FASER2

Abstract:

The possibility that the Fermi scale is the only fundamental energy scale of Nature is under serious consideration at present, yet cosmic rays may already have provided direct evidence of new physics at a much higher scale. The recent detection of very high energy particles with no plausible astrophysical sources suggests that these originate from the slow decays of massive particles clustered in the halo of our Galaxy. Such particles had in fact been predicted to exist beforehand with mass and lifetime in the range required to explain the observations. I discuss recent work focussing on experimental tests of this speculative but exciting idea.

Abstract:

We interpret the KARMEN time anomaly as being due to the production of a (dominantly bino) neutralino with mass 33.9 MeV, which is the lightest supersymmetric particle but decays into 3 leptons through the violation of R-parity. For independent gaugino masses M_1 and M_2 we find regions in the (M_1, M_2, mu, tan beta) parameter space where such a light neutralino is consistent with all experiments. Future tests of this hypothesis are outlined.