xmass experiment and its double beta decay option xmass experiment for dark matter search and low...

Download XMASS experiment and its double beta decay option XMASS experiment for dark matter search and low energy solar neutrino detection Double beta decay option

Post on 17-Jan-2016

216 views

Category:

Documents

2 download

Embed Size (px)

TRANSCRIPT

  • XMASS experiment and its double beta decay option XMASS experiment for dark matter search and low energy solar neutrino detection Double beta decay option18th Sep. 2005,HAW05 workshop,Double beta-decay and neutrino massesS. Moriyama, ICRR

  • 1. IntroductionDark matterDouble beta Whats XMASS Xenon MASSive detector for solar neutrino (pp/7Be) Xenon detector for Weakly Interacting MASSive Particles (DM search) Xenon neutrino MASS detector (bb decay)

    Multi purpose low-background experiment with liq. Xe

  • Why Liquid Xenon?General properties:Large scintillation yield (~42000photons/MeV ~NaI(Tl))Scintillation wavelength (175nm, direct read out by PMTs)Higher operation temperature (~165K, LNe~27K, LHe~4K)Compact (r=2.9g, 10t detector ~ 1.5m cubic) Not so expensiveWell-known EW cross sections for neutrinos

    External gamma ray background:Self shielding (large Z=54)

    Internal background:Purification (distillation, etc)No long-life radio isotopes Isotope separation is relatively easyNo 14C contamination (can measure low energy)Circulation

  • Key idea: self shielding effect for low energy signalsLarge Z makes detectors very compactLarge photon yield (42 photon/keV ~ NaI(Tl)) Liquid Xe is the most promising material. PMTsSingle phaseliquid XeVolume for shieldingFiducial volume23ton all volume20cm wall cut30cm wall cut (10ton FV)BG normalized by mass1MeV02MeV3MeVExternal g ray from U/Th-chain

  • Strategy of the XMASS project~1 ton detector(FV 100kg)Dark matter search~20 ton detector(FV 10ton)Solar neutrinosDark matter searchPrototype detector (FV 3kg) R&D~2.5m~1m~30cmGood resultsConfirmation of feasibilities of the ~1ton detectorDouble beta decay option?

  • 3kg FV prototype detectorIn theKamioka Mine(near the Super-K)Gamma ray shieldOFHC cubic chamber Demonstration of reconstruction, self shielding effect, and low background properties.16% photo-coverageHamamatsuR8778

  • Vertex and energy reconstructionL: likelihoodm: F(x,y,z,i) x total p.e. S F(x,y,z,i)n: observed number of p.e. === Background event sample === QADC, FADC, and hit timing information are available for analysisF(x,y,z,i): acceptance for i-th PMT (MC)VUV photon characteristics:Lemit=42ph/keVtabs=100cmtscat=30cm Calculate PMT acceptances from various vertices by Monte Carlo. Vtx.: compare acceptance map F(x,y,z,i) Ene.: calc. from obs. p.e. & total accept.ReconstructedhereFADCHit timingQADCReconstruction is performed by PMT charge pattern (not timing)

  • Source run(g ray injection from collimators) IWell reproduced.DATAMCCollimator ACollimator BCollimator C

  • Source run(g ray injection from collimators) IIGood agreements.Self shield works as expected.Photo electron yield ~ 0.8p.e./keV for all volumeGamma raysZ= +15Z= -15137Cs: 662keVDATAMCPMTSaturationregion-15+15cm-15+15cm~1/200~1/10Reconstructed ZReconstructed ZArbitrary Unit10-110-210-310-410-510-110-210-310-410-560Co: 1.17&1.33MeV DATA MCNo energycut, onlysaturation cut.BG subtractedr=2.884g/cc

