12:00–1:00 pm ERC 401
Dylan J Temples (Northwestern Universtiy / Fermilab)
"Understanding neutrino background implications in LXe-TPC dark matter searches using 127Xe electron captures"
Host: Daniel Baxter
Dark matter searches using dual-phase xenon time projection chambers (LXe-TPC) rely on the discrimination between electronic recoils (background) and nuclear recoils (signal) based on the ratio of ionization electrons to scintillation photons produced by the interaction in the liquid xenon. This discrimination is calibrated at low energies using tritium β-decays. However, neutrino and Compton scatters from inner-shell electrons of xenon atoms result in the emission of Auger electrons and x-rays in addition to the primary recoiling electron, and thus have a different event topology than β-decays and valence-shell electron recoils. Due to their low kinetic energy and large numbers, these secondary particles can deposit larger amounts of energy within a small radius, which is uncharacteristic of valence electron recoils and is more akin to nuclear recoils. This affects the profile of the neutrino-electron scattering background in a way that is, so far, uncalibrated and unaccounted for in LXe-TPC dark matter searches, and presents the possibility of a false discovery claim. To investigate the significance of this effect, electrons capture decays of 127Xe are used to simulate the vacancies produced by inner-shell e−ν scatters in the Xenon Electron-recoil L-shell Discrimination Analyzer (XELDA) detector. The 127Xe source produces a high-purity sample of inner-shell vacancies accompanied by an Auger cascade that can easily be isolated from the prompt γ’s emitted in the decay. In this talk, I will present preliminary results from a cross-calibration of the XELDA detector using both 127Xe EC-decays and 3H β-decays. The observed discrepancy reduces the efficiency with which neutrino-induced electron recoils can be rejected in large-scale LXe-TPC dark matter searches, such as LUX-ZEPLIN and DARWIN.