Daily modulation as a smoking gun of dark matter with significant stopping rate

Abstract

We point out that for a range of parameters, the flux of DM may be stopped significantly by its interactions with the Earth. This can significantly degrade the sensitivity of direct detection experiments to DM candidates with large interactions with terrestrial nuclei. We find that a significant region of parameter space remains unconstrained for DM ≲ a few GeV. For DM candidates with moderate levels of stopping power, the flux of DM may be blocked from below but not above a detector, thereby producing a novel daily modulation. This can be explored by low threshold detectors placed on the surface or in shallow sites in the south hemisphere. A. InsulatorsDifferent experiments lie on different sites with different ground compositions. However by considering for example the site of the LUX experiment which is located at the Homestake mine, chemical element composition analysis [10] suggests the significant existence of insulating chemical compounds such as SiO 2 , Al 2 O 3 , FeO, etc. Scattering of WIMPs with electrons from these chemical compounds can * shoemaker@cp3-origins.net † kouvaris@cp3.dias.sdu.dk PHYSICAL REVIEW D 90, 095011 (2014) 1550-7998=2014=90(9)=095011(11) 095011-1

Earth’s stopping effect in directional dark matter detectors

“…They can lose energy either by interactions with nuclei, or if allowed, by interactions with electrons. The latter can be either in the form of DM interactions with electrons in metallic layers of the earth, or in the form of DM-electron interactions that result in atomic excitations [25]. The determination of the most effective mode of decelerating DM particles depends strongly on the type of DM-nucleus interactions as well as the precise geological composition of the earth.…”

“…In this case, since there is no way to know the direction of the recoiled nucleus, the effect can be seen indirectly via the observation of a diurnal modulated signal. As it was demonstrated in [25], since the earth moves with a nonzero velocity with respect to the rest frame of the galaxy, a daily varying DM signal is created because as the earth rotates around its own axis, the DM particles coming from the direction of the DM wind travel different distances underground at different times during a sidereal day. The observation of such a diurnal modulated signal can reveal information about the nature of DM-nucleon interactions.…”

“…Let us consider in some detail the different directions and angles involved in the problem. Following [25] we define θ l to be the latitude of the detector, and we choose the z-axis with direction south-north pole. α is the angle between v e and the z-axis.…”

“…DM particles can arrive at the detector from different angles, having traveled different distances underground. Although DM particles are expected to interact feebly with nucleons, as it was pointed out in [25], there is DM parameter space especially for light DM candidates where DM-nuclei interactions as the particle travels underground might have an observable effect on the recoil energy spectrum of the detectors. There are two ways that underground DMnuclei interactions can affect the spectrum.…”

“…for contact interactions σ ∼ 1/v 2 ). The study of this stopping effect of the earth was studied in the context of conventional non-directional detectors in [25,26]. In this case, since there is no way to know the direction of the recoiled nucleus, the effect can be seen indirectly via the observation of a diurnal modulated signal.…”