Probing a $Z'$ gauge boson via neutrino trident scattering in the Forward Physics Facility at the LHC and FCC

Abstract

The study of neutrino physics at the Large Hadron Collider is already a reality, and a broad neutrino physics program is expected to be developed in forthcoming years at the Forward Physics Facility (FPF). In particular, the neutrino trident scattering process, which is a rare Standard Model process, is expected to be observed for the first time with a statistical significance of $5\sigma$ using the FASER$\nu$2 detector. Moreover, similar studies are expected to be performed in the proposed Future Circular Collider (FCC). Such perspectives motivate the investigation of the impact of New Physics on the predictions for the corresponding number of events. In this letter, we consider the $L_\mu - L_\tau$ model, which predicts an additional massive neutral gauge boson, $Z'$, that couples to neutrino and charged leptons of the second and third families, and estimate the production of a dimuon system in the neutrino trident scattering at the FASER$\nu$2 assuming different models for the incoming neutrino flux at the LHC and FCC energies. We derive the associated sensitivity and demonstrate that the FPF@LHC is not able to improve the current bounds on the $L_\mu - L_\tau$ model, while a future measurement of the dimuons produced in neutrino trident events in the FPF@FCC will extend the coverage of the parameter space in comparison to previous experiments.