Virtual Compton Scattering measurements in the $\gamma^* N\to \Delta$ transition

TL;DR

This paper presents new low-Q^2 virtual Compton scattering measurements in the Δ(1232) resonance, confirming theoretical models and aligning with pion electroproduction data, thus advancing understanding of nucleon resonance structure.

Contribution

First VCS measurements at such low Q^2 in the Δ region, validating dispersion relation models with pion electroproduction inputs.

Findings

VCS cross sections match dispersion relation calculations

Resonant magnetic dipole amplitude agrees with pion data

Results confirm compatibility of VCS and pion electroproduction analyses

Abstract

We report on new H$(e,e^\prime p)\gamma$ measurements in the $\Delta(1232)$ resonance at $Q^2=0.06$ (GeV/c) carried out simultaneously with H$(e,e^\prime p)\pi^0$. It is the lowest $Q^2$ for which the virtual Compton scattering (VCS) reaction has been studied in the first resonance region. The VCS measured cross sections are well described by dispersion-relation calculations in which the multipole amplitudes derived from H$(e,e^\prime p)\pi^0$ data are used as input, thus confirming the compatibility of the results. The derived resonant magnetic dipole amplitude $M^{3/2}_{1+} = (40.60 \pm 0.70_{stat+sys})(10^{-3}/m_{\pi^+})$ at $W=$ 1232 MeV is in excellent agreement with the value extracted from H$(e,e^\prime p)\pi^0$ measurements.