Excess of Tau events at SND@LHC, FASER$ν$ and FASER$ν$2

Abstract

During the run III of the LHC, the forward experiments FASERν and SND@LHC will be able to detect the Charged Current (CC) interactions of the high energy neutrinos of all three flavors produced at the ATLAS Interaction Point (IP). This opportunity may unravel mysteries of the third generation leptons. We build three models that can lead to a tau excess at these detectors through the following Lepton Flavor Violating (LFV) beyond Standard Model (SM) processes: (1) π + → µ + ν τ ; (2) π + → µ + ντ and (3) ν e + nucleus → τ + X.We comment on the possibility of solving the (g − 2) µ anomaly and the τ decay anomalies within these models. We study the potential of the forward experiments to discover the τ excess or to constrain these models in case of no excess. We then compare the reach of the forward experiments with that of the previous as well as next generation experiments such as DUNE. We also discuss how the upgrade of FASERν can distinguish between these models by studying the energy spectrum of the tau.

Tau neutrinos in the next decade: from GeV to EeV

“…In source and/or detector NSI (CC NSI), explicitly detecting the ν τ in the ND of an experiment such as DUNE can set the stringent bounds [151]. In addition, lepton flavor violating π + → μ + ν τ or π + → μ + ντ decay modes with branching ratios of O(10 −3 ), meditated by new heavy scalars, can also be probed at forward experiments such as FASERν by looking for a tau neutrino excess [152,153].…”