NSTAR 2001 Proceedings of the Workshop on . The Physics of Excited Nucleons ^S^*?ft D. Drechsel & L. Tiator World Scientific NSTAR 2001 Proceedings of the Workshop on The Physics of Excited Nucleons [...]... the data 9 Summary The study of nucleon resonances using quark models is more than simply stamp collecting: we are exploring the consequences of QCD for the spectrum and decay of baryons; identifying the important degrees of freedom for the description of the majority of hadrons; and discovering the nature of the properties and interactions of those degrees of freedom Progress hinges on the solution... most of the deformation can be attributed to the asymmetric coupling of the meson cloud to the spin of the nucleon In the spherical quark model of the nucleon, the N — A excitation is a • pure M l {Mx'+ ) transition The resonant quadrupole multipoles E2 {Ex'+ ) and C2 {S1+ ) contain the pertinent information It has become standard practice to quote experimental and theoretical results in terms of the. .. understand the structure of hadrons and the intricate dynamics of their constituents It is the subject of investigations at every medium energy electron accelerator A brief overview of the field is presented, followed by a presentation of the Bates N—>A program 1 Introduction The possibility of nucleon deformation raised more than 20 years ago 1 still remains an open one The presence of resonant quadrupole... model consistent with a chiral model of the nucleon Deficiencies of the models that emerge as a result of the comparison with the data are rectified by re-adjustments of the parameters and/or by modifying the phenomenology This results in an improved understanding 14 of the underlying physics and gradual reduction of the model error For the H(e, e'p)7 channel the new dispersion theory 16 of the Mainz... that the A3/2"(1520) - Al/2~(1405) splitting may also have the same source 6 Hybrid Baryons Identification of hybrid baryons is complicated by the fact that they have the same quantum numbers as conventional three-quark excitations, and so should mix with conventional excitations Their identification is also some- 6 what model dependent, as it relies on the separation of the gluon and quark degrees of. .. theory 16 of the Mainz group, taken in conjunction with the previous work of Vanderhaeghen et al 17 allows to addresses the physics of "deformation" and of nucleon polarizabilities in the region above pion threshold simultaneously Of particular importance to the field is the prediction of the Dynamical Model 18,19 and of Sato and Lee 14 that most of the responses and the REM and RSM exhibit a distinct structure... determination » of the cross section in "parallel kinematics" a0, of the LT-asymmetry, ALT, and response RLT and the measurement of the induced proton polarization Pn Pn is proportional to the R^T response and it would be identically zero in the absence of background It was found 12 to be -0.397 ± 0.055 ± 0.009 which established the importance of the background contributions The coincident cross section in... based on a spectrum-generating algebra 4 describes excited states in terms of collective excitations of string-like objects which carry the quark quantum numbers, with radial excitations arising from rotations and vibrations of these strings As the degrees of freedom are extended, there are more excited states, some of which would be described in other models as excitations of the confining glue The constituent... lighter of the two Su states at 1535 MeV and the small Nr] width for the heavier state at 1650 MeV, which can be explained as due to mixing between the quark-spin-1/2 and 3/2 states caused by the tensor interaction of the strength implied by the contact interaction 10 Although there are also spin-orbit interactions arising from the Thomas precession of the quarks in the confining potential, and there... cancellation of these with the OGE spin-orbit interactions, the spin-orbit interactions which accompany the contact and tensor interactions in the nonrelativistic model cause splittings which are unphysically large A variational calculation in a large basis allows the use of a relativistic kinetic energy and parametrized relativistic corrections to the potentials of the kind expected from examining the OGE . Proceedings of the Workshop on The Physics of Excited Nucleons