Dark matter astrophysical uncertainties and the neutrino floor

TL;DR

This paper investigates how astrophysical uncertainties affect the neutrino background in direct dark matter detection, revealing that these uncertainties can significantly raise the expected background levels and impact WIMP detection prospects.

Contribution

It extends the WIMP+neutrino analysis to include astrophysical uncertainties, showing their impact on the neutrino floor and detection sensitivity, especially for low WIMP masses.

Findings

Astrophysical uncertainties alter the shape of the neutrino floor.

Neutrino backgrounds may dominate at cross sections up to ten times higher than previously estimated.

Uncertainties affect WIMP parameter estimation and discrimination from neutrinos.

Abstract

The search for weakly interacting massive particles (WIMPs) by direct detection faces an encroaching background due to coherent neutrino-nucleus scattering. For a given WIMP mass the cross section at which neutrinos constitute a dominant background is dependent on the uncertainty on the flux of each neutrino source from either the Sun, supernovae or atmospheric cosmic ray collisions. However there are also considerable uncertainties with regard to the astrophysical ingredients to the predicted WIMP signal. Uncertainties in the velocity of the Sun with respect to the Milky Way dark matter halo, the local density of WIMPs, and the shape of the local WIMP speed distribution all have an effect on the expected event rate in direct detection experiments and hence will change the region of the WIMP parameter space for which neutrinos are a significant background. In this work we extend the WIMP+neutrino analysis to account for the uncertainty in the astrophysics dependence of the WIMP signal. We show the effect of uncertainties on projected discovery limits with an emphasis on low WIMP masses (less than 10 GeV) when Solar neutrino backgrounds are most important. We find that accounting for astrophysical uncertainties changes the shape of the neutrino floor as a function of WIMP mass but also causes it to appear at cross sections up to an order of magnitude larger, extremely close to existing experimental limits - indicating that neutrino backgrounds will become an issue sooner than previously thought. We also explore how neutrinos hinder the estimation of WIMP parameters and how astrophysical uncertainties impact the discrimination of WIMPs and neutrinos with the use of their respective time dependencies.