Heavy neutrino production via $Z^{\prime }$ at the lifetime frontier

Abstract

We investigate the pair production of right-handed neutrinos from the decay of an additional neutral $Z^{\prime }$ boson in the gauged $B-L$ model. Taking into account current constraints on the $Z^{\prime }$ mass and the associated gauge coupling $g_1^{\prime }$, we analyse the sensitivity of proposed experiments at the lifetime frontier, FASER 2, CODEX-b, MATHUSLA as well as a hypothetical version of the MAPP detector to a long lived heavy neutrino $N$ originating in the decays of the $Z^{\prime }$. We further complement this study with determining the reach of LHCb and a CMS-type detector for the high-luminosity LHC run. We demonstrate that in a background free scenario with $g_1^{\prime }=10^{-3}$ near the current limit, FASER 2 is sensitive to the active-sterile neutrino mixing down to $V_{\mu N}\approx 10^{-4}$, while a reach of $V_{\mu N}\approx 10^{-5}$ can be obtained for CODEX-b and LHCb, in a mass regime of $m_N\approx 5-20$ GeV and $m_{Z^{\prime }}\approx 20-70$ GeV. Finally, MATHUSLA can probe $V_{\mu N}\approx 10^{-7}$ and cover the mixing regime expected in a canonical seesaw scenario of light neutrino mass generation.

Comments: 20 pages, 6 figures, matches published version