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

Abstract

We investigate the pair production of right-handed neutrinos mediated by a $Z^\prime$ from the meson decays at the FASER detector of the HL-LHC. The $Z^\prime$ can be either the additional gauge boson in 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 analyses the sensitivity to the masses of the heavy neutrinos, $m_N$, and active-sterile mixing, $V_{lN}^2$, of the FASER-2. In a background free scenario, FASER-2 is able to probe $V_{lN}^2 \approx 10^{-8}$ when $m_N \sim 0.2$ GeV, which is comparable to the current limits from the beam dump experiments for the right-handed neutrinos dominantly coupled to electron and muon flavours, and exceed three magnitude for tau. When comes to the $U(1)_s$ model, FASER-2 can probe $V_{lN}^2 \approx 10^{-10}$, which is better than the current limits in all three flavours. A proposed long-lived particle detector, FACET, is also studied, while no significant difference from FASER-2 is derived.Comment: 14 pages, 8 figure