Measurement of the generalized polarizabilities of the proton at intermediate ${Q}^{2}$

Measurement of the generalized polarizabilities of the proton at intermediate $Q^{2}$

H. Fonvieille et al. (A1 Collaboration)

Phys. Rev. C 103, 025205 – Published 24 February 2021

Abstract

Background: Generalized polarizabilities (GPs) are important observables to describe the nucleon structure, and measurements of these observables are still scarce.

Purpose: This paper presents details of a virtual Compton scattering (VCS) experiment, performed at the A1 setup at the Mainz Microtron by studying the $e p \to e p γ$ reaction. The article focuses on selected aspects of the analysis.

Method: The experiment extracted the $P_{LL} - P_{TT} / ε$ and $P_{L T}$ structure functions, as well as the electric and magnetic GPs of the proton, at three new values of the four-momentum transfer squared $Q^{2}$ : 0.10, 0.20, and $0.45 {GeV}^{2}$ .

Results: We emphasize the importance of the calibration of experimental parameters. The behavior of the measured $e p \to e p γ$ cross section is presented and compared to the theory. A detailed investigation of the polarizability fits reveals part of their complexity, in connection with the higher-order terms of the low-energy expansion.

Conclusions: The presented aspects are elements which contribute to minimize the systematic uncertainties and improve the precision of the physics results.