Direct detection of dark matter axions with directional sensitivity

TL;DR

This paper explores how the orientation of long, thin resonant cavities in axion haloscope detectors can produce a detectable modulation in the axion signal, enabling directional detection and insights into galactic dark matter distribution.

Contribution

It introduces a method to utilize cavity orientation for directional sensitivity in axion detection, especially for geometries where the axion wavelength is comparable to cavity size.

Findings

Signal modulation depends on cavity orientation relative to axion momentum distribution.

Directional detection can confirm extraterrestrial origin of axion signals.

Modulation shape provides information about galactic halo models.

Abstract

We study the directional effect of the expected axion dark matter signal in a resonant cavity of an axion haloscope detector, for cavity geometries not satisfying the condition that the axion de Broglie wavelength $\lambda_a$ is sufficiently larger than the cavity dimensions $L$ for a fully coherent conversion, i.e. $\lambda_a \gtrsim 2\pi L$. We focus on long thin cavities immersed in dipole magnets and find, for appropriately chosen cavity lengths, an O(1) modulation of the signal with the cavity orientation with respect the momentum distribution of the relic axion background predicted by the isothermal sphere model for the galactic dark matter halo. This effect can be exploited to design directional axion dark matter detectors, providing an unmistakable signature of the extraterrestrial origin of a possible positive detection. Moreover, the precise shape of the modulation may give information of the galactic halo distribution and, for specific halo models, give extra sensitivity for higher axion masses.