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 2004年12月17日 宇宙線研究所共同利用研究成果発表会 1 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 2004年12月17日 宇宙線研究所共同利用研究成果発表会 2 Self shielding effect for low energy signals Volume for shielding Fiducial volume External g ray from U/Th-chain BG normalized by mass Single phase liquid Xe 23ton all volume 20cm wall cut 30cm wall cut (10ton FV) Large self-shield effect PMTs 0 1MeV Large Z makes detectors very compact Large photon yield (42 photon/keV ~ NaI(Tl)) Liquid Xe is the most promising material. 2004年12月17日 宇宙線研究所共同利用研究成果発表会 2MeV 3MeV 3 Strategy of the XMASS project ~30cm ~1m ~1 ton detector (FV 100kg) Prototype detector Dark matter search (FV 3kg) R&D Confirmation of feasibilities of the ~1ton detector ~2.5m ~20 ton detector (FV 10ton) Solar neutrinos Dark matter search Good results 2004年12月17日 宇宙線研究所共同利用研究成果発表会 4 3kg FV prototype detector OFHC cubic chamber 54 2-inch low BG PMTs Liq. Xe 3 (30cm) =30L =100Kg MgF2 window 2004年12月17日 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 5 Shields for several sources n g 1.0m Rn 1.9m 2004年12月17日 Polyethylene (15cm) Boric acid (5cm) Lead (15cm) EVOH sheets (30μm) OFHC (5cm) Rn free air (~3mBq/m3) 宇宙線研究所共同利用研究成果発表会 6 Source run (g ray injection from collimators) I Collimator A Collimator B Collimator C DATA MC + + Aug. 04 run 2004年12月17日 Well Reproduced 宇宙線研究所共同利用研究成果発表会 + A B C 7 Arbitrary Unit Source run (g ray injection from collimators) II 137Cs: 10-1 662keV 10-1 DATA MC 10-2 10-3 60Co: 10-2 10-3 ~1/200 1.17&1.33MeV DATA MC ~1/10 10-5 -15 10-5 Reconstructed Z +15cm -15 Gamma rays Z= -15 Z= +15 2004年12月17日 No energy cut, only saturation cut. BG subtracted r=2.884g/cc PMT Saturation region 10-4 10-4 Aug. 04 run Reconstructed Z +15cm Impressive agreements. Self shield works as expected. Photo electron yield ~ 0.8p.e./keV for all volume 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) III Performance of the energy scale stability Relative difference (%) Collimated g ray source run from center hole 60Co, 1132keV 60Co +-0.5% calibration data Peak position from simple gaussian fit Aug. 04 run No degrading of the energy scale Stable within +-0.5% Elapsed day 2004年12月17日 宇宙線研究所共同利用研究成果発表会 9 External background source Background level was estimated from known sources PMTs origin 238U series 40K 232Th 210Pb series in the lead shield [count/keV/day/kg] (=dru) g rays from outside shield MC estimation for full volume These values are based on the measurements by HPGe. Energy (keV) 2004年12月17日 宇宙線研究所共同利用研究成果発表会 10 Background data Event rate (/kg/day/keV) Miss-reconstruction due to dead-angle region from PMTs. MC simulation REAL DATA 3.9days livetime All volume All volume 20cm FV 20cm FV 10cm FV 10cm FV (3kg) (3kg) 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) 2004年12月17日 宇宙線研究所共同利用研究成果発表会 11 Miss reconstruction: dead angle from the PMTs HIT ? HIT 2004年12月17日 Scintillation light at the dead angle from PMTs give quite uniform 1p.e. level HIT signal for PMTs. This cause miss reconstruction as if the vertex is around the center of the detector. HIT Immersing PMTs into LXe HIT and using spherical design solve this problem. It will give low BG in the Inside the chamber is just copper surface ROI for DM search 宇宙線研究所共同利用研究成果発表会 12 Internal background source Current results We observe the Bi-Po decay chain. 238U: = (33±7)x10-14g/g Goal for 1ton detector 1x10-14 g/g Factor ~30, but may decay out further 232Th: < 23x10-14 g/g (In this time, there is no candidate events) Factor <~10 (under further study) Kr: = 3.3±1.1 ppt 2x10-14 g/g 1ppt Almost achieved by the distillation process 2004年12月17日 宇宙線研究所共同利用研究成果発表会 13 222Rn decay out 238U DT < 1ms 222Rn (1.8days) 3.5MeV 214Bi 214Po 210Pb b (Emax=3.3MeV) a (7.7MeV) 67ev t1/2 =164msec DL Aug.04 run preliminary DT: t1/2 = 141+-51msec 2 separate runs to check 222Rn decay (t =3.8day) 1/2 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 ) 2004年12月17日 宇宙線研究所共同利用研究成果発表会 14 Distillation to reduce Kr (1/1000 by 1 pass) Very effective to reduce internal impurities (85Kr, etc.) Processed our Xe before the measurement. Original Xe: ~3 ppb Kr Lower temp. ~1% ~3m Xe 165K Kr 120K Off gas Xe: 330±100 ppb Kr (measured) Operation: 2 atm Processing speed: 0.6 kg / hour Design factor: 1/1000 Kr / 1 pass 13 stage of 2cmf Higher temp. 2004年12月17日 Boiling point (@1 atm) ~99% 宇宙線研究所共同利用研究成果発表会 Purified Xe: 3.3±1.1 ppt Kr (measured after Krenrichment) 15 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 misreconstruction 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) 2004年12月17日 宇宙線研究所共同利用研究成果発表会 16 Current status of LG mounting 2004年12月17日 宇宙線研究所共同利用研究成果発表会 17 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 /kg/day/keV “Full” photo-sensitive,“Spherical” geometry detector external g ray (60cm, 346kg) external g ray: 8x10-5/keV/kg/d (40cm, 100kg ) 80cm Achieved dia. Dark matter (10-6 pb, 50GeV, 100 GeV) ~800-2” PMTs (1/10 Low BG) 70% photo-coverage ~5p.e./keVee 2004年12月17日 Q.F. = 0.2 assumed 7Be pp 0 100 宇宙線研究所共同利用研究成果発表会 200 Energy(keVee) 18 Expected sensitivity 10-4 Cross section to nucleon [pb] 106 SD 104 10-6 102 1 10-8 Edelweiss Al2O3 Tokyo LiF Modane NaI CRESST UKDMC NaI 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 2004年12月17日 宇宙線研究所共同利用研究成果発表会 Plots except for XMASS: http://dmtools.berkeley.edu Gaitskell & Mandic 19 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! 2004年12月17日 宇宙線研究所共同利用研究成果発表会 20
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