Speaker
Description
The proton charge radius is one of the most basic characteristics of the nucleons and is crucial for many applications such as the determination of the Rydberg constant, for QED tests, etc. Its determination is a hot topic in several physics communities as it has been reported close to 0.84 fm or 0.88 fm using electron scattering, atomic and muonic hydrogen spectroscopy. The proton charge radius is obtained from the cross section of the elastic lepton proton scattering at low momentum transfer Q2. At RARIS, we are conducting the most reliable measurement of the proton charge radius with electron proton scattering during the ULQ2 (Ultra-Low Q2) experiment using the world’s lowest energy beam for electron scattering. The main specificities of the ULQ2 experiment are the low beam energy and the use of a plastic CH2 target that allows the absolute normalization of the hydrogen to the carbon scattering cross-section. The new beam line as well as the twin spectrometers have been commissioned and the measurement of the detector efficiency is already complete. Most of the data taking for the proton charge radius measurement is finished and the analysis to determine the proton radius is underway.
