Bonn 2020 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 42: Hadron Structure and Spectroscopy VIII
HK 42.2: Group Report
Thursday, April 2, 2020, 14:30–15:00, J-HS A
Proton radius measurement in high-energy muon scattering at COMPASS — •Martin Hoffmann for the COMPASSplusplus/AMBER working group — Universität Bonn, Helmholtz-Institut für Strahlen- und Kernphysik, Bonn, Germany
The proton radius can be determined either by measuring the slope of the electric form factor via elastic lepton-proton scattering at low squared four-momenta Q2 or by laser spectroscopy of hydrogen. Previous measurements of elastic electron-proton scattering and laser-spectroscopy of muonic hydrogen yielded contradicting results, which is known as the proton radius puzzle. In order to contribute to its solution, we propose a measurement using high-energy muon-proton elastic scattering at the M2 beam line of CERN’s super proton synchrotron in 2022. A scattering experiment using muons instead of electrons is interesting for two reasons: (a) it has different systematic uncertainties and (b) it can test for lepton-flavour effects as a possible explanation of the puzzle. The transferred momentum to the proton will be determined using an active-target time projection chamber (TPC) filled with high-pressure hydrogen, yielding a high-precision measurement of Q2. In order to over-constrain the reaction, the muon kinematics will be measured by the COMPASS spectrometer extended by precision silicon pixel detectors surrounding the hydrogen TPC. We present results from a test measurement in 2018 and plans for the final setup based on on-going Monte Carlo simulations. We also discuss the resolution on the proton radius that we plan to achieve.
Supported by BMBF.