The low-energy $U(1)_{B-L}$ gauge symmetry is well-motivated as part of beyond Standard Model physics related to neutrino mass generation. We show that a light $B-L$ gauge boson $Z{}$ and the associated $U(1)_{B-L}$-breaking scalar $varphi$ can both be effectively searched for at high-intensity facilities such as the near detector complex of the Deep Underground Neutrino Experiment (DUNE). Without the scalar $varphi$, the $Z{}$ can be probed at DUNE up to mass of 1 GeV, with the corresponding gauge coupling $g_{BL}$ as low as $10^{-9}$. In the presence of the scalar $varphi$ with gauge coupling to $Z{}$, the DUNE capability of discovering the gauge boson $Z{}$ can be significantly improved, even by one order of magnitude in $g_{BL}$, due to additional production from the decay $varphi to Z{}Z{}$. The DUNE sensitivity is largely complementary to other long-lived $Z{}$ searches at beam-dump facilities such as FASER and SHiP, as well as astrophysical and cosmological probes. On the other hand, the prospects of detecting $varphi$ itself at DUNE are to some extent weakened in presence of $Z{}$, compared to the case without the gauge interaction.
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