Calvin Gao with Dan Akerib and Tom Shutt

Analysis of Single-Electron/Few-Electron Background in LUX S2 Data

The LUX dark matter experiment consists of a two-phase xenon detector which detects interactions between particles and the xenon nuclei and electrons. Such interactions will excite the xenon atoms causing them to emit photons and electrons. The initial light signal (S1) from the emitted photon will be detected by PMT arrays mounted to the top and bottom of the vessel. The detector employs an electric field to drift the electrons upwards through the liquid until it reaches the surface, creating a second light signal (S2) as it travels through the gas phase. A low energy Weakly Interacting Massive Particle (WIMP) signal results in a visible S2 signal, but a sub-threshold S1, therefore, the S2 signal is more reliable for analysis. However, owing to a less than ideal extraction field, only around 60% of the drifting electrons leave the liquid phase promptly. The residual electrons tunnel out of the liquid with a longer time constant, resulting in a non-prompt electron background. The exact dynamics of this phenomenon remain uncertain. Analysis of the raw LUX data is necessary in order to determine the single electron/few-electron background, which in turn allows for the possibility of analyzing low-mass WIMP signals. The current software used to analyze the raw data cuts the data into specified groups of pulses in a manner that prevents the electron background from being isolated and studied. To fully understand the electron background and to analyze low mass WIMP events, it’s necessary for us to characterize the background in the raw data directly.