# Virtual Compton Scattering measurements in the nucleon resonance region

## TL;DR

This paper presents new measurements of the proton's electric Generalized Polarizability and Coulomb quadrupole amplitude in the nucleon resonance region, providing insights into their dependence on momentum transfer and validating previous data models.

## Contribution

It introduces novel measurements of the proton's electric GP and Coulomb quadrupole amplitude using a different extraction method, enhancing understanding of nucleon structure.

## Key findings

- $ ext{Electric GP } ext{measured at } Q^2=0.20~(GeV/c)^2$ with specific value and uncertainties.
- First measurement of Coulomb quadrupole amplitude in the $N
ightarrow riangle$ transition.
- Results are consistent with previous pion electroproduction data, validating existing models.

## Abstract

We report on new measurements of the electric Generalized Polarizability (GP) of the proton $\alpha_E$ in a kinematic region where a puzzling dependence on momentum transfer has been observed, and we have found that $\alpha_E = (5.3 \pm 0.6_{stat} \pm 1.3_{sys})~10^{-4} fm^3$ at $Q^2=0.20~(GeV/c)^2$. The new measurements, when considered along with the rest of the world data, suggest that $\alpha_E$ can be described by either a local plateau or by an enhancement in the region $Q^2=0.20~(GeV/c)^2$ to $0.33~(GeV/c)^2$. The experiment also provides the first measurement of the Coulomb quadrupole amplitude in the $N \rightarrow \Delta$ transition through the exploration of the $p(e,e'p)\gamma$ reaction. The new measurement gives $CMR = (-4.4 \pm 0.8_{stat} \pm 0.6_{sys})~\%$ at $Q^2=0.20~(GeV/c)^2$ and is consistent with the results from the pion electroproduction world data. It has been obtained using a completely different extraction method, and therefore represents a strong validation test of the world data model uncertainties.