Z′ mediated right-handed neutrinos from meson decays at the FASER

We investigate the pair production of right-handed neutrinos mediated by a Z′ mainly from the meson decays at the FASER detector of the HL-LHC. The Z′ can be the additional gauge boson in either the U(1)B−L or sterile ν-specific U(1)s model. Taking the gauge coupling or the kinetic mixing at the current limits, we analyze the sensitivity to the masses of the heavy neutrinos, MN, and active-sterile mixing, |VlN|2, of FASER2. In a background-free scenario, for the U(1)B−L case, FASER2 is able to probe |VlN|2≈10−8 when MN∼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 |VlN|2≈10−10, which is better than the current limits for at least one magnitude, in all three flavors. A proposed long-lived particle detector, FACET, is also studied, but no significant difference from FASER2 is derived. Published by the American Physical Society 2024