Endothermic Z'-Portal Dark Matter: LZ-LHC Complementarity

Abstract

Motivated by the $2.6\sigma$ high-energy recoil event recently reported by the LUX-ZEPLIN (LZ) Collaboration, we consider an endothermic $Z^{\prime }$-portal Majorana dark matter framework and discuss the complementarity between the LZ event and LHC searches for a $Z^{\prime }$ resonance. As a concrete realization, we consider a gauged U(1) $B-L$ extension of the Standard Model. The phenomenology of the framework is essentially controlled by two free parameters: the U(1) $B-L$ gauge coupling $g_{BL}$ and the $Z^{\prime }$ boson mass $m_{Z^{\prime }}$. For a fixed $m_{Z^{\prime }}$, the observed dark matter abundance requires the dark matter mass to be near the $Z^{\prime }$ resonance, $m_{\mathrm{DM}}\sim m_{Z^{\prime }}/2$, and sets a lower bound on $g_{BL}$. Complementarily, LHC searches for a $Z^{\prime }$ resonance set an upper bound on $g_{BL}$. The parameter space allowed by the dark matter abundance and LHC constraints can account for the recent LZ event. The synergy between future $Z^{\prime }$ resonance searches at the High-Luminosity LHC and the LZ experiment may provide a test of this framework.

10 pages, 2 figures, figure 2 updated, new references added, typos corrected