Fog on the horizon: a new definition of the neutrino floor for direct dark matter searches

TL;DR

This paper redefines the neutrino floor in dark matter detection as the boundary of the neutrino fog, providing a new calculation method that minimizes arbitrary assumptions and highlights the impact of systematic uncertainties.

Contribution

It introduces a new, assumption-free definition of the neutrino floor based on the derivative of discovery limits, emphasizing systematic uncertainties in neutrino fluxes.

Findings

Neutrino floor differs significantly in the sub-GeV and above 20 GeV ranges.

The new method reduces dependence on experimental parameters like exposure and energy threshold.

Results are broadly similar to previous estimates but show notable deviations in specific energy ranges.

Abstract

The neutrino floor is a theoretical lower limit on WIMP-like dark matter models that are discoverable in direct detection experiments. It is commonly interpreted as the point at which dark matter signals become hidden underneath a remarkably similar-looking background from neutrinos. However, it has been known for some time that the neutrino floor is not a hard limit, but can be pushed past with sufficient statistics. As a consequence, some have recently advocated for calling it the "neutrino fog" instead. The downside of current methods of deriving the neutrino floor are that they rely on arbitrary choices of experimental exposure and energy threshold. Here we propose to define the neutrino floor as the boundary of the neutrino fog, and develop a calculation free from these assumptions. The technique is based on the derivative of a hypothetical experimental discovery limit as a function of exposure, and leads to a neutrino floor that is only influenced by the systematic uncertainties on the neutrino flux normalisations. Our floor is broadly similar to those found in the literature, but differs by almost an order of magnitude in the sub-GeV range, and above 20~GeV.