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共同利用研究成果発表研究会 ＸＭＡＳＳ実験

共同利用研究成果発表研究会 ＸＭＡＳＳ実験. ２００４年１２月１７日 宮城教育大学 福田　善之 宇宙線研究所神岡宇宙素粒子研究施設、 宇宙線研究所ニュートリノセンター、佐賀大、 新潟大、東海大、岐阜大、早稲田大、横浜国大、 ソウル国大、 INR Kiev 、セジョン大、 カリフォルニア州立大アーバイン校. Introduction to XMASS. Ultra-low background multi-purpose detector X enon MASS ive detector for Solar neutrino (pp/7Be)

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共同利用研究成果発表研究会 ＸＭＡＳＳ実験

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  1. 共同利用研究成果発表研究会ＸＭＡＳＳ実験 ２００４年１２月１７日 宮城教育大学 福田　善之 宇宙線研究所神岡宇宙素粒子研究施設、 宇宙線研究所ニュートリノセンター、佐賀大、 新潟大、東海大、岐阜大、早稲田大、横浜国大、 ソウル国大、INR Kiev、セジョン大、 カリフォルニア州立大アーバイン校 宇宙線研究所共同利用研究成果発表会

  2. Introduction to XMASS • Ultra-low background multi-purpose detector • Xenon MASSive detector for Solar neutrino (pp/7Be) • Xenon neutrino MASS detector (double beta decay) • Xenon detector for Weakly Interacting MASSive Particles (DM) Solar neutrino Dark matter Double beta 宇宙線研究所共同利用研究成果発表会

  3. Large self-shield effect Self shielding effect for low energy signals External g ray from U/Th-chain Single phase liquid Xe 23ton all volume 20cm wall cut 30cm wall cut (10ton FV) Volume for shielding Fiducial volume BG normalized by mass PMTs 0 1MeV 2MeV 3MeV • Large Z makes detectors very compact • Large photon yield (42 photon/keV ~ NaI(Tl)) Liquid Xe is the most promising material. 宇宙線研究所共同利用研究成果発表会

  4. Strategy of the XMASS project ~30cm ~1m ~2.5m ~1 ton detector (FV 100kg) Dark matter search ~20 ton detector (FV 10ton) Solar neutrinos Dark matter search Prototype detector (FV 3kg) R&D Confirmation of feasibilities of the ~1ton detector Good results 宇宙線研究所共同利用研究成果発表会

  5. Liq. Xe (30cm)3=30L =100Kg MgF2 window 3kg FV prototype detector OFHC cubic chamber 54 2-inch low BG PMTs • 30 litter liquid Xenon (~100kg) • Oxygen free copper: (31cm)3 • 54 of low-BG 2-inch PMT • Photo coverage ~16% • MgF2 window • 0.9 p.e. / keV@ Detector center 宇宙線研究所共同利用研究成果発表会

  6. n Polyethylene (15cm) Boric acid (5cm) g Lead (15cm) 1.0m EVOH sheets (30μm) OFHC (5cm) Rn free air (~3mBq/m3) 1.9m Shields for several sources Demonstration of reconstruction, self shielding effect, and low background properties Rn 宇宙線研究所共同利用研究成果発表会

  7. + + + B A C Source run (g ray injection from collimators) I Collimator B Collimator C Collimator A DATA MC Well Reproduced Aug. 04 run 宇宙線研究所共同利用研究成果発表会

  8. Source run (g ray injection from collimators) II Aug. 04 run 60Co: 1.17&1.33MeV DATA MC 137Cs: 662keV DATA MC 10-1 10-1 No energy cut, only saturation cut. BG subtracted r=2.884g/cc Arbitrary Unit 10-2 10-2 ~1/10 10-3 10-3 ~1/200 PMT Saturation region 10-4 10-4 10-5 10-5 -15 Reconstructed Z +15cm -15 Reconstructed Z +15cm • Impressive agreements. • Self shield works as expected. • Photo electron yield ~ 0.8p.e./keV for all volume Gamma rays Z= -15 Z= +15 宇宙線研究所共同利用研究成果発表会

  9. Source run (g ray injection from collimators) III Performance of the energy scale stability Collimated g ray source run from center hole 60Co, 1132keV 60Co calibration data Peak position from simple gaussian fit +-0.5% Relative difference (%) Aug. 04 run • No degrading of the energy scale • Stable within +-0.5% Elapsed day 宇宙線研究所共同利用研究成果発表会

  10. External background source Background level was estimated from known sources • g rays from outside shield • PMTs origin • 238U series • 40K • 232Th series • 210Pb in the lead shield MC estimation for full volume [count/keV/day/kg] (=dru) These values are based on the measurements by HPGe. Energy (keV) 宇宙線研究所共同利用研究成果発表会

  11. All volume All volume 20cm FV 20cm FV 10cm FV (3kg) 10cm FV (3kg) Background data Miss-reconstruction due to dead-angle region from PMTs. MC simulation REAL DATA 3.9days livetime Event rate (/kg/day/keV) 10-2/kg/day/keV • MC uses U/Th/K activity from PMTs, etc (meas. by HPGe). • Good agreement (< factor 2) • Self shield effect can be seen clearly. • Very low background (10-2 /kg/day/keV@100 keV) 宇宙線研究所共同利用研究成果発表会