  • Background dataMC uses U/Th/K activity from PMTs, etc (meas. by HPGe).Good agreement (< factor 2)Self shield effect can be clearly seen.Very low background (10-2 /kg/day/keV@100-300 keV)REAL DATAMC simulationAll volume20cm FV10cm FV(3kg)All volume20cm FV10cm FV(3kg)Miss-reconstruction due to dead-angle region from PMTs.10-2/kg/day/keVAug. 04 run3.9dayslivetime~1.6Hz, 4 fold, triggered by ~0.4p.e.Event rate (/kg/day/keV)

  • Internal background activitiesCurrent results238U(Bi/Po): = (33+-7)x10-14 g/g

    232Th(Bi/Po): < 63x10-14 g/g

    Kr: < 5ppt

    Factor

  • Distillation to reduce Kr (1/1000 by 1 pass)Very effective to reduce internal impurities (85Kr, etc.)We have processed our Xe before the measurement.~3m13 stage of Operation: 2 atmProcessing speed: 0.6 kg / hourDesign factor: 1/1000 Kr / 1 passLower temp.Higher temp.~1%2cmf~99%Purified Xe: < 5 ppt Kr (measured after Kr-enrichment)Off gas Xe:330100 ppb Kr(measured)Original Xe: ~3 ppb Kr

    Boiling point (@1 atm)Xe165KKr120K

  • 1 ton (100kg FV) detector for DM SearchSolve the miss reconst. prob. immerse PMTs into LXeExt. g BG: from PMTs Self-shield effect demonstratedInt. BG: Kr (distillation), Radon Almost achievedexternal g ray (60cm, 346kg)external g ray:(40cm, 100kg )/kg/day/keVDark matter(10-6 pb, 50GeV,100 GeV)Q.F. = 0.2 assumedpp7Be8x10-5/keV/kg/dFull photo-sensitive,Spherical geometry detector80cm dia.0100200Energy(keVee)~800-2 PMTs (1/10 Low BG) 70% photo-coverage ~5p.e./keVee

  • More detailed geometrical design A tentative design (not final one) 12 pentagons / pentakisdodecahedronThis geometry has been coded in a Geant 4 based simulator Hexagonal PMT~50mm diameter Aiming for 1/10 lower BG than R8778 R8778: U 1.80.2x10-2 Bq Th 6.91.3x10-3 Bq 40K 1.40.2x10-1 Bq

  • Expected sensitivityLarge improvements expected.XMASS(Ann. Mod.)XMASS(Sepc.)Edelweiss Al2O3Tokyo LiFModane NaICRESSTUKDMC NaINAIADXMASS FV 0.5ton yearEth=5keVee~25p.e., 3s discoveryW/O any pulse shape info.10-610-410-810-10Cross section to nucleon [pb]10-410-21102104106Plots except for XMASS: http://dmtools.berkeley.eduGaitskell & Mandic

  • Double beta decay option

  • BG for double beta decay signals with conventional XMASS detector2nbb not yet observed. NA 8.9%Q=2.467MeV, just below 208Tl 2.615MeV g raysSelf shielding of liquid xenon is not very effective for high energy g rays.g rays from rock & PMTs need to be shielded.

  • One of possible solutionsPut room temperature LXe intoa thick, acrylic pressure vessel (~50atm).Wavelength shifter inside the vessel.We already have 10kg enriched 136Xe.Merit: Xe can be purifiedeven after experiment starts!

  • Expected sensitivityAssume acrylic material U,Th~10-12g/g, no other bg.Cylindrical geom. (4cm dia. LXe, 10cm dia. Vessel)10kg 136Xe42000photon/MeV but 50% scintillation yield, 90% eff. shifter, 80% water transp., 20% PMT coverage, 25% QE 57keVrms @ Qbb=2.48MeV1yr, 10kg measurement 1.5 x 1025 yr =0.2~0.3eVc.f. DAMA > 7 x 1023 yr (90%)If U/Th ~ 10-16 g/g + larger mass ~0.02-0.03eV2nbb will not be BG thanks to high resolution!!57keVrmsexpectedU+Th normalized for 10kg, 1yr

