Spin-dependent dark matter interactions at loop-level in Ar and Xe

TL;DR

This paper compares the detection capabilities of xenon and argon in dark matter experiments, highlighting the significance of loop-level contributions in pseudoscalar-mediated interactions, especially for argon with zero nuclear spin.

Contribution

It demonstrates that loop-level effects induce detectable spin-independent interactions in argon, which are negligible at tree-level, thus impacting dark matter detection strategies.

Findings

Loop-level contributions enable argon to detect pseudoscalar interactions.

Loop effects are significant for xenon at low recoil energies.

Detection sensitivity is affected by loop-level interactions in both gases.

Abstract

Xenon and argon are the two noble gases used in tonne scale dark matter direct detection experiments. We compare the detection capability of both target elements for interactions due to a pseudoscalar mediator including loop-level contributions to the cross section. At tree-level this type of interaction depends on the nuclear spin and would thus not be detectable in argon-based detectors, since Ar has spin zero. However, at the loop-level the same interaction yields spin-independent contributions that would be detectable in an argon target and are not negligible with respect to the tree-level interactions in xenon, because these are momentum suppressed. In fact, the loop-level contributions are also important for xenon-based experiments at low recoil energies, which could change their discovery reach for this interaction.