ppt

The XMASS experiment
The XMASS Collaboration
Kamioka Observatory, ICRR, Univ. of Tokyo：
Y. Suzuki, M. Nakahata, S. Moriyama, 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
Saga University: H. Ohsumi
Tokai University: K. Nishijima, D. Motoki
Gifu University： S. Tasaka
Waseda University： S. Suzuki
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
Seoul National University： S.B. Kim
Sejong University： Y.D. Kim
KRISS: Y.H. Kim, M.K. Lee, K. B. Lee, J.S. Lee
1. XMASS experiment
¾ What’s XMASS
Multi purpose low-background experiment with liq. Xe
Y. Suzuki et al., hep-ph/0008296
z Xenon MASSive detector for solar neutrino (pp/7Be)
z Xenon neutrino MASS detector (ββ decay)
z