Optimizing WIMP directional detectors

Abstract

We study the dependence of the exposure required to directly detect a WIMP directional recoil signal on the capabilities of a directional detector. Specifically we consider variations in the nuclear recoil energy threshold, the background rate, whether the detector measures the recoil momentum vector in 2 or 3 dimensions and whether or not the sense of the momentum vector can be determined. We find that the property with the biggest effect on the required exposure is the measurement of the momentum vector sense. If the detector cannot determine the recoil sense, the exposure required is increased by an order of magnitude for 3-d read-out and two orders of magnitude for 2-d read-out. For 2-d read-out the required exposure, in particular if the senses can not be measured, can be significantly reduced by analyzing the reduced angles with the, time dependent, projected direction of solar motion subtracted. The background rate effectively places a lower limit on the WIMP cross-section to which the detector is sensitive; it will be very difficult to detect WIMPs with a signal rate more than an order of magnitude below the background rate. Lowering the energy threshold also reduces the required exposure, but only for thresholds above 20 keV.

WIMP event rates in directional experiments: The diurnal variation signature

“…Better signatures are expected in directional experiments in which one measures not only the recoil energy but the direction of the nuclear recoil as well. Some of the requirements that should be met by such detectors have recently been discussed [50,66]. To fully exploit the advantages of such detectors one should be able to distinguish between recoils with momenta p and −p (sense of direction), which now appears to be feasible.…”

“…experiments in which the direction of the recoiling nucleus is observed [40,[45][46][47][48][49][50][51][52][53][54][55]. The theoretical analysis of these papers is very useful to experiments and, in particular, the statistical analysis given by Morgan and Green [49].…”

“…We will see that, to fully exploit the advantages offered by the directional experiments, the detectors should be able to distinguish the head from the tail of the track, i.e. the sense of direction of motion [66] (an analysis of the requirements imposed on the directional detectors, focusing especially on energy threshold effects and minimization of background, has recently appeared [50]). We find that some of the advantages of the diurnal variation will persist, even if the sense of direction cannot be determined.…”

Magnetic inelastic dark matter: Directional signals without a directional detector

“…The average nuclear recoil angle with respect to the Earth's motion, cos γ , is a robust model-independent statistic for directional detection [47,58,59]. Here we use cos γ * , the WIMP recoil angle with respect to the Earth's motion.…”

Earth’s stopping effect in directional dark matter detectors

“…The recoil energy spectrum of DM scattering off nuclei in directional detectors has been studied extensively first in [11] and later in [12][13][14][15][16][17][18][19][20][21][22]. 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.…”