Light Dark Matter search in a beam-dump experiment: BDX at Jefferson Lab

Abstract

The Beam Dump eXperiment (BDX) aims to investigate the existence of light Dark Matter (DM) particles in the MeV-GeV mass range, theoretically well motivated but still barely explored. In this mass range BDX will be sensitive to large regions of DM parameter space, exceeding the discovery potential of existing and planned experiments by up to two orders of magnitude. BDX is an e--beam thick-target experiment, expected to run at Jefferson Lab, downstream of the Hall A beam dump, receiving up to 1022 electron-on-target (EOT). The detector is made of two main components: An electromagnetic calorimeter (Ecal), and a veto detector used to suppress the background. BDX will be sensitive to elastic and inelastic DM-electron scattering at the level of 10 counts per year, reaching the limit of the irreducible background due to beam-produced neutrinos. The expected signature of the DM interaction in the Ecal is a ~ GeV electromagnetic shower paired with a null activity in the surrounding active veto counters. In order to evaluate the background contributions two approaches were used: The cosmogenic background was extrapolated from results obtained with a prototype running at INFN-LNS (Italy), while the beam- related background was evaluated by GEANT4 Monte Carlo simulations. This paper describes the experimental setup and the results of the background studies along with the status and prospectives of the experiment.