Z' Mediated right-handed Neutrinos from Meson Decays at the FASER

Abstract

We investigate the pair production of right-handed neutrinos mediated by a $Z^{\prime }$ mainly from the meson decays at the FASER detector of the HL-LHC. The $Z^{\prime }$ can be the additional gauge boson in either the $U(1{)}_{B-L}$ or sterile $\nu$-specific $U(1{)}_s$ model. Taking the gauge coupling or the kinetic mixing at the current limits, we analyse the sensitivity to the masses of the heavy neutrinos, $M_N$, and active-sterile mixing, $|V_{lN}{|}^2$, of the FASER2. In a background free scenario, for the $U(1{)}_{B-L}$ case, FASER2 is able to probe $|V_{lN}{|}^2\approx 10^{-8}$ when $M_N\sim 0.3$ GeV, which is comparable to the current limits from the beam dump experiments. When comes to the $U(1{)}_s$ model, FASER2 can probe $|V_{lN}{|}^2\approx 10^{-10}$, which is better than the current limits for at least one magnitude, in all three flavours. A proposed long-lived particle detector, FACET, is also studied, while no significant difference from FASER2 is derived.

Comments: 14 pages, 8 figures, matches the pulished version in PRD