The proton radius puzzle, which surfaced over the past decade from a discrepancy of the proton charge radius measured with muonic hydrogen and electronic probes has challenged our basic understanding of the proton. Ideas to resolve the puzzle involve either beyond standard model physics, novelaspects of conventional physics, or issues in extracting the radius from the experimental data. None of these ideas is generally accepted, however, as the explanation for the puzzle. There are a number of experiments that aim to resolve the puzzle. Among those, the MUon Scattering Experiment (MUSE) at PSI is particularly interesting because it tries to determine the proton radius through μp scattering, which has not been done so far, simultaneously with ep scattering, in addition to performing these reactions with positive and negative leptons. The current status of the proton radius puzzle and the power of the MUSE experiment to resolve the puzzle will be discussed.
Miriam Diamond