Baryon resonances and their properties from the CLAS data
M. Ripani (Genua)
Photoproduction and electroproduction experiments on the nucleon provide a clean probe of nucleon structure since the electromagnetic interaction is well understood. In particular, the matrix elements for gamma N . N*, Δ* transitions to non-strange excited baryon states, commonly called the photon
coupling amplitudes, are sensitive to the nucleon and N* quark-level wave function. Therefore the photon couplings provide fundamental information on how quarks are bound into baryons and are sensitive to the basic interaction symmetries. These amplitudes have traditionally been calculated using quark models, and recently progress has been made in applying the techniques of Lattice QCD.
New, more extensive and precise experimental measurements are currently being carried on at different facilities, with the aim of improving our knowledge of a number of different baryon resonances in several different final states.
At Jefferson Laboratory, the 6 GeV CW, polarized electron beam provides a powerful microscope for probing hadron structure at the confinement scale. In Hall B, the CLAS detector provides the large kinematic coverage for charged particles and good momentum resolution necessary to identify and separate different hadronic final states from baryon resonance decay and to measure the angular distribution of the products, thereby allowing access to the partial wave content of the reaction, an essential feature in disentangling overlapping resonant states.
The main body of the data from CLAS will be illustrated, with emphasis on selected results.