Initial state radiation experiment at MAMI

¹ Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, DE-55128 Mainz, Germany
² Department of Physics, University of Zagreb, HR-10002 Zagreb, Croatia
³ Clermont Université, CNRS/IN2P3, LPC, BP 10448, F-63000 Clermont-Ferrand, France
⁴ Jožef Stefan Institute, SI-1000 Ljubljana, Slovenia
⁵ Department of Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia

^a e-mail: miham@kph.uni-mainz.de

Published online: 6 May 2014

Abstract

In an attempt to contribute further insight into the discrepancy between the Lamb shift and elastic scattering determinations of the proton charge radius, a new experiment at MAMI is underway, aimed at measuring proton form-factors at very low momentum transfers by using a new technique based on initial state radiation. This paper reports on the conclusions of the pilot measurement performed in 2010, whose main goal was to check the feasibility of the proposed experiment and to recognize and overcome any obstacles before running the full experiment. The modifications to the experimental apparatus are then explained which significantly improved the quality of data collected in the full scale experiment, which was successfully executed in August 2013. At the end first findings of the new experiment are discussed.