# Heavy neutrino production via $Z'$ at the lifetime frontier

## TL;DR

This paper explores the potential of various experiments to detect long-lived heavy neutrinos produced from a $Z'$ boson decay in a gauged $B-L$ model, highlighting the sensitivity of future detectors to neutrino mixing parameters.

## Contribution

It provides a comprehensive analysis of the sensitivity of multiple lifetime frontier experiments to heavy neutrinos from $Z'$ decays within current constraints, including novel reach estimates for future detectors.

## Key findings

- FASER 2 can detect neutrino mixing down to 10^{-4}
- CODEX-b and LHCb can reach mixing of 10^{-5}
- MATHUSLA can probe mixing as low as 10^{-7}

## 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.