  • R&D itemsPressure testWavelength shifterScintillation yieldPossible creep effect on acrylic materialDegas from acrylic surfaceBG consideration (time anal., plastic scinti. vessel)Detector designc.f. wavelength shifter: M.A.Iqbal et al., NIMA 243(1986)459 L. Periale et al., NIMA 478(2002)377 D. N. McKinsey et al., NIMB 132 (1997) 351-

  • Pressure test vesselTest vessel held 80 atm water!!valve110mm-dia.120mm length50mm-dia., 50mm length~98ccwater

  • R&D study for wavelength shifterDC light source: excimer xenon lamp

    Vacuum vessel, signal PMT and monitor PMT Vacuum vessel ~80cm diameter Signal and monitor PMTsR8778 for XMASS Sample fixed in 50mm dia. holder Beam splitter: MgF2 tilted by 45 deg.172nmmonitor PMTPMTsample0100160170180190 l (nm)Wavelength ~ LXe scintillation lightArbitrary unit

    Graph3

    0.1533653846

    0.1579807692

    0.1629807692

    0.1679807692

    0.1747115385

    0.18375

    0.1928846154

    0.2032692308

    0.2207692308

    0.2541346154

    0.3159615385

    0.4339423077

    0.64125

    1.0026923077

    1.5586538462

    2.3820192308

    3.5524038462

    5.1211538462

    7.1201923077

    9.5584615385

    12.5394230769

    15.9961538462

    20.0228846154

    24.4530769231

    29.4319230769

    34.6760576923

    40.3443269231

    46.1491346154

    51.8877884615

    57.8414423077

    63.6009615385

    69.1239423077

    74.7338461538

    79.3317307692

    83.8617307692

    87.6695192308

    91.6277884615

    94.4166346154

    96.8428846154

    98.7329807692

    99.7975961538

    100.0976923077

    100.0649038462

    99.3726923077

    98.0431730769

    96.2199038462

    93.7663461538

    91.0913461538

    88.12875

    84.7599038462

    81.0433653846

    77.3664423077

    73.1668269231

    68.9867307692

    64.5580769231

    60.3406730769

    56.2580769231

    52.1557692308

    47.9071153846

    44.1551923077

    40.4674038462

    36.8060576923

    33.5001923077

    30.1599038462

    27.1739423077

    24.4425

    21.9152884615

    19.5827884615

    17.4130769231

    15.5034615385

    13.6963461538

    12.0827884615

    10.6763461538

    9.4064423077

    8.2641346154

    7.2517307692

    6.3168269231

    5.5435576923

    4.8392307692

    4.2411538462

    3.6944230769

    3.2416346154

    2.8477884615

    2.5036538462

    2.2056730769

    1.9517307692

    1.7302884615

    1.5281730769

    1.3617307692

    1.2174038462

    1.0869230769

    0.9725

    0.8684615385

    0.7792307692

    0.7046153846

    0.6435576923

    0.5848076923

    0.5395192308

    0.4932692308

    0.45375

    0.4240384615

    Sheet1

    WL(nm)DataMgF2 Transe

    1500.15336538460.8240.1263730769

    150.50.1579807692

    1510.16298076920.8290.1351110577

    151.50.1679807692

    1520.17471153850.8350.1458841346QEUV

    152.50.18375164.817.1963.60.22877697843.932676259

    1530.19288461540.8420.162408846217023.7699.80.35899280588.5296690647

    153.50.203269230817525.56810.29136690657.4473381295

    1540.22076923080.8480.1872123077182.326.2825.50.09172661872.4105755396

    154.50.2541346154187.924.486.310.02269784170.5556431655

    1550.31596153850.8540.2698311538193.722.051.40.00503597120.1110431655

    155.50.433942307720019.890.420.00151079140.0300496403

    1560.641250.8590.5