Measurement of the generalized polarizabilities of the proton at intermediate Q2

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 ep→epγ reaction. The article focuses on selected aspects of the analysis. Method: The experiment extracted the PLL-PTT/ϵ and PLT structure functions, as well as the electric and magnetic GPs of the proton, at three new values of the four-momentum transfer squared Q2: 0.10, 0.20, and 0.45GeV2. Results: We emphasize the importance of the calibration of experimental parameters. The behavior of the measured ep→epγ 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.