Pion electro-production in the Roper region in chiral quark models

Abstract

We present a method to calculate pion electro-production amplitudes in a coupled-channel framework incorporating quasi-bound quark-model states. The method offers a clear prescription how to extract the resonant part of the amplitudes, even in the presence of different decay channels and a strong mixing of neighbouring resonances. The method is applied to the calculation of the M1− and the S1− amplitudes in the P11 partial wave in a simple chiral quark model. A good agreement with the observed M1− amplitude is found with a significant contribution from the pion cloud. The same effect is also prominent in the S1− amplitude but a rather uncertain data prevent us to draw a definitive conclusion.

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

“…Now model predictions can be compared to the new high-quality photo-and electroproduction data [1][2][3]. Updated versions [25][26][27][28] …”

Valence quark contributions for the γ*N→N(1440) form factors from light-front holography

“…The gap between valence quark models and the data at low Q 2 has been interpreted as the manifestation of the meson cloud effects [3,4,7,10]. When the meson cloud contributions are included in quark models the estimates approach the data [11][12][13][14][15][16].…”

“…Those decay widths are also difficult to explain in the context of a quark model. The meson cloud dressing helps to explain the Nð1440Þ → γN width, where the contributions associated with baryonmeson-meson states play an important role [14,15,19,21].…”

New results from the studies of theN(1440)1/2+, N(1520)3/2Mokeev1, Burkert2, Carman3 et al. 2016Phys. Rev. C935910View full textAdd to dashboardCite

“…Some quark models that have been developed [44][45][46][47][48] take into account the contribution from both mesonbaryon and quark degrees of freedom to the structure of excited nucleon states. Implementation of meson-baryon degrees of freedom allowed for a considerably improved description of the CLAS results on the N (1440)1/2 + and N (1520)3/2 − γ v pN * electrocouplings at photon virtualities Q 2 < 1.0 GeV 2 , while simultaneously retaining a good description of these results for Q 2 > 2.0 GeV 2 .…”