Extended Maximum Likelihood Halo-independent Analysis of Dark Matter Direct Detection Data

TL;DR

This paper extends a maximum-likelihood halo-independent method for analyzing unbinned dark matter detection data, allowing for broader target and interaction types, and provides a rigorous statistical framework with applications showing compatibility of certain dark matter signals with null results.

Contribution

It introduces a generalized, statistically rigorous halo-independent analysis method applicable to various target compositions and interaction types in dark matter detection.

Findings

CDMS-II-Si signal compatible with other null results for specific interactions

Method applicable to elastic and inelastic scattering with general momentum dependence

Provides a rigorous statistical interpretation of dark matter detection data

Abstract

We extend and correct a recently proposed maximum-likelihood halo-independent method to analyze unbinned direct dark matter detection data. Instead of the recoil energy as independent variable we use the minimum speed a dark matter particle must have to impart a given recoil energy to a nucleus. This has the advantage of allowing us to apply the method to any type of target composition and interaction, e.g. with general momentum and velocity dependence, and with elastic or inelastic scattering. We prove the method and provide a rigorous statistical interpretation of the results. As first applications, we find that for dark matter particles with elastic spin-independent interactions and neutron to proton coupling ratio $f_n/f_p=-0.7$, the WIMP interpretation of the signal observed by CDMS-II-Si is compatible with the constraints imposed by all other experiments with null results. We also find a similar compatibility for exothermic inelastic spin-independent interactions with $f_n/f_p=-0.8$.