ISR Experiment at A1-Collaboration

¹ Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, DE-55128 Mainz, Germany
² Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia

^* e-mail: miha.mihovilovic@ijs.si

Published online: 18 October 2019

Abstract

The discrepancy between the proton charge radius extracted from the muonic hydrogen Lamb shift measurement and the best present value obtained from the elastic scattering experiments, remains unexplained and represents a burning problem of today’s nuclear physics. In a pursuit of reconciling the puzzle an experiment is underway at MAMI, which exploits the radiative tail of the elastic peak to study the properties of electromagnetic processes and to extract the proton charge form factor $\left({{\displaystyle G}}_E^p\right)$ at extremely small Q². This paper reports on the latest results of the first such measurement performed at the three-spectrometer facility of the A1-Collaboration, which led to a precise validation of radiative corrections far away from elastic line and provided measurements of ${{\displaystyle G}}_E^p$ for 0.001 ≤ Q² ≤ 0.017 (GeV/c)².