Background Rejection in the DMTPC Dark Matter Search Using Charge Signals

TL;DR

This paper demonstrates that combining charge readout with optical CCD detection in the DMTPC dark matter detector significantly improves background rejection and sets a stringent upper limit on electron recoil contamination.

Contribution

It introduces a charge readout analysis method that enhances background rejection in the DMTPC dark matter search, achieving a 90% confidence level upper limit on electron rejection.

Findings

Achieved a 90% C.L. upper limit on electron rejection factor of 5.6×10⁻⁶.

Coincidence requirement between charge signals and CCD light reduces backgrounds by over two orders of magnitude.

Demonstrated the effectiveness of combined charge and optical readout in dark matter detection.

Abstract

The Dark Matter Time Projection Chamber (DMTPC) collaboration is developing low-pressure gas TPC detectors for measuring WIMP-nucleon interactions. Optical readout with CCD cameras allows for the detection for the daily modulation in the direction of the dark matter wind, while several charge readout channels allow for the measurement of additional recoil properties. In this article, we show that the addition of the charge readout analysis to the CCD allows us too obtain a statistics-limited 90% C.L. upper limit on the $e^-$ rejection factor of $5.6\times10^{-6}$ for recoils with energies between 40 and 200 keV$_{\mathrm{ee}}$. In addition, requiring coincidence between charge signals and light in the CCD reduces CCD-specific backgrounds by more than two orders of magnitude.