Background Rejection in the DMTPC Dark Matter Search Using Charge Signals

Abstract

The Dark Matter Time Projection Chamber (DMTPC) collaboration is developing a low pressure gas TPC for detecting Weakly Interacting Massive Particle (WIMP)-nucleon interactions. Optical readout with CCD cameras allows for the detection of the daily modulation of the direction of the dark matter wind. In order to reach sensitivities required for WIMP detection, the detector needs to minimize backgrounds from electron recoils. This paper demonstrates that a simplified CCD analysis achieves $7.3\times 10^{-5}$ rejection of electron recoils while a charge analysis yields an electron rejection factor of $3.3\times 10^{-4}$ for events with ${}^{241}$Am-equivalent ionization energy loss between 40 keV and 200 keV. A combined charge and CCD analysis yields a background-limited upper limit of $1.1\times 10^{-5}$ (90% confidence level) for the rejection of $\gamma$ and electron events. Backgrounds from alpha decays from the field cage are eliminated by introducing a veto electrode that surrounds the sensitive region in the TPC. CCD-specific backgrounds are reduced more than two orders of magnitude when requiring a coincidence with the charge readout.

18 pages, 12 figures. Preprint accepted by NIM A

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Cited by in corpus (9)

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• Complementarity of dark matter detectors in light of the neutrino background
• Readout technologies for directional WIMP Dark Matter detection
• Measurement of the directional sensitivity of DMTPC detectors
• WIMP detection and slow ion dynamics in carbon nanotube arrays
• Low energy electron/recoil discrimination for directional Dark Matter detection
• In situ measurement of the electron drift velocity for upcoming directional Dark Matter detectors
• Overview of Non-Liquid Noble Direct Detection Dark Matter Experiments
• Observables for Recoil Identification in High-Definition Gas Time Projection Chambers