  12. ? Miss reconstruction: dead angle from the PMTs • Scintillation light at the dead angle from PMTs give quite uniform 1p.e. level signal for PMTs. • This cause miss reconst-ruction as if the vertex is around the center of the detector. • Immersing PMTs into LXe and using spherical design solve this problem.  It will give low BG in the ROI for DM search HIT HIT HIT HIT HIT Inside the chamber is just copper surface 宇宙線研究所共同利用研究成果発表会

  13. Internal background source Goal for 1ton detector 1x10-14 g/g 2x10-14 g/g 1ppt • Current results We observe the Bi-Po decay chain. • 238U: = (33±7)x10-14g/g • 232Th: < 23x10-14g/g • Kr: = 3.3±1.1 ppt Factor ~30, but may decay out further (In this time, there is no candidate events) Factor <~10 (under further study) Almost achieved by the distillation process 宇宙線研究所共同利用研究成果発表会

  14. 222Rn decay out Aug.04 run preliminary 238U DT < 1ms 222Rn (1.8days) 3.5MeV 214Bi214Po210Pb b (Emax=3.3MeV) a (7.7MeV) 67ev t1/2 =164msec • 2 separate runs to check 222Rn decay (t1/2=3.8day) • 4th Aug. 0.8day 238U=(72+-11)x10-14 g/g • 10th Aug. 1.0day 238U=(33+-7)x10-14 g/g • Consistent with expected 222Rn decay ((30+-5)x10-14 ) DT: t1/2 = 141+-51msec DL 宇宙線研究所共同利用研究成果発表会

  15. Distillation to reduce Kr (1/1000 by 1 pass) • Very effective to reduce internal impurities (85Kr, etc.) • Processed our Xe before the measurement. Lower temp. Original Xe: ~3 ppb Kr Off gas Xe: 330±100 ppb Kr (measured) ~1% ~3m Operation: 2 atm Processing speed: 0.6 kg / hour Design factor: 1/1000 Kr / 1 pass 13 stage of 2cmf Purified Xe: 3.3±1.1ppt Kr (measured after Kr-enrichment) Higher temp. ~99% 宇宙線研究所共同利用研究成果発表会

  16. Possible DM search • Due to the dead angle from PMTs, it is hard to analyze E<100keV, 10cm FV data. • However, if we exclude such “wall effect” by putting some “light guide,” we can remove low energy mis-reconstruction effect. ~10-2/keV/kg/d, Eth~10keV, and ~3kg FV will be available. • This make possible to search for DM (sensitivity depends on its Eth, if Eth~10keV, ~0.6events/day can be expected if 10-5pb (SI), 100GeV DM  background ~0.6events/day for 20keV signal window) 宇宙線研究所共同利用研究成果発表会

  17. Current status of LG mounting 宇宙線研究所共同利用研究成果発表会

  18. Achieved 1 ton (100kg FV) detector for DM Search • Solve the miss reconst. prob.  immerse PMTs into LXe • Ext. g BG: from PMT’s  Self-shield effect demonstrated • Int. BG: Kr (distillation), Radon  Almost achieved • Neutron: water or LS active shield (1/104) To be studied “Full” photo-sensitive,“Spherical” geometry detector external g ray (60cm, 346kg) external g ray: (40cm, 100kg ) 8x10-5/keV/kg/d /kg/day/keV 80cm dia. Dark matter (10-6 pb, 50GeV, 100 GeV) Q.F. = 0.2 assumed 7Be pp ~800-2” PMTs (1/10 Low BG) 70% photo-coverage ~5p.e./keVee 0 100 200 Energy(keVee) 宇宙線研究所共同利用研究成果発表会

  19. Expected sensitivity 10-4 106 SD 104 Edelweiss Al2O3 10-6 Tokyo LiF 102 Modane NaI Cross section to nucleon [pb] CRESST 1 UKDMC NaI 10-8 XMASS(Ann. Mod.) NAIAD 10-2 XMASS(Sepc.) SI 10-10 10-4 • Large improvements will be expected. • SI ~ 10-45cm2 = 10-9pb • SD~ 10-39cm2= 10-3pb Plots except for XMASS: http://dmtools.berkeley.edu Gaitskell & Mandic 宇宙線研究所共同利用研究成果発表会

  20. Summary • XMASS: DM search with 100kg FV LXe • R&D by 3kg FV prototype is well going Demonstration of reconstruction, self shield, and low BG properties • Ext g rays: 10-2 /kg/day/keV  further self shield Kr: 3.3±1.1ppt requirement almost achieved. Radon (U) (33±7)10-14g/g (Th) < 23 10-14g/g  O(1/30) reduction is enough for 1ton det. • Further study for neutron is needed. • Within a few years, we are planning to build the 100kg FV detector and start to search for DM! 宇宙線研究所共同利用研究成果発表会

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