The XMASS experiment

K. Abe for XMASS collaboration Contents

• – SUSY neutrarino • Approach to dark matter detection – Direct detection – Short explanation for some experiments • The XMASS experiment. – Overview of experiment – Target sensitivity and BG reduction. – Construction of detector. – Detail for some components. – Current status.

Dark Matter Problem – We know how much there is, but don’t know what it is.

Cosmic Microwave Background

NASA/WMAP Weakly Interacting Massive Particle Dark Matter is required to be • Neutral ➡can not see ... • Non-baryonic ➡weakly interacting • Cold (non-relativistic) ➡structure formation dark matter distribution Springel et al. 2005 SUSY ⇒ One of the favored scenario: The lightest SUSY particle is stable and likely becomes a dark matter candidate Linear combination of SUSY particles

~0 ~ ~ ~ ~ c = aBB + aWW + aHuHu + aHdHd Approaches to Dark Matter Detection

q χ

- χ

χ χ χ q q χ

- - q q χ q q χ Direct Indirect Colliders Direct Detection Principle WIMPs elastically scatter off nuclei in targets, producing nuclear recoils.

Dark Matter Deposit Energy （WIMP） χ + N → χ + N • Vsun ~ 220 km/s • Erecoil ~ <100 keV, low energy • Low event rate, less than 1 WIMP/week will collide with an atom in 1kg material Expected Energy Spectrum (SI)

Spin independent case:

Xe (A=131) is one of the best target. WIMP Mass Determination by Direct Detection

-8

10 pb, Ge light

95% solid, 68% dot heavy rate energy

3x103 kg day ~10 WIMPs True 3x104 kg day ~100 WIMPs

3x105 kg day ~1000 WIMPs

A. Green arXiv:0805.1704v2 Techniques for Detector Various Targets: Ge, Xe, Ar, Ne, NaI and so on. Two Signals are used to particle identification to distinguish btw Nuclear Recoil and gamma or beta. Tracking DRIFT, NEWAGE Bubble COUPP, PICASSO CDMS-II EDELWEISS-II Phonon CRESST-II

Erecoil Scintil XMASS, Ionization lation DAMA/LIBRA CoGeNT DEAP/CLEAN

ZEPLIN, XENON WARP, LUX,ArDM List of experiments. • Gran Sasso, Italy – XENON, WARP, DAMA, CRESST • Frejus, France – EDELWEISS • Boulby, England – ZEPLIN, DRIFT • SNOLAB, Canada – DEAP/CLEAN, PICASSO This is not all, there • Fermilab, US – COUPP, CoGeNT exist many running • Homestake, US experiment. – LUX • SOUDAN, US – CDMS, CoGeNT • Kamioka, Japan – XMASS • Yanyang, Korea – KIMS • CJPL, China – PANDAX Short explanation for some experiments. • DAMA/LIBRA – NaI, Scintillation • XENON100 – Xenon, Scintillation and Ionization. • CDMS-II – Ge, Ionization and Phonon. DAMA, positive signal report • NaI(Tl) target. – DAMA/NaI 1996~2002 ~100kg – DAMA/LIBRA 2003~2008 232.8kg – DAMA/LIBRA 2008/11~ 242.5kg • 5x5 array of 9.7 kg NaI(Tl) crystals viewed by 2 PMTs each. • Heavy shield:>10 cm of Cu, 15 cm of Pb + Cd foils, 10/40 cm PE/paraffin, ~1 m concrete DAMA • Annual modulation in 2-6 keV single hits: 8.9 σ • Total single rate ~1 cts/d/kg/keV • Expected annual modulation <3~5%. • Period and phase is about right for expected.

December

60° R. Bernabei et al. EPJ C 56, 333 (2008), arxiv:0804.2741 June EPJ C 67, 39 (2010), arxiv:1002.1028 Recent positive signals • For long time, DAMA was the only experiment who observed positive dark matter signal. • Recently some other groups start to report possible positive signals. • CoGeNT – P-type point contact Germanium detector – Use only ionization signal. – Excess event and 2.8 sigma annual modulation. • CRESST-II – CaWO4, calcium tungstate. – Use scintillation and phonon.

arxiv:1106.0650 Cross Section: Spin Independent Case

Positive signals around light mass… 5 XENON100

• Gran Sasso in Italy • Double Phase Liquid Xenon detector • 161 kg needed to fill the TPC. Active volume 62 kg. • 242 PMTs to observe direct scintillation and ionization signal. • 3D position sensitive TPC Event Discrimination: Electron or Nuclear Recoil

