Speaker
Dr
Victor Mokeev
(Thomas Jefferson National Accelerator Facility)
Description
Studies of the excited nucleon state ($N^*$) spectrum offer insight into the strong QCD dynamics underlying
baryon generation. In particular, they elucidate the symmetries of the strong interaction relevant for the
bound systems of three constituent quarks in the regime of large QCD-running coupling. The full spectrum
of nucleon resonances shaped the transition from a deconfined mixture of quarks and gluons to a hadron gas
in the few millisecond age of the Universe when the hadron mass was generated dynamically and quark-gluon
confinement emerged. These fundamental subjects are addressed in the search for the ``missing" baryon
states. Many of the nucleon resonances expected from LQCD and quark models based on SU(6)$\times$O(3)
spin-flavor-space symmetry have escaped experimental detection.
Experiments with the CLAS detector in Hall~B at JLab offer an excellent opportunity in the search for
``missing" baryon states from the data on most exclusive meson photo-/electroproduction channels relevant
in the $N^*$-excitation region. In this talk we will present results on the observation of several new nucleon
resonances from the global coupled-channel analysis of most exclusive photoproduction data measured at JLab,
ELSA, GRAAL, and MAMI, with a major impact from the CLAS results on $K\Lambda$, $K\Sigma$
photoproduction off protons. In addition, the combined studies of $\pi^+\pi^-p$ photo- and electroproduction
off proton data from CLAS have revealed the presence of the new $N'(1720)3/2^+$ baryon state. This new state,
together with the conventional $N(1720)3/2^+$ resonance, are required in order to describe the $\pi^+\pi^-p $
photo- and electroproduction off proton data with $Q^2$-independent nucleon resonance masses, and total and
partial hadronic decay widths to the $\pi\Delta$ and $\rho p$ final states.
Combined studies of the meson photo- and electroproduction off proton data will allow us to complete the
exploration of the excited nucleon state spectrum. The future studies of the $N^*$ spectrum with the new
CLAS12 detector will be focused on the search for new states of baryon matter, the so-called hybrid baryons,
with the glue as an active structural component.\footnote{The Southeastern Universities Research Association
(SURA) operates the Thomas Jefferson National Accelerator Facility for the United States Department of
Energy under Contract No. DE-AC05-84ER40150. This material is based upon work supported by the US Department
of Energy, Office of Science, Office of Nuclear Physics under Contract No DE-AC05-06OR23177 }
Primary author
Dr
Victor Mokeev
(Thomas Jefferson National Accelerator Facility)
Co-author
Dr
Volker Burkert
(Jefferson Lab)
