XMASS experiment平成２２年度共同利用研究成果発表会
Dec. 17 2010
H.Ogawa for the XMASS collaboration

共同利用-C01
査定金額 30万円(旅費）
使途
共同研究者のための神岡研究施設への旅費

The XMASS Collaboration
Kamioka Observatory, ICRR, Univ. of Tokyo：
Y. Suzuki, M. Nakahata, S. Moriyama, Y.Kishimoto, M.
Yamashita, Y. Koshio,
A. Takeda, K. Abe, H. Sekiya, H. Ogawa, K. Kobayashi, K.
Hiraide,K. Ueshima, A. Shinozaki, H. Nishiie, S. Hirano
IPMU, University of Tokyo： K. Martens, J.Liu
Kobe University: Y. Takeuchi, K. Otsuka
Tokai University: K. Nishijima, D. Motoki
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
Sejong University： Y.D. Kim
KRISS: Y.H. Kim, M.K. Lee, K. B. Lee, J.S. LeeXMASS experiment
What is XMASS?
Multi purpose low-background and low-energy threshold experimentwith liquid Xenon
 Xenon detector for Weakly Interacting MASSive Particles (DM search)
 Xenon MASSive detector for solar neutrino (pp/7Be)
 Xenon neutrino MASS detector (bb decay)

Solar neutrino

Double beta

Dark matter
Dark Matter（WIMP）

Deposit Energy

Xenon
3

Three phases of the XMASS
experiment
100kg Prototype（FV:30kg, ~30cm）

800kg Detector（FV:100kg, 80cm）

20ton Detector（FV:10ton, ~2.5m）

Dark Matter

Solar Neutrino
Dark Matter

Completed
R&D

2007: Project was funded.
2010 Nov.-: Xenon filling was completed
4

Expected sensitivity
Spin Independent Case

scp>2x10-45 cm2for 50-100GeV
WIMP, 90%C.L.
1yr exposure, 100kg FV,
BG: 1x10-4 /keV/d/kg
Scintillation efficiency:
0.2
Expected energy spectrum
1 year exposure
scp=10-44 cm2
50GeV WIMP

Black:signal+BG
Red:BGMCXMASS detector (from outside)※Water tank and external background reduction:
 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.

Refrigerator

10m
72 20inch PMTs (veto)

107 n’sgAtt. vs.
thicknessy [cm]

11m

Elec. hut
Reduction of gamma rays

Water tanknwaterMCLiq. Xe
PMT BG level 2m needed

MCX [cm]0123 (m) 5m dia. = ~2m wall thickness

XMASS detector (main)
OFHC coppervessel

857kg
xenon

~ 1.2m642
PMTs※We developed new ultra low
RI PMT with Hamamatsu.
(1/100 of ordinary one).
Hex: R10789-11

Round: R10789-11MOD

Φ47

U chainTh chain
40K
60Co

Counts/day/kg/keV

 Self-shielding for BG from PMTs (MC)BG/PMT [mBq]0.70 +/- 0.28
1.51 +/- 0.31
< 5.102.92 +/- 0.16

MCkeV

g tracking< 10-4 /keV/day/kg (100kg F.V.)
n contribution < 2.2x10-5/d/kg

Counts/day/kg/keV

MCkeV

Cryogenic
XMASS circulation system

Gas phase: < 30 L/min
Liquid phase: ~ 5 L/min

700L liq.storage

Gas circulation <30L/min
emergency gas
pump
100L/mingas
pump

Cable line
Calibration line

gettergetterWatertankxenon
Outer vacuum

evaporator
Condenser
360W
filters

liquidpump
Liquid circulation~5L/min

700L
Liq.
Storage

10 m3x2gas
storage

Liquid pumpElectronics※Previously used in super Kamiokande12bit ADC/TDC (ATM)Pre-amp card
(modified for XMASS)

PMT

Large energy range are covered• TKO module• ADC dynamic range : 0~400 pC• TDC dynamic range : 0~1 usec

8bit Flash ADC
For pulse shape discrimination
in low energy• dynamic range: 0~-1 V• sampling rate : 500 MS/s
• sample number:
8,160• time span : 16.32 usec
10

