Search for strongly interacting dark matter at Belle II

Abstract

A small component of dark matter (DM) that is strongly interacting with the standard model sector is consistent with various experimental observations. Despite the small abundance, strongly interacting DM can lead to pronounced signals in DM direct detection experiments. We study Belle II sensitivity on strongly interacting DM that has a MeV-GeV mass and couples with electrons. By taking into account the substantial interactions between DM and electrons within detectors, we compute the “ceiling” of the monophoton signature at Belle II, beyond which the monophoton channel loses its sensitivity, and visible electromagnetic calorimeter (ECL) clusters due to DM scatterings assume significance. We study two ECL signatures for strongly interacting DM: the monocluster and the dicluster channels. To carry out detailed calculations and to compare with other constraints, we consider DM models with light mediators, as they naturally lead to sizable interaction cross sections. We compute exclusion regions for the dicluster, monocluster, and monophoton channels. We find that Belle II (with currently accumulated data of 362 fb−1) can rule out a significant portion of the parameter space above the ceilings of the constraints from various DM direct detection and neutrino experiments, for the vector mediator case with mass ≳10 MeV. Belle II also offers superior constraints on new light particles compared to primordial black hole (PBH) for the scalar mediator with mass ≳10 MeV. Published by the American Physical Society 2024