Electromagnetic structure of the nucleon and the Roper resonance in a light-front quark approach

A relativistic light-front quark model is used to describe both the elastic nucleon and nucleon-Roper transition form factors in a large Q2 range, up to 35 GeV2 for the elastic and up to 12 GeV2 for the resonance case. Relativistic three-quark configurations satisfying the Pauli exclusion principle on the light-front are used for the derivation of the current matrix elements. The Roper resonance is considered as a mixed state of a three-quark core configuration and a molecular N+sigma hadron component. Based on this ansatz we obtain a realistic description of both processes, elastic and inelastic, and show that existing experimental data are indicative of a composite structure of the Roper resonance.Comment: 19 page

Electroproduction of lightest nucleon resonances up to Q*2=12 GeV*2 in quark models at light front

The lightest nucleon resonances are described at light front as mixed states of the 3q cluster (“quark core”) possessing a definite value of the inner orbital momentum L = 0,1 and a hadron molecular state, N+σ or Λ+K. Helicity amplitudes of the resonance electroproduction off the proton are calculated at large Q2 up to 12 GeV2 and compared to the last CLAS data. At this basis we have estimated the probability of quark core in lightest nucleon resonances and predicted the high Q2 behaviour of the resonance electrocoupling

Role of the rho meson in the description of pion electroproduction experiments at JLab

We study the p(e,e' pi+)n reaction in the framework of an effective Lagrangian approach including nucleon, pi and rho meson degrees of freedom and show the importance of the rho-meson t-pole contribution to sigmaT, the transverse part of cross section. We test two different field representations of the rho meson, vector and tensor, and find that the tensor representation of the rho meson is more reliable in the description of the existing data. In particular, we show that the rho-meson t-pole contribution, including the interference with an effective non-local contact term, sufficiently improves the description of the recent JLab data at invariant mass W less 2.2 GeV and Q2 less 2.5 GeV2/c2. A ``soft'' variant of the strong piNN and rhoNN form factors is also found to be compatible with these data. On the basis of the successful description of both the sigmaL and sigmaT parts of the cross section we discuss the importance of taking into account the sigmaT data when extracting the charge pion form factor Fpi from sigmaL.Comment: 23 pages, 6 figures, accepted for publication in Phys. Rev.

Electroproduction of lightest nucleon resonances up to Q*2=12 GeV*2 in quark models at light front

The lightest nucleon resonances are described at light front as mixed states of the 3q cluster (“quark core”) possessing a definite value of the inner orbital momentum L = 0,1 and a hadron molecular state, N+σ or Λ+K. Helicity amplitudes of the resonance electroproduction off the proton are calculated at large Q2 up to 12 GeV2 and compared to the last CLAS data. At this basis we have estimated the probability of quark core in lightest nucleon resonances and predicted the high Q2 behaviour of the resonance electrocoupling