Likelihood Approach to the First Dark Matter Results from XENON100

TL;DR

This paper presents a statistical framework using the Profile Likelihood ratio for analyzing dark matter direct detection experiments, applied to XENON100 data to improve limits on WIMP interactions.

Contribution

It introduces a comprehensive likelihood-based method incorporating systematic uncertainties and control data, enhancing analysis of dark matter search results.

Findings

Stronger upper limits on WIMP-nucleon cross-section.

Method effectively incorporates systematic uncertainties.

Applied successfully to XENON100 data.

Abstract

Many experiments that aim at the direct detection of Dark Matter are able to distinguish a dominant background from the expected feeble signals, based on some measured discrimination parameter. We develop a statistical model for such experiments using the Profile Likelihood ratio as a test statistic in a frequentist approach. We take data from calibrations as control measurements for signal and background, and the method allows the inclusion of data from Monte Carlo simulations. Systematic detector uncertainties, such as uncertainties in the energy scale, as well as astrophysical uncertainties, are included in the model. The statistical model can be used to either set an exclusion limit or to make a discovery claim, and the results are derived with a proper treatment of statistical and systematic uncertainties. We apply the model to the first data release of the XENON100 experiment, which allows to extract additional information from the data, and place stronger limits on the spin-independent elastic WIMP-nucleon scattering cross-section. In particular, we derive a single limit, including all relevant systematic uncertainties, with a minimum of 2.4x10^-44 cm^2 for WIMPs with a mass of 50 GeV/c^2.