Electroexcitation of the $\Delta^{+}(1232)$ at low momentum transfer

TL;DR

This paper presents new low momentum transfer measurements of the $ ext{Δ}^+(1232)$ resonance, testing chiral effective field theory predictions and revealing discrepancies with constituent quark models, thus guiding future theoretical improvements.

Contribution

It provides the lowest momentum transfer data for the Coulomb quadrupole amplitude, extending understanding of mesonic cloud effects in nucleon resonances.

Findings

Disagreement with constituent quark model predictions.

Reasonable agreement with chiral effective field theory and lattice calculations.

Highlights need for refinement in theoretical models.

Abstract

We report on new p$(e,e^\prime p)\pi^\circ$ measurements at the $\Delta^{+}(1232)$ resonance at the low momentum transfer region. The mesonic cloud dynamics is predicted to be dominant and rapidly changing in this kinematic region offering a test bed for chiral effective field theory calculations. The new data explore the low $Q^2$ dependence of the resonant quadrupole amplitudes while extending the measurements of the Coulomb quadrupole amplitude to the lowest momentum transfer ever reached. The results disagree with predictions of constituent quark models and are in reasonable agreement with dynamical calculations that include pion cloud effects, chiral effective field theory and lattice calculations. The reported measurements suggest that improvement is required to the theoretical calculations and provide valuable input that will allow their refinements.