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Register a new userDark Matter Directionality Revisited with a High Pressure Xenon Gas Detector
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An observation of the anisotropy of dark matter interactions in a direction-sensitive detector would provide decisive evidence for the discovery of galactic dark matter. Directional information would also provide a crucial input to understanding its distribution in the local Universe. Most of the existing directional dark matter detectors utilize particle tracking methods in a low-pressure gas time projection chamber. These low pressure detectors require excessively large volumes in order to be competitive in the search for physics beyond the current limit. In order to avoid these volume limitations, we consider a novel proposal, which exploits a columnar recombination effect in a high-pressure gas time projection chamber. The ratio of scintillation to ionization signals observed in the detector carries the angular information of the particle interactions. In this paper, we investigate the sensitivity of a future directional detector focused on the proposed high-pressure Xenon gas time projection chamber. We study the prospect of detecting an anisotropy in the dark matter velocity distribution. We find that tens of events are needed to exclude an isotropic distribution of dark matter interactions at 95% confidence level in the most optimistic case with head-to-tail information. However, one needs at least 10-20 times more events without head-to-tail information for light dark matter below 50 GeV. For an intermediate mass range, we find it challenging to observe an anisotropy of the dark matter distribution. Our results also show that the directional information significantly improves precision measurements of dark matter mass and the elastic scattering cross section for a heavy dark matter.
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Nuclear emulsion is a well-known detector type proposed also for the directional detection of dark matter. In this paper, we study one of the most important properties of direction-sensitive detectors: the preservation by nuclear recoils of the direction of impinging dark matter particles. For nuclear emulsion detectors, it is the first detailed study where a realistic nuclear recoil energy distribution with all possible recoil atom types is exploited. Moreover, for the first time we study the granularity effect on the emulsion detector directional performance. As well as we compare nuclear emulsion with other directional detectors: in terms of direction preservation nuclear emulsion outperforms the other detectors for WIMP masses above 100 GeV/c$^2$.
We extend the study of the performance of a prototype two-phase liquid xenon WIMP dark matter detector to recoil energies below 20 keV. We demonstrate a new method for obtaining the best estimate of the energies of events using a calibrated sum of charge and light signals and introduce the corresponding discrimination parameter, giving its mean value at 4 kV/cm for electron and nuclear recoils up to 300 and 100 keV, respectively. We show that fluctuations in recombination limit discrimination for most energies, and reveal an improvement in discrimination below 20 keV due to a surprising increase in ionization yield for low energy electron recoils. This improvement is crucial for a high-sensitivity dark matter search.
NEWAGE is a direction-sensitive dark matter search using a low-pressure gaseous time projection chamber. A low alpha-ray emission rate micro pixel chamber had been developed in order to reduce background for dark matter search. We conducted the dark matter search at the Kamioka Observatory in 2018. The total live time was 107.6 days corresponding to an exposure of 1.1 kg${cdot}$days. Two events remained in the energy region of 50-60 keV which was consistent with 2.5 events of the expected background. A directional analysis was carried out and no significant forward-backward asymmetry derived from the WIMP-nucleus elastic scatterings was found. Thus a 90% confidence level upper limit on Spin-Dependent WIMP-proton cross section of 50 pb for a WIMP mass of 100 GeV/c2 was derived. This limit is the most stringent yet obtained from direction-sensitive dark matter search experiments.
The angular dependence of the columnar recombination in xenon gas, if observed for low energy nuclear tracks, can be used for a direction-sensitive dark matter search. We measured both scintillation and ionization to study columnar recombination for 5.4 MeV alpha particles in a high pressure gas detector filled with 8 atm xenon. Since the recombination photons are emitted several~$mu$s after de-excitation emission, scintillation photons are separated to the fast and slow components. The fast component does not show dependence on the track angle relative to the drift electric field, on the other hand, the slow component increases when the track is aligned with the electric field. The result indicates that the track angle relative to the electric field can be reconstructed from the scintillation time profile.
The first directional dark matter search with three-dimensional tracking with head-tail sensitivity (3d-vector tracking analysis) was performed with a gaseous three-dimensional tarcking detector, or the NEWAGE-0.3b detector. The search was carried out from July 2013 to August 2017 (Run14 to Run18) at the Kamioka underground laboratory. The total livetime is 434.85 days corresponding to an exposure of 4.51 kg$cdot$days. A 90 % confidence level upper limit on spin-dependent WIMP-proton cross section of $4.3 times10^{2}$ pb for WIMPs with the mass of 150 GeV/$c^2$ is obtained.
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