First underground results with NEWAGE-0.3a direction-sensitive dark matter detector

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$20\times 25\times 31{\text{cm}}^3$ and 0.0115 kg, respectively. With an exposure of 0.524 kg days, 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$/c^2$ WIMPs. We studied the remaining background and found that ambient γ-rays contributed about one-fifth of the remaining background and radioactive contaminants inside the gas chamber contributed the rest.