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Register a new userDevelopment of a low-alpha-emitting {mu}-PIC for NEWAGE direction-sensitive dark-matter search
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NEWAGE is a direction-sensitive dark-matter-search experiment that uses a micro-patterned gaseous detector, or {mu}-PIC, as the readout. The main background sources are {alpha}-rays from radioactive contaminants in the {mu}-PIC. We have therefore developed a low-alpha-emitting {mu}-PICs and measured its performances. We measured the surface {alpha}-ray emission rate of the {mu}-PIC in the Kamioka mine using a surface {alpha}-ray counter based on a micro TPC.
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Direction sensitivity could provide robust evidence for the direct detection of weakly interacting massive particles constituting dark matter. However, the sensitivity of this method remains low due to the radioactive backgrounds. The purpose of this study is to develop a low-background detector as a two-dimensional imaging device for a gaseous time projection chamber. In direction-sensitive dark matter experiments~(e.g. NEWAGE), $alpha$-rays emitted from the detector components often create substantial radioactive backgrounds. Based on the study of the background of NEWAGE, a new detector low-$alpha$ $mu$-PIC is developed. The produced $mu$-PIC performs well as a gas detector and the $alpha$-ray emission rate from the $mu$-PIC reduced by a factor of 100.
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 known direction of motion of dark matter particles relative to the Earth may be a key for their unambiguous identification even in the presence of backgrounds. We describe a prototype detector that is able to reconstruct direction vectors of weakly interacting massive particles that may the dominant constituent of the dark matter in our galaxy. The detector uses a low-density gas (CF4) in a 10liter time-projection chamber with mesh-based electrodes and optical and charge readout. Initial results confirm good performance in the reconstruction of direction angle and sense (head-tail) for low-momentum nuclear recoils.
A direction-sensitive dark matter search experiment at Kamioka underground laboratory with the NEWAGE-0.3a detector was performed. The NEWAGE- 0.3a detector is a gaseous micro-time-projection chamber filled with CF4 gas at 152 Torr. The fiducial volume and target mass are 20*25*31 cm3 and 0.0115 kg, respectively. With an exposure of 0.524 kgdays, improved spin-dependent weakly interacting massive particle (WIMP)-proton cross section limits by a direction-sensitive method were achieved including a new record of 5400 pb for 150 GeV/c2 WIMPs. We studied the remaining background and found that ambient gamma-rays contributed about one-fifth of the remaining background and radioactive contaminants inside the gas chamber contributed the rest.
We have carried out the dark matter search with a 116g direction-sensitive stilbene crystal in Kamioka Observatory. With the crystal fixed to the earth, we searched the modulation of thelight output. No modulation signal was found due to the small size of the detector crystal and the higher background rate yet to be eliminated. However, it demonstrated the effectiveness of the method of direction sensitive search for the dark matter with an implementation of the anisotropic organic scintillation crystal.
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