  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.
