Quark model calculations of transition form factors at high photon virtualities

TL;DR

This paper uses a covariant quark model to calculate transition form factors for nucleon resonances at high photon virtualities, comparing results with experimental data mainly from Jefferson Lab.

Contribution

It provides new covariant quark model calculations of transition form factors at high $Q^2$, focusing on specific nucleon resonances and comparing with experimental data.

Findings

Valence quark contributions dominate at high $Q^2$.

Model estimates agree with Jefferson Lab data for certain resonances.

Provides predictions for higher mass resonances.

Abstract

We present calculations of $\gamma^\ast N \to N^\ast$ transition form factors, where $N$ is the nucleon and $N^\ast$ is a nucleon resonance, based on a covariant quark model. Our main focus is at high photon virtualities (large $Q^2$) where the valence quark degrees of freedom dominate the contributions to the transition form factors and helicity amplitudes. In that regime, the quark model estimates can be compared with the available data, particularly with the Jefferson Lab data at intermediate and large momentum transfer ($Q^2 >2$ GeV$^2$). The main focus is on the $\Delta(1232)3/2^+$, $N(1440)1/2^+$, $N(1535)1/2^-$ and $N(1520)3/2^-$ resonances, but estimates for other higher mass resonances are also discussed.