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

References in corpus (9)

• First results from DAMA/LIBRA and the combined results with DAMA/NaI
• Results from a Low-Energy Analysis of the CDMS II Germanium Data
• Improved Spin-Dependent WIMP Limits from a Bubble Chamber
• First Dark Matter Search Results from a Surface Run of the 10-L DMTPC Directional Dark Matter Detector
• Optimizing WIMP directional detectors
• Markov Chain Monte Carlo analysis to constrain Dark Matter properties with directional detection
• First Results from the DRIFT-IIa Dark Matter Detector
• Exclusion limits from data of directional Dark Matter detectors
• Charge amplification concepts for direction-sensitive dark matter detectors