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6 発表済み論文 K. Abe et al. / Physics Letters B 79 (23) Light WIMP search Physics Letters B 79 (23) Data DAMA/LIBRA等で示唆される軽い暗黒物質探索 8GeV signal MC XMASSで観測したevent rateを上回る領域を排除 select these events a time-of-flight correction is made to the tim- 2GeV 7GeV Fig. 6. WIMP signal acceptance eﬃciency after data reduction for the analysis Results discussion and 2 4 Fig. 7. Simulated WIMP energy spectra in the XMASS detector assuming the maximum cross section that provides a signal rate no larger than the observation in any bin above.3 kevee. gaee event rate (kg-day-kev-) ing distribution of each event assuming the event vertex is on the surface of the PMT closest to the charge-weighted center of gravity of the event. After this correction the timing distribution of Cherenkov-like events is found to be narrower than that for scintillation-like events. Events with more than 6% of their PMT hits occurring within the first 2 ns of the event window are re moved as Cherenkov-like. The ratio of the number of PMT hits 4 4 within 2 ns relative to3.5 the total number 5keVof hits in the 3.5 the first kev event3window for all events (head-to-total ratio) is shown in Fig Each shown in Fig step of the data reduction is2.5 2 expected WIMP acceptance 2 eﬃciency of these cuts was The.5.5 estimated with the detector simulation. In the simulation WIMP recoil energy spectra were generated for each WIMP mass and MC.5.5 events the detector volume were distributed uniformly throughout 2.5 scintillation decay 2 using a liquid constant of 25 ns 4 [6]. Fig. 6 shows the resulting signal acceptance eﬃciency at energies below kevee. The size of the error bars comes primarily from the systematic uncertainty in the xenon 4 4 scintillation decay constant, 25 ± is estimated based difference between the 3.5 ns, whichkev 3.5 on the5kev 3 model [6] and the NEST model 3 XMASS [7] based on [8]. A sys2.5 error on the selection eﬃciency 2.5 tematic is determined based on 2 the error resulting from a linear fit2 to the points in the figure. At.5.5 the.3 kevee analysis threshold this error is 6.%. data MC scaled energy (kev) Solar axion search o-ps -5 reactors -6 beam dump Physics Letters B 724 (23) Tm -8 太陽中でelectronからaxionが制動輻射されたり Compton散乱によってaxionが放出される可能性 -9 Si(Li) - Ge XMASS - solar neutrino DFSZ -2 Red Giants KSVZ -3 Fig. 7 shows simulated WIMPs energy spectra overlaid on the observed spectrum after the data reduction was applied. WIMPs are assumed to be distributed in an isothermal halo withthv o = 22 km/s, a galactic escape velocity of v esc = 65 km/s, and an Dec mass (ev) 7 実験的探索としては世界最高感度を達成 Fig. 8. Spin-independent elastic WIMP-nucleon cross section as a function of WIMP mass. All systematic uncertainties except that from Leff are taken into account in the XMASS 9% C.L. limit line. The effect of the Leff uncertainty on the limit is shown in the band. Limits from other experiments and favored regions are also shown [4 9]. 23 ICRR Annual meeting Keishi Hosokawa 6

7 WIMP%Xe29 Xe29 Nuclearrecoil WIMP WIMP Xe29 Nuclearrecoil τ=.97ns 4keVgamma

8 v

10 PMT

11 PMT PMT

13 RFB 検出器再構成まとめ 23年3月 5月 23年7月 3日 23年7月 8日銅リング装着!! PMT窓側面に高純度Alを蒸着硝酸を用いた PMT窓洗浄 23年7月9 日 23年7月 3日電解研磨後 PMT holder 組み立て 23年8月2 27日 PMT 装填ケーブリング 23年月 XMASS Refurbishmentは事故なく完了 Dec. 2th 23 ICRR Annual meeting Keishi Hosokawa 3

14 RFB前後の検出器表面 RFB後 RFB前 Dec. 2th 23 ICRR Annual meeting Keishi Hosokawa 4

18 maxpe/totalpe totpe npe maxpe/totalpe totpe npe xpe/totalpe xpe/totalpe

19 maxpe/totalpe npe maxpe/totalpe npe 8 xpe/totalpe xpe/totalpe

DAMA/LIBRA領域をカバーしている実験が見込まれて季節変動を用いた実験では最も良い感度を持つことが期待されるは現状なく XMASSなら短期間で同等の統計量を得る事が可能これから 3sigma 低エネルギー閾値で年以上の安定した This

21 Seasonal modulation XMASSコミッショニングランの結果と展望暗黒物質事象数の季節変動の解析を用いてコミッショニング季節変動の解析を用いてコミッショニングランでもDAMA/LIBRAと同程度の感度がとを示すことができたランでもDAMA/LIBRAと同程度の感度 PhaseI XMASS 8kgでは改造を進めており今秋から長期ラン(>年を目指してい今後統計を増やすだけでなく低いエネルギーにおいて/以上のバックグラウンド季節変動を用いて DAMA/LIBRA領域をカバーしている実験が見込まれて季節変動を用いた実験では最も良い感度を持つことが期待されるは現状なく XMASSなら短期間で同等の統計量を得る事が可能これから 3sigma 低エネルギー閾値で年以上の安定した This work, 9%CL データ取得を行う / BG, Eth=.3keVee, modulation year Masaki Yamashita, Univ o 23A JPSICRR, 山下 Dec. 2th 23 ICRR Annual meeting Keishi Hosokawa 2

24 まとめコミッショニングデータを用いて物理成果を発表している XMASS検出器改修(Refurbishment) が完了し運転を再開した - 簡単なstudyで目論み通りのBG レベルを確認 - 当初の目標感度にせまる事を期待 RFB後のXMASSでの観測と並行して XMASS-.5のデザインも進めていく Dec. 2th 23 ICRR Annual meeting Keishi Hosokawa 24

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