Constraining neutrinophilic mediators at FASER$\nu$, FLArE and FASER$\nu$2

TL;DR

This paper investigates how collider neutrino experiments like FASERν, FLArE, and FASERν2 can constrain neutrinophilic mediators of various spins and masses, providing new bounds and sensitivities beyond existing limits.

Contribution

It offers the first analysis of neutrinophilic mediator constraints using collider neutrino data and explores future sensitivities at upcoming facilities.

Findings

Current FASERν data constrains vector mediators around 0.2 GeV.

Future experiments can improve bounds on scalar and vector mediators.

Constraints on scalar mediators can reach 0.08 GeV with charge identification.

Abstract

High energy collider neutrinos have been observed for the first time by the FASER$\nu$ experiment. The detected spectrum of collider neutrinos scattering off nucleons can be used to probe neutrinophilic mediators with GeV-scale masses. We find that constraints on the pseudoscalar (axial vector) neutrinophilic mediator are close to the scalar (vector) case since they have similar cross section in the neutrino massless limit. We perform an analysis on the measured muon spectra at FASER$\nu$, and find that the bounds on the vector mediator from the current FASER$\nu$ data are comparable to the existing bounds at $m_{Z^\prime}\approx 0.2$ GeV. We also study the sensitivities to a neutrinophilic mediator at future Forward Physics Facilities including FLArE and FASER$\nu$2 by using both the missing transverse momentum and the charge identification information. We find that FLArE and FASER$\nu$2 can impose stronger bounds on both the scalar and vector neutrinophilic mediators than the existing bounds. The constraints on the scalar mediator can reach 0.08 (0.1) for $m_\phi\lesssim1$ GeV with (without) muon charge identification at FASER$\nu$2.