Calibration

Source introduce machine

Calibration sources
RIenergy[keV]Intensity [Hz]

φ [mm]

package(1) Fe-55

5.9

350

5brass(2) Cd-109

22, 25, 88

800

5brass(3) Am-241

59.5

485

0.15SUS(4) Co-57

122

100

0.21

SUS

Source rod

Top PMT movingmachine

Gate valve

Xenon gas area~5m

RI source with holder adaptor(SUS304) OFCUTop PMT(removed between calibration)

Detector Construction Nov. 2009Sep 2010

Construction of the PMT holder: Nov. 2009

PMT installation: 311 for each half, 40 forboundary 2009-2010

Cabling: 642 pairs of a coax and HV cable, each 13m
lengthJoining two halvesFiller attachment. Total 2.8ton: end of Feb. 2010

Closing the detector
Working inside clean booth

Closing the detector and OVC

Manufacturing detector vessel• A challenge: Manufacturing
a large flange with soft
OFHC copper. Inside:
Electropolished• Due to insufficient strengthof its neck part, it needed tobe reinforced by adding ribs.

All preparation was ready in Sep.2010
Calibration system

Electronics hut

LXe tank

Clean boothat the entranceDistillation
Tower

GXe buffer tank
10m3 x 2, <10bar

GXe compressor

Progress in last three months
Sep.

Oct.

Gas/liquidplumbing
Operation of 700L tank20’’ PMT
installation

Nov.

Calibration(RI source LED)1) Baking2) put purified gas
and drain liquid.

Electronics full installation

With under work :Reconstruction,
Noise reduction,
Radon rate etc…
Commissioning

Detectorcleaning
Distillation

Rn reduction study
Xenon purification

Xenon purification
Kr <1ppt
Distillation

H2O <1ppb(target)
bakingMolecular sieves
GetterXenon draining

Radon<1.2mBq/all(target)
Charcoal

H2 <0.16ppbw
Room temp.Getter
U/Th <10-14g/g(target)
Getterevaporation
RI background

Particle <mg/all(target)
Particle filter
Xenon draining

Light absorption background
Target transparency >>mN2,O2,CO2, CO etc<1ppb(target)
MS, getter※device has been already worked※All values are our target value

Internal BG (1) : Kr

Completed in 2010 Sep.

 Kr (85Kr: 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
Distillation tower
in 10 days for 1ton xenon.
(0.1ppm1ppt(Our goal))commercial

Boiling point(@0.2MPa)
Xe178 KKr

140~150 K

LXe
intakeGKroutlet

KrLXeoutlet

Kr4m

Internal BG (2) : Rn

Under study Measured Rn emanation rate from all materials is< 15mBq Our goal: 222Rn < 1.2 mBq/ton (<2x10-5 dru (/kev/day/kg))
 Continuous Rn removal with xenon circulation is needed.
Gas phase removal :Cooled charcoal can take Rn.
Rn removal system will be mounted
in gas line.

liquid phase removal :Liquid circulator and filter will be used.
But removal method (material) is understudy.
Particle problem remains.
We need more study.
If liquid removal is successful, We cantake Rn speedy than gas removal

Detector cleaning : Drain the xenon from detector
10/19- & 10/26Start xenon filling from storage to detector~9kg/hr

10/24 & 10/31
Xenon filled in detector with 1136kg1,7)Make gas and passing getter

2,8）liquefy the xenon
getterXenon condence

Liquid xenon storage tank

Valve station

circulator

4) Liquid xenon transfer using
Circulator.
3）impurity take to xenon

Filter housing5）take dust by
all SUS particle filter２F6）xenon collects toliq.xenon tank

10/25,2010 : liquid xenon was drained to storage ~300kg/hr

By this work, light yield increased about 16% (form 57Co source data)summary• The XMASS project aims to observe pp solar
neutrinos, neutrinoless double beta decay, anddark matter signals. The 800kg detector is thefirst phase of the project.
• It is expected to have low background of 1x10-4
keV-1 d-1kg-1 in the 100kg FV and sensitivity forSI down to 2x10-45cm2 with one year operation.
• We are now in the commissioning phase. Xenon
draining work improved the total light yield ~16%