Light, Long-Lived $B-L$ Gauge and Higgs Bosons at the DUNE Near Detector

Abstract

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 $Z{}^{\prime }$ and the associated $U(1{)}_{B-L}$-breaking scalar $\phi$ 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 $\phi$, the $Z{}^{\prime }$ 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 $\phi$ with gauge coupling to $Z{}^{\prime }$, the DUNE capability of discovering the gauge boson $Z{}^{\prime }$ can be significantly improved, even by one order of magnitude in $g_{BL}$, due to additional production from the decay $\phi \to Z{}^{\prime }Z{}^{\prime }$. The DUNE sensitivity is largely complementary to other long-lived $Z{}^{\prime }$ 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 $\phi$ itself at DUNE are to some extent weakened in presence of $Z{}^{\prime }$, compared to the case without the gauge interaction.

Comments: 17 pages plus 3 appendices, 7 figures, minor changes, more references, version published in JHEP