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 -> ep gamma reaction. The article focuses on selected aspects of the analysis. Method: The experiment extracted the P-LL - P-TT/epsilon and P-LT 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 GeV2. Results: We emphasize the importance of the calibration of experimental parameters. The behavior of the measured ep -> ep gamma 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.

Automated summary

This paper presents details of a virtual Compton scattering experiment at the Mainz Microtron, focusing on extracting electric and magnetic GPs of the proton, and calibration of experimental parameters. Results show the importance of calibration and comparison with theory, as well as the complexity of polarizability fits and their connection with low-energy expansion.