ZBL′portal dark matter and LHC Run-2 results

Abstract

We consider a concise dark matter scenario in the minimal gauged $B\ensuremath{-}L$ extension of the standard model (SM), where the global $B\ensuremath{-}L$ (baryon number minus lepton number) symmetry in the SM is gauged, and three generations of right-handed neutrinos and a $B\ensuremath{-}L$ Higgs field are introduced. Associated with the $B\ensuremath{-}L$ gauge symmetry breaking by a VEV of the $B\ensuremath{-}L$ Higgs field, the seesaw mechanism for generating the neutrino mass is automatically implemented after the electroweak symmetry breaking in the SM. In this model context, we introduce a ${Z}_{2}$-parity and assign an odd parity for one right-handed neutrino while even parities for the other fields. Therefore, the dark matter candidate is identified as the right-handed Majorana neutrino with odd ${Z}_{2}$ parity, keeping the minimality of the particle content intact. When the dark matter particle communicates with the SM particles mainly through the $B\ensuremath{-}L$ gauge boson (${Z}_{BL}^{\ensuremath{'}}$ boson), its relic abundance is determined by only three free parameters, the $B\ensuremath{-}L$ gauge coupling (${\ensuremath{\alpha}}_{BL}$), the ${Z}_{BL}^{\ensuremath{'}}$ boson mass (${m}_{{Z}^{\ensuremath{'}}}$) and the dark matter mass (${m}_{\mathrm{DM}}$). With the cosmological upper bound on the dark matter relic abundance we find a lower bound on ${\ensuremath{\alpha}}_{BL}$ as a function of ${m}_{{Z}^{\ensuremath{'}}}$. On the other hand, we interpret the recent LHC Run-2 results on search for ${Z}^{\ensuremath{'}}$ boson resonance to an upper bound on ${\ensuremath{\alpha}}_{BL}$ as a function of ${m}_{{Z}^{\ensuremath{'}}}$. Combining the two results we identify an allowed parameter region for this ``${Z}_{BL}^{\ensuremath{'}}$ portal'' dark matter scenario, which turns out to be a narrow window with the lower mass bound of ${m}_{{Z}^{\ensuremath{'}}}>2.5\text{ }\text{ }\mathrm{TeV}$.