WIMP or Neutron nuclear recoil

Gamma or Electron

electron bottom PMT array recoil CDMS • Soudan Lab in Minnesota • Ge (4.75 kg) and Si (1.1 kg) • Cryogenic, <50mK • Both Ionization and phonon signal • Ionization+phonon timing: Rejects >99.9999% of gammas, >99% of ‘betas’ Cross Section: Spin Independent Case

Start to reach parameter region favored by theory. 5 Spin dependent case neutron-coupling proton-coupling

CDMS II

XENON10

• Odd isotope: natural Xe: 129Xe, 26.4 %, spin 1/2, 131Xe, 21.2%, spin 3/2 • 73Ge (spin-9/2) 7.73% , 29Si (spin-1/2) 4.68% The XMASS experiment

• Overview. • Sensitivity and BG reduction. • Construction. • Detail of some components. • Commissioning status The XMASS collaboration

, ICRR, Univ. of Tokyo： Y. Suzuki, M. Nakahata, S. Moriyama, M. Yamashita, Y. Kishimoto, Y. Koshio, A. Takeda, K. Abe, H. Sekiya, H. Ogawa, K. Kobayashi, K. Hiraide, A. Shinozaki, S. Hirano, D. Umemoto, O. Takachio, K. Hieda  IPMU, University of Tokyo： K. Martens, J.Liu  Kobe University: Y. Takeuchi, K. Otsuka, K. Hosokawa, A. Murata  Tokai University: K. Nishijima, D. Motoki, F. Kusaba  Gifu University： S. Tasaka  Yokohama National University： S. Nakamura, I. Murayama, K. Fujii  Miyagi University of Education： Y. Fukuda  STEL, Nagoya University： Y. Itow, K. Masuda, H. Uchida, Y. Nishitani, H. Takiya  Sejong University： Y.D. Kim 41 collaborators,  KRISS: Y.H. Kim, M.K. Lee, K. B. Lee, J.S. Lee 10 institutes

2014/5/27 22 Kamioka mine at Kamioka, Hida, Gifu

Kamioka observatory Kamioka Observatory

• 1000m under a mountain = 2700m water equiv. • 360m above the sea • Horizontal access • Super-K for n physics and other experiments in deep underground • KamLAND (Tohoku U.)

By courtesy of Dr. Miyoki XMASS experiment ●XMASS ◎ Xenon MASSive detector for Solar neutrino (pp/7Be) ◎ Xenon neutrino MASS detector () ◎ Xenon detector for Weakly Interacting MASSive Particles (DM search) • It was proposed that 10ton FV (24ton) 2.5m 100kg FV (800kg) Liquid was a good Solar n, 0nbb, DM candidate to satisfy 0.8m, DM scalability and low in future First phase background. Y. Suzuki, hep-ph/0008296 • As the first phase, an 800kg detector for a dark matter search was constructed, and is being commissioned.  Why liquid Xe ? • High Atomic mass Xe (A~131) good for SI case (s∝A2). • High abundance of odd isotope (129Xe (26.4%), 131Xe (21.3%)) with large SD enhancement factors. • High atomic number (Z=54) and density (r=~3g/cc) • Effective self-shielding. • Compact for large mass detector. • Relatively high boiling point 178K, easy to handle liquid phase compared to other noble gas (Ar 87K). • High photo yield (~46000 UV photons/MeV at zero field) • Easy to purify for both electro-negative and radioactive impurities. • By circulation of Xe with getter for electro-negative. • Distillation for 85Kr removal.

2014/5/27 26  XMASS detector and water tank

Elec. hut Inner and Outer Water tank OFHC copper vessel Refrigerator

11m 857kg xenon

642 10m PMTs ~ 1.2m 72 20inch PMTs (veto)  Structure of the PMT holder

 OFHC copper  642 PMTs (630 hex +12 round)  Q.E. : 28-39%  Photo coverage: 62.4% Hex: R10789-11  3D event reconstruction  5keVee threshold with 4.4pe/keVee

58.4

Round: R10789-11MOD ×60

310mm Φ47 Φ1113mm Electronics • Analog Timing Modules (ATM) used for Super- Kamiokande record charge and timing of PMTs. • FADCs record waveform of PMTs with 500MHz. Target sensitivity and BG reduction

• How to reduce BG to 10-4 /day/kev/kg level for target sensitivity of 10-45cm2. – Detector material – External, from rock – Internal, from Xenon

 Expected sensitivity Spin Independent -45 2 scp > 2x10 cm for 50-100 GeV WIMP (90%C.L.) 1yr exposure, 100kg FV BG: 1x10-4 /keV/day/kg Q factor: 0.2

Expected energy spectrum 1 year exposure -44 2 scp=10 cm 50GeV WIMP Black:signal+BG Red:BG

2014/5/27 31 Background reduction

(1) BG from detector materials

 642 PMTs: Main BG source although RI level is 1/100 of ordinary PMT.  OFHC copper: Bring in the mine < 1month after electrorefining (Mitsubishi Material Co.)  Other materials: All the components were selected with HPGe and ICP-MS. (>250 samples were measured) The total RI level is much lower than PMT BG.

