Covariant model for theγN→N(1535)transition at high momentum transfer

Abstract

A relativistic constituent quark model is applied to the N ! Nð1535Þ transition. The Nð1535Þ wave function is determined by extending the covariant spectator quark model, previously developed for the nucleon, to the S 11 resonance. The model allows us to calculate the valence quark contributions to the N ! Nð1535Þ transition form factors. Because of the nucleon and Nð1535Þ structure the model is valid only for Q 2 > 2:3 GeV 2 . The results are compared with the experimental data for the electromagnetic form factors F Ã 1 and F Ã 2 and the helicity amplitudes A 1=2 and S 1=2 , at high Q 2 .

Baryons as relativistic three-quark bound states

“…Another covariant approach is the covariant spectator model of Ref. [541], which has been actively explored for a range of observables including various elastic and transition form factors of octet and decuplet baryons [542][543][544][545][546][547]; a recent overview can be found in Ref. [548].…”

Electromagnetic Excitation of the Baryons Within the Covariant Spectator Formalism

“…N B are normalization constants, and β 1 and β 2 are momentum range parameters which regulate the short and long range behavior in configuration space. The analytic form (2), was initially chosen to reproduce the asymptotic form predicted by pQCD for the nucleon form factors (G E , G M ∼ 1/Q 4 ), but it also assures the expected pQCD behavior for the γ N → N * (1535) transition form factors [4]. Inspired by the relativistic quark models with an harmonic oscillator confinement [16], we used the same parameters β 1 and β 2 for the two cases, the N * (1535) and the nucleon.…”

“…where 0 I and 1 I are the diquark-isospin singlet and triplet states, X ρ and X λ are respectively the anti-symmetric and symmetric spin states of the diquark with respect to the exchange of its two quarks, and ψ S11 is a phenomenological function [4] giving the momentum distribution of the diquark in the N * (1535), in analogy with what was done for the nucleon case [1]. The scalar wave functions ψ B (B = N , S 11 ) are…”

“…To address this issue we have developed a model of the nucleon [1] within the covariant spectator theory (CST), which can be also extended, for instance, to the lowest lying nucleon excitation, the (1232) [2,3], the N * (1535) resonances [4], and also to the − baryon [5,6].…”

“…For that reason, the model is not used to predict the baryonic spectrum yet. The form of the covariant wave functions is chosen to satisfy the manifest baryon internal symmetries (flavor, spin, orbital angular momentum and parity), assuming a totally antisymmetric color wave function [1][2][3][4][5][6][7]. And the detailed shape of the wave function is encoded in parameters determined directly by the experimental data for the nucleon electromagnetic form factors, or the existing lattice data in some other cases.…”