter, the light output and the resolution of the interaction point reconstruction are discussed. The performances of the LAC match well with those required.

• The bremsstrahlung tagged photon beam in Hall B at JLab
  Nuclear Instruments and Methods A 440 (2000) 263
  
  D.I. Sober, Hall Crannell, Alberto Longhi, S.K. Matthews, J.T. O'Brien,B.L. Berman, W.J. Briscoe, Philip L. Cole, J.P. Connelly, W.R. Dodge, L.Y. Murphy, S.A.Philips, M.K. Dugger, D. Lawrence, B.G. Ritchie, E.S. Smith, James M. Lambert, E. Anciant, G. Audit, T. Auger, C. Marchand, M. Klusman, J. Napolitano, M.A. Khandaker, C.W. Salgado, and A.J. Sarty

  We describe the design and commissioning of the photon tagging beamline installed in experimental Hall B at the Thomas Jefferson National Accelerator Facility (JLab). This system can tag photon energies over a range from 20% to 95% of the incident electron energy, and is capable of operation with beam energies up to 6.1GeV. A single dipole magnet is combined with a hodoscope containing two planar arrays of plastic scintillators to detect energy-degraded electrons from a thin bremsstrahlung radiator. The first layer of 384 partially overlapping small scintillators provides photon energy resolution, while the second layer of 61 larger scintillators provides the timing resolution necessary to form a coincidence with the corresponding nuclear interaction triggered by the tagged photon. The definitions of overlap channels in the first counter plane and of geometric correlation between the two planes are determined using digitized time information from the individual counters. Auxiliary beamline devices are briefly described, and performance results to date under real operating conditions are presented. The entire photon-tagging system has met or exceeded its design goals.
  

• The time-of-flight system for CLAS
  Nuclear Instruments and Methods A 432 (1999) 265
  
  E.S. Smith, T. Carstens, J. Distelbrink, M. Eckhause, H. Egiyan, L. Elouadrhiri, J. Ficenec, M. Guidal, A.D. Hancock, F.W. Hersman, M. Holtrop, D.A. Jenkins, W. Kim, K. Loukachine, K. MacArthur, C. Marchand, B. Mecking, G. Mutchler, D. Schutt, L.C. Smith, T.P. Smith, S. Taylor, T.Y. Tung, A. Weisenberger, R.E. Welsh

  The time of flight system for the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Je!erson National Accelerator Facility is described. The system, covering an area of 206 m2 , is composed of scintillation counters 5.08 cm thick, 15 and 22 cm wide, and lengths which vary from 32 cm at the most forward angle to 450 cm at larger angles. All of the components of the system have been designed to optimize the time resolution. Event timing, achieved by leading-edge discrimination with time-walk correction, has been measured with cosmic rays, a laser pulser, and known particle interactions. The intrinsic time resolution varies from about 80 ps for the short counters to 160 ps for the longer counters. Reconstruction of interacting particles during the first period of operation yields an average time resolution for electrons of 163 ps.
  

• A composite thin vacuum window for the CLAS photon tagger at Jefferson lab
  Nuclear Instruments and Methods A 421 (1999) 23
  
  S.K. Matthews, Hall Crannell, J. T. O'Brien, D.I. Sober

  The construction of a thin vacuum window, currently in use on the CLAS photon tagging system at the Thomas Jefferson National Accelerator Facility, is described. A layer of woven Kevlar cloth supports a much thinner membrane of aluminized Mylar. Notable features of this particular window include its overall length (9.6m), and the fact that the entire load is supported by the epoxy seal with no mechanical clamping around the edges. Results from a diverse program of materials testing, including a clear dependence of leak rate on relative humidity, are also reported.
  

• The region one drift chamber for the CLAS spectrometer
  Nuclear Instruments and Methods A 419 (1998) 315
  
  D.S. Carman, S.A. Dytman, R. Magahiz, M.D. Mestayer, R.A. Miskimen, J.A. Mueller, R.A.Schumacher, D.J. Tedeschi, R.A. Thompson, and G.R. Wilkin

  The Region One detector is the innermost of three nested drift chamber packages of the CLAS spectrometer at Jefferson Laboratory. This detector, with 7776 drift cells, was optimized for the CLAS toroidal magnet geometry, and consists of six wedge-shaped sectors integrated into a single unit. Each sector has thin and relatively weak aluminum endplates which support the large mechanical loads from the wire tensions and associated readout hardware. The unusual feature of the detector is its self-supporting design, wherein the wire tensions of neighboring sectors balance each other without the use of massive structural support. We discuss the design criteria, mechanical components, and assembly procedures.
  

• Prototype studies and design considerations for the CLAS Region 2 drift chambers
  Nuclear Instruments and Methods A 411 (1998) 265
  
  L.M. Qin, B. A. Raue, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, T. D. Pyron, K. G. Vansyoc, L. B. Weinstein, J. Yun

  The CEBAF Large Acceptance Spectrometer (CLAS) has recently been commissioned in Hall B of the TJNAF. The six "Region 2" drift chambers built by Old Dominion University with technical support of Jefferson Lab, are located between the coils of the CLAS super-conducting toroidal magnet. The endplates were constructed from non-conducting fiberglass in order to eliminate eddy-current forces during possible magnet quenches. The non-conducting endplate allowed the use of compact wire connecting and signal transfer hardware, thus minimizing the loss of acceptnce of the Region 2 chambers. Wires were positined by flared trumpet-shaped metal feed throughs that were glued directly into precision holes drilled into the endplates. We report test results from two prototype chambers. A single-cell prototype proved general functionality of the endplate feedthrough design and showed that the active area of the chamber starts approximately 10 mm form the end of the sense wire. A 36-cell prototype achieved a tracking resolution of better than 150 microns with various gas mixtures.
  

• Construction update and drift velocity calibration for the CLAS drift chamber system
  Nuclear Instruments and Methods A 367 (1995) 316
  
  M. D. Mestayer, F. J. Barbosa, P. Bonneau, E. Burtin, S. Christo, G. Doolittle, S. A. Dytman, G. P. Gilfoyle, C.E. Hyde-Wright, A. Klein, M. V. Kossov, S. E. Kuhn, R. MAgahiz, R. A. Miskimen, L. Y. Murphy, J. E. O'Meara, T. D. Pyron, L. Qin, B. A Raue, R. A. Schumacher, W. Tuzel, L. B. Weinstein, and A. Yegneswaran

  We briefly describe the drift chamber system for the CLAS detector at CEBAF, concentrating on the method which will be used to calibrate the drift velocity function. We identify key features of the function which should apply to any small-cell drift chamber geometry in which the cathode and anode surfaces are wires. Using these ideas, we describe a simple method to compensate for variations in the drift velocity function due to environmental changes.
  

• A drift chamber system for a toroidal detector
  Nuclear Instruments and Methods A 323 (1992) 191
  
  F. J. Barbosa, S. Christo, C. Cuevas, G. Doolittle, D. C. Doughty, C. Hutton, D. Joyce, B. A. Mecking, M. D. Mestayer, B. Niczyporuk, J. E. O'Meara, D. Tilles, W. Tuzel, and A. Yegneswaran

  We present design details for drift chambers to be used in the CLAS detector at CEBAF. Novel features include nonparallel endplates fabricated from composite materials, a gas mixture which includes helium to reduce multiple scattering, low wire tensions, and a hexagonal cell layout. Magnetic field strength in the active region ranges from 0 to 2 T, and wire length varies from 10 to 300 cm. We discuss construction for the outer drift chambers.