Standard model (of particle physics) is not complete, because it does not predict Dark Matter particles. Due to this incompleteness, any possible failure of the Standard model immediately attract a big attention.

Proton charge radius is determined by means of spectroscopy of ordinary (e-p) and muonic (mu-p) hydrogen and by means of electron-proton scattering. The e-p results are internally consistent and strongly disagree with the muonic value. If one reads the situation literally, the overall e-p to mu-p discrepancy is about 7-8 sigma, which indicates a violation of the lepton universality. I.e., e-p and mu-p interactions are somewhat different.

But that is if one reads the situation literally. In my talk I will review the present situation and will try to respond to the question whether we can really rely on the 7-8-sigma discrepancy.

Page created on January 13, 2015.