We developed new ultra low RI PMT with Hamamatsu. (1/100 of ordinary one). g

tracking  < 10

Self - n contribution contribution n < 2.2x10 4

60Co 40K Th chain Uchain

/keV/day/kg (100kg F.V.) - shielding for BG from PMTs

2.92 +/ 5.10 < 1.51 +/ 0.70 +/ BG/PMT [mBq]

- - -

0.16 0.31 0.28 -

5 /d/kg /d/kg

Counts/day/kg/keV Counts/day/kg/keV keV keV

(2) External BG (g, n) from rock

 g and n from rock are sufficiently reduced by a 2m thickness pure water tank: g < g from PMT, n << 10-4 /day/kg  10m dia. and 11m height water tank for future extensions.  72 20’’ PMTs for active veto for CR m.

107 n’s

g Att. vs. n thickness 11m [cm]y water

Liq. Xe PMT BG level

 2m needed Reduction of rays gammaReduction X [cm] 10m 0 1 2 3 (m) 5m dia. = ~2m wall thickness  Internal BG

 External BG (g and n) can be effectively reduced by the water tank and outer part of liq. Xe. On the other hand, Internal BG (radioactive contaminations) need to be reduced by other means.  Possible internal BG sources are 222Rn, 220Rn and 85Kr.

U chain Th chain 222Rn 220Rn

2014/5/27 35 (3) Internal BG (1) : Kr

85  Kr ( Kr: Qb=687keV, t=10.8y) can be reduced by distillation.  Our goal: Kr < 1ppt ( <10-5 /day/keV/kg)  5 order of magnitude reduction with 4.7kg/hr processing time was achieved. K. Abe et al. for XMASS collab., Astropart. Phys. 31 (2009) 290  Target value can be achieved in 10 days for 1ton xenon. Distillation tower (0.1ppm 1ppt) commercial

GKr 4m outlet

Boiling point (@0.2MPa) Kr LXe Xe 178 K outlet Kr 140~150 K (4) Internal BG (2) : Rn

 Measured Rn emanation rate from all materials is < 15mBq  Our goal: 222Rn < 0.6 mBq/ton (<10-5 /kev/day/kg)  Continuous Rn removal with xenon circulation is needed.  Filtering: by gas and liquid. Under study.

Charcoal Filter GXe <30 liter-GXe/m

LXe ~a few liter-LXe/m Water purification system ~5m3/hour <2mBq-Rn/m3

Rn free air generator ~20m3/hour ~a few mBq-Rn/m3 Construction of detector

• Construction of the PMT holder • Start from end of 2009. • Finished at ~Sep. 2010. Construction of the PMT holder from Nov. 2009

3.7 4.0 m m

3.0 m The PMT holder: PMT installation • 642 PMTs are attached during 13 days. • 200g/PMT • ~200kg for all PMTs

The PMT holder: PMT installation

• All PMTs attached, except boundary 30. • Boundary 30 PMTs were attached after connection of upper and lower half. The PMT holder: Connection of two halves

The PMT holder: Fillter attachment. Total 2.8ton: end of Feb. 2010

Manufacturing detector vessel • A challenge: Manufacturing a large flange with soft OFHC copper. Inside: Electropolished • Due to insufficient strength of its neck part, it needed to be reinforced by adding ribs. • It took four months.

Inner vessel chamber

Outer vessel chamber

クリックしてタイトルを入力 • クリックしてテキストを入力

As of Sep. 2010P-01

More detail of some detector components. • Circulation system • Calibration system Outside of water tank

Calibration system Electronics hut

Refrigerator and Circulation system GXe buffer tank Distillation 10m3 x 2, <10bar Tower

LXe tank

Clean booth at the entrance GXe compressor Experimental hall, water shield, and gas handling syst. Circulation system

Gas circulation <30L/min emergency gas gas compressor pump Cable line 100L/min Calibration line filters

Water 10 m3 tank evaporator x 2 Refrigerator 360W filters XMASS circulation 857kg gas Xe system tank Outer vacuum liquid 700L Gas phase: < 30 L/min pump LXe tank Liquid circulation Liquid phase: ~ 5 L/min ~5L/min 700 L Liquid xenon reservoir 10m3 emergency reservoir and compressor.

