New directional signatures from the nonrelativistic effective field theory of dark matter

Abstract

The framework of non-relativistic effective field theory (NREFT) aims to generalise the standard analysis of direct detection experiments in terms of spin-dependent (SD) and spin-independent (SI) interactions. We show that a number of NREFT operators lead to distinctive new directional signatures, such as prominent ring-like features in the directional recoil rate, even for relatively low mass WIMPs. We discuss these signatures and how they could affect the interpretation of future results from directional detectors. We demonstrate that considering a range of possible operators introduces a factor of 2 uncertainty in the number of events required to confirm the median recoil direction of the signal. Furthermore, using directional detection, it is possible to distinguish the more general NREFT interactions from the standard SI/SD interactions at the 2σ level with O(100 − 500) events. In particular, we demonstrate that for certain NREFT operators, directional sensitivity provides the only method of distinguishing them from these standard operators, highlighting the importance of directional detectors in probing the particle physics of dark matter.

A review of the discovery reach of directional Dark Matter detection

“…We note that an enhanced ring-like feature may appear for certain non-relativistic operators [165,166] described in Sec. III F. For operators coupling to v ⊥ , the recoil spectrum is governed by the transverse Radon Transform f T (v min ,r) (Eq.…”

“…Ref. [165] compared the directionality of the signal for a number of NR operators, assuming equal numbers of events for each operator. The resulting signals may be more strongly directional (for operators coupling to q) or more isotropic (for operators coupling to v ⊥ ) than in the standard SI/SD scenario.…”

“…This suppression leads to an enhanced ring, which is observable for larger values of v min , up to v min ≈ 2v lab . For these NR operators, then, a ring-like feature may be visible for WIMP masses as low as 20 − 30 GeV or for energy thresholds up to E th ∼ 20 keV for heavier WIMPs [165].…”

“…Using the framework of non-relativistic (NR) effective theory, Ref. [165] concludes that there may be roughly a factor of 2 uncertainty on the number of events required, owing to a lack of knowledge about which operator mediates the interaction.…”

Earth’s stopping effect in directional dark matter detectors

“…In all the above papers, the energy recoil spectrum has been studied for the two generic cases of spin-independent and spin-dependent DM-nucleon contact interactions. An extension to more generic non-relativistic scattering operators was studied in [23,24].…”