Beam-helicity asymmetry measurements in the Virtual Compton Scattering reaction in the g*N-Delta transition at Q2=0.20 (GeV/c)^2

TL;DR

This paper reports new measurements of beam-helicity asymmetries in virtual Compton scattering at low Q2, providing insights into proton structure and nucleon excitation amplitudes, with results aligning well with dispersion-relation calculations.

Contribution

First measurement of beam-helicity asymmetry in VCS at Q2=0.20 GeV^2 in the Delta resonance region, enhancing understanding of proton GPs and nucleon excitation amplitudes.

Findings

Asymmetries well described by dispersion-relation calculations

Data shows high sensitivity to proton generalized polarizabilities

Results suggest future high-precision measurements can improve theoretical constraints

Abstract

We report on new beam-helicity asymmetry measurements (A_h) of the H(\vec{e},e'p)\gamma reaction in the Delta(1232)$ resonance at Q2=0.20 (GeV/c)2. The measurements were performed at MAMI and were carried out simultaneously with the measurement of the H(\vec{e},e'p)\pi^0 reaction channel. It is the lowest Q2 for which the $A_h$ for the virtual Compton scattering (VCS) reaction has been measured in the first resonance region. The measured asymmetries have been compared and have been found to be well described by dispersion-relation (DR) calculations for VCS. The sensitivity of the data to the Generalized Polarizabilities (GPs) of the proton and to the amplitudes associated with the nucleon excitation to the Delta(1232) has been explored through the DR formalism. The measured asymmetries have been found to exhibit a much higher sensitivity to the GPs while it is suggested that future measurements of higher statistical precision will offer stronger constraints to theoretical calculations and will provide valuable insight towards a more complete understanding of the GPs of the proton and of the pi-N amplitudes.