Dr. rer. nat. Jan Michael Friedrich "The proton radius in high-energy muon-proton elastic scattering"

Thursday 28 May 2020, 09:30 → 10:30 Europe/Berlin

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The form factor of the proton and its first series expansion parameter, the proton radius, have been
a driving challenge since the beginning of hadron physics, and constitute one of the most fundamental quantities to understand nature. For its importance, it is surprising that the uncertainty on the proton radius is still on the level of 5%, which is apparently not driven by the apparative precision that allows since long measurements in the range of 1% accuracy. Different experimental techniques have delivered contradictory results, most recently the PRad measurement at JLab (2019) with respect to the largest data set obtained at MAMI (2010). Prior to PRad, line shifts in muonic atoms have pointed to a value in agreement with the theory expectation, which is unchanged since the dispersive analyses in the 1970s. In view of this contradictory situation, we propose a new measurement at the CERN-SPS M2 beamline with very different, and partly advantageous, systematics through high-energy elastic muon scattering off protons in a gaseous target allowing to detect the recoiling protons even at smallest momentum transfer that allows a new high-precision determination of the proton radius.