LUX-ZEPLIN

Abstract:

These proceedings address a recent publication by the ANITA collaboration of four upward-pointing cosmic-ray-like events observed in the first flight of ANITA. Three of these events were consistent with stratospheric cosmic-ray air showers where the axis of propagation does not intersect the surface of the Earth. The fourth event was consistent with a primary particle that emerges from the surface of the ice suggesting a possible τ-lepton decay as the origin of this event. These proceedings follow-up on the modeling and testing of the hypothesis that this event was of τ neutrino origin.

Abstract:

We report on a dark matter search for a Weakly Interacting Massive Particle (WIMP) in the mass range mx ∈ [4; 30] GeV/c^2 with the EDELWEISS-III experiment. A 2D profile likelihood analysis is performed on data from eight selected detectors with the lowest energy thresholds leading to a combined fiducial exposure of 496 kg-days. External backgrounds from γ-and β-radiation, recoils from 206Pb and neutrons as well as detector intrinsic backgrounds were modelled from data outside the region of interest and constrained in the analysis. The basic data selection and most of the background models are the same as those used in a previously published analysis based on Boosted Decision Trees (BDT) [1]. For the likelihood approach applied in the analysis presented here, a larger signal efficiency and a subtraction of the expected background lead to a higher sensitivity, especially for the lowest WIMP masses probed. No statistically significant signal was found and upper limits on the spin-independent WIMP-nucleon scattering cross section can be set with a hypothesis test based on the profile likelihood test statistics. The 90% C.L. exclusion limit set for WIMPs with mx = 4 GeV=c^2 is 1:6 X 10^-39 cm2, which is an improvement of a factor of seven with respect to the BDT-based analysis. For WIMP masses above 15 GeV/c^2 the exclusion limits found with both analyses are in good agreement.