MiniCLEAN Dark Matter Experiment

Abstract

The MiniCLEAN dark matter experiment will exploit a single-phase liquid-argon detector instrumented with 92 photomultiplier tubes placed in the cryogen temperature with 4-$\pi$ coverage of a 500 kg (150 kg) target (fiducial) mass. The detector design strategy emphasizes scalability to target masses of order 10 tons or more. The detector is designed also for a liquid neon target that allows for an independent verification of signal and background and a test of the expected dependence of the WIMP-nucleus interaction rate. For MiniCLEAN, PMT stability and calibration are essential. The \textit{In-situ} optical calibration will be able monitor the PMT stability and maintain the calibration. In MiniCLEAN, we use a Light-Emitting Diode(LED)- based light injection system to provide single photons for calibration, the calibration can be performed in near real-time, providing a continuous monitor at the condition of the detector. The intrinsic $^{39}$Ar beta emitter provides another way to calibrate the detector thanks to well defined properties and uniformly distributed inside the detector volume. The energy scale can be determined by fitting the energy spectrum of experimental $^{39}$Ar data. Moreover, the preliminary results from cold gas run shows the best measurement on triplet lifetime ($\sim$ 3.5 $\mu$ s). The results confirms the high purity of argon is attained by MiniCLEAN's purification system. The long triplet lifetime in gaseous argon can be exploit to obtain better performance of pulse shape discrimination (PSD) for future dark matter detector, also the low density of gaseous argon reduced the multi-scattering neutron backgrounds. On the other hand, by injecting $^{39}$Ar spike, the electronic recoil events due to $^{39}$Ar beta decay can be used to test the limit of PSD in liquid argon. The results will be informative for future multi-tonne LAr detector.