Dark Matter Search in a Beam-Dump eXperiment (BDX) at Jefferson Lab

Abstract

MeV-GeV dark matter (DM) is theoretically well motivated but remarkably unexplored. This proposal presents the MeV-GeV DM discovery potential for a ∼1 m 3 segmented CsI(Tl) scintillator detector placed downstream of the Hall A beam-dump at Jefferson Lab, receiving up to 10 22 electrons-on-target (EOT) in 285 days. This experiment (Beam-Dump eXperiment or BDX) would be sensitive to elastic DM-electron and to inelastic DM scattering at the level of 10 counts per year, reaching the limit of the neutrino irreducible background. The distinct signature of a DM interaction will be an electromagnetic shower of few hundreds of MeV, together with a reduced activity in the surrounding active veto counters. A detailed description of the DM particle χ production in the dump and subsequent interaction in the detector has been performed by means of Monte Carlo simulations. Different approaches have been used to evaluate the expected backgrounds: the cosmogenic background has been extrapolated from the results obtained with a prototype detector running at INFN-LNS (Italy), while the beam-related background has been evaluated by GEANT4 Monte Carlo simulations. The proposed experiment will be sensitive to large regions of DM parameter space, exceeding the discovery potential of existing and planned experiments in the MeV-GeV DM mass range by up to two orders of magnitude. 4We propose a beam-dump experiment to search for light (MeV-GeV) Dark Matter (DM). DM in this mass range is motivated by both experimental and theoretical considerations. On the theory side, simple extensions to the Standard Model (SM) can accommodate DM-SM interactions that yield the observed DM cosmological abundance. On the experimental side, such models also generically feature particles that explain the currently discrepant value of the muon's anomalous magnetic moment and resolve anomalies in astrophysical observations, while simultaneously evading cosmological and direct-production constraints.This experiment could be performed by placing a detector downstream of one of the JLab experimental Halls to detect DM particles that could be produced by the electron beam in the dump, pass through surrounding shielding material, and deposit visible energy inside the detector by scattering off various target particles or -if unstable -by decaying inside the detector volume. A new underground facility placed ∼ 20m downstream of the beam dump of the experimental Hall-A will host the detector, serving as a general-purpose facility for any future beam-dump experiments. The run would be completely parasitic without affecting the normal operations and the physics program of the Hall. The most striking signal that this experiment would look for consists of events with ∼ GeV electromagnetic energy deposition. With the detector and the experimental set-up we are proposing, this signal will be easily detected over a negligible background. This striking signature can arise in two classes of models: in those where DM scatters elastically off atomic electrons in the detector, an...

Testing GeV-scale dark matter with fixed-target missing momentum experiments

“…Recently, new beam-dump experiments have aimed to produce light DM candidates and then observe their scattering in downstream detectors [24,[31][32][33][34][35][36][37][38][39]. This is a compelling technique to discover light DM, but its reliance on a small re-scattering probability prevents this approach from reaching the milestone sensitivity of Eq.…”

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

“…Results are reported as upper limit on exclusion plot. More excluding plots for different parameter spaces and/or DM scenarios, together with the detail of the analysis, are reported in [11]. The regions above the lines are excluded since the model, with the chosen parameters, predicts a number of counts greater than two times the sigma of the background.…”

“…BDX was proposed to JLab Program Advisory Committee (PAC) on June 2016 [11]. The PAC found the physics case exiting and conditionally approved the proposal, encouraging the collaboration to perform further studies to benchmark beam-related background simulations.…”

“…For example, LSND measurement of meson production and decay [10] can be used to derive the most stringent constraints to date on the parameter space for invisibly-decaying dark mediators that couple to both baryons and leptons [9]. The Beam Dump experiment (BDX) at JeffersonLab [11] aims to produce and detect LDM, assuming valid the above cited theoretical paradigm. Tacking advantage of the high intensity ∼ GeV electron beam available at JLab, BDX has the unique capability of dramatically improve sensitivity to MeV -GeV DM, extending well beyond the reach of existing and proposed experiments, reaching the limit of the un-reducible background due to beamproduced neutrinos.…”

Search for the Dark Photon and the Dark Higgs Boson at Belle

“…Due to the small coupling to SM particles and the low expected mass of the dark photon, the ideal tools to discover the dark photon and the dark Higgs boson are low energy and high-luminosity experiments such as Belle at KEKB, Belle II at SuperKEKB [24], BaBar at PEP-II [29,30], and dedicated fixed target and beam dump experiments, several of which are planned or under construction [31][32][33][34][35][36][37]. This article focuses on the Higgsstrahlung channel, e + e − → A h .…”