Gas circulation <30L/min emergency gas gas compressor Cable line pump 100L/min Calibration filters Compressor line Water 3 • 700L can be contained. 10 m tank • Inevaporato the case of emergency x 2 we can • Collect xenon with liquid and keep.Refrigerat collectr filtersxenon gas by compressor. • Vacuum insulation857kg or 360W• 1ton, 170m3 xenongas Xe gas with • PTR 180W @Outer-100 vacuum degree liquid0.9MPa. 700L tank pump LXe • Liquid nitrogen line. Liquid •circulation100 L/min tank flow rate. ~5L/min • Liquid pump • Max 5L/min • Condenser • 2 PTR 180W@- 100degree x2 • Estimated heat invasion to the detector is ~50W. • Liquid nitrogen line is also equipped.

Gas circulation <30L/min emergency gas gas compressor Cable line pump 100L/min Calibration filters line Water 10 m3 tank evaporato x 2 Refrigerat r 857kg or filters gas Xe 360W tank Outer vacuum liquid 700L pump LXe Liquid circulation tank ~5L/min • Gas filter – To remove Rn, use • Gas pump charcoal – PTR – Max 30L/min • Evaporator – To keep Max 30L/min gas flow.

Gas circulation <30L/min gas emergency gas pump pump Cable line 100L/min Calibration line filters

Water 10 m3 tank evaporator x 2 Condenser 857kg 360W filters gas storage Outer vacuum liquid 700L pump Liq. Liquid circulation Storage ~5L/min Calibration system • Gamma source – To check • Position reconstruction • Energy resolution – Introduce to inside and outside of the detector.

• LED – PMT Gain (1pe) – 8 LEDs are attached to the PMT holder.

• Laser + diffuser – PMT Timing Calibration system for inside Linear drive detector + stepping moter  To introduce calibration source to inside detector, operate from the Linear and rotary drive source water tank top, 5m above detector

 Move top PMT and make window Gate valve through which source can enter

Liquid xenon ~5m  Introduce source to inside of the detector.

 Open/close of the window can be checked by optical fiber scope.

 Source can be changed even during observation. 58 Top PMT Inside of detector Constant  ＰＭＴ drive system force Tank top (atmosphere) spring Linear and rotary drive handle Rotate 90 degree

Lift up 150mm

Control rod

Inside detector Top PMT 59 (xenon) Calibration source rod

 f12mm, length 1560mm,1.54kg  Lift up and down by f0.3mm SUS301 wire  Calibration source is attached at the end of rod.

Source ＋holder Adaptor (SUS304) OFHC copper (exchangable) 60 3. Prepared source

nuclide energy [keV] strength diameter package [Hz] [mm] material (1) Fe-55 5.9 350 5 brass (2) Cd-109 22, 25, 88 800 5 brass (3) Am-241 59.5 485 0.15 SUS (4) Co-57 122 100 0.21 SUS

 (1) Fe-55 and (2) Cd-109 are sealed in 50mm thickness brass tube  Pressurized test (1MPa)  Leak check at low temperature. Fe

f5mm 61 50mm Current status of detector

• Commissioning phase. – Calibration – BG confirmation  Detector response at center

Total photo electron  57Co source at the distribution center of detector. real data  The photo electron simulation distribution was reproduced by a simulation well.  High p.e. yield Reconstructed energy 122keV 15.1+/-1.2p.e./keV distribution ~4% rms was obtained. real data  Energy resolution simulation 136keV for 122 keV g was 59.3keV (W-Ka) ~4%(rms)

2014/5/27 63  Performance of the reconstruction

Real Data Simulation  Reconstructed vertices for various positioning of the 57Co source.  Position resolution was as expected by a simulation.

z=0cm: 1.4cm RMS z=±20cm: 1cm RMS (@122keV, g)

2014/5/27 64  Evaluation of Rn • 214Po and 216Po has short life. • Decay of Bi and Po become continuous event with short time delay. • By using timing information, we can tag such continuous event.

U chain Th chain 222Rn 220Rn

2014/5/27 65  222Rn in liq. Xe  Tagged by a short time coincidence between 214 214 Bi and Po (t1/2=164ms).  Result: 8.2+/-0.5mBq. (expected <15mBq)  <-> goal: 1.0mBq -> would be reduced by a circulation of gas phase. (under study) 1st event (214Bi b) 2nd event (214Po a)

Fitting with Tail due to an expected saturation decay curve

100 500 2014/5/27 100066 Time difference (ms)  220Rn in liq. Xe  Tagged by a short time coincidence between 220 216 two a’s ( Rn, Po (t1/2=0.14s)).  Result was consistent with chance coincidence of a of 222Rn.  Upper limit < 0.28mBq (90C.L.) (<-> goal: 0.43mBq)

Consistent with chance coincidence and null hypothesis for 220Rn.

0 500 1000 2014/5/27 67 Time difference (ms) Summary of detector status • Commissioning status – Detector response – BG status • Detector response – Reconstruction works correctly as expected. – Position resolution and energy resolution is similar level as simulation. • BG status – Rn level was calculated from real data as expected. – Now checking many other components. Summary • Dark matter search – Many experiments with many kinds of technique trying to detect signals from dark matter. – Sensitivities start to reach parameter region favored by theory. • XMASS experiment – Detectot • 1ton liquid xenon. • Single phase detector. • Target sensitivity 10-45cm2 • BG level 10-4/keV/kg/day – Background • From detector, material selection and self shielding. • External gamma and neutron, water shield. • Internal, Kr and Rn, distillation and purification. – Commissioning status.

Calibration system (top of tank)

Stepping motor Wire drum

Wire (SUS301, diameter 0.3mm)

Source rod 3m (OFHC copper diameter 12mm, length 1560mm) Source exchange window

Gate valve (inner diameter 40mm) Handle for PMT 水タンク上 controle

Pipe for calibration 較正装置の設置 (検出器内)

較正源棒ガイドパイプ

検出器内 着座センサー

PMTホルダー

較正源棒 73 (検出器最下部位置) Detector cleaning

Filling  Source Data  Collecting Xenon condence

getter 5. Make gas and passing through getter 6. liquefy the xenon

Valve station Liquid xenon tank circulator

2. Transfer liquid xenon Filter housing through circulator. ２F

1. impurity permeates into xenon 3. Filter out dusts by 4. xenon collects to all SUS particle filter liq. xenon tank Calibration system

 Gamma source . To check • Position reconstruction • Energy resolution • Xenon parameter check, transparency, photo yield . From inside and outside of the detector. . Construction of System is already finished.  LED . PMT Gain (1pe) . 8 LEDs are attached to the PMT holder. . LED calibration at room temperature was done at last month.  Laser + diffuser . PMT Timing . Already finished. x, g ray attenuation in LXe - internal source

 Due to short attenuation length (LAtt) of low energy x-ray in liquid Xenon, we need a very small size source for minimum blocking. 2π source 4π source Liquid Xenon x, g ray 109Cd

57Co 55Fe D Scintillation Photons Source itself blocks 241Am the scintillation lights. 1 DL 3 Att 76 CDMS, XENO10, DAMA DAMA/LIBRA •Gran Sasso in Italy • DAMA(~100 kg) + LIBRA (~250 kg) of NaI •Annual Modulation (DAMA 7 yrs + LIBRA 4yrs)

8.3σ C.L.

8.8σ C.L.

December

60° 8.2σ C.L. June • 10-45 XMASS 1T XMASS XMASS 20T XMASS

World Future View XENON10 68% 1 event/100kg/yr 1

1 event/kg/yr 1

proposed near future XENON1t,EURECA,ELIXIR, ... WARP1t, ArDM XMASS20T, SuperCDMS1t, coannihilation region coannihilation region PointFocus ZEPLIN CRESST CDMS Roszkowski et al. hep CMSSM in 2007 - ph 0705.2012v1

- II, II, XENON100,COUPP, - III,... - II, EDELWEISS II,

- II,

 85Kr in liq. Xe Sensitivity of our API-MS (atmospheric pressure ionization mass spectroscopy) 101

Sensitivity Calibration sample 100 ~10ppt Kr=2.7+/-0.6ppb (<->goal: 2ppt) -1 10 BG (He)

10-2 Ion Ion current(nA) Cal x 1/270 (10ppt equiv) 10-3 -3 -2 -1 0 1 Time (min)  Gas chromatography and API-MS started to work (~10ppt sensitivity). More sensitive measurement (<1ppt) using a cold trap is under preparation.  Data analysis to look for a delayed coincidence event is under study. 2014/5/27 80 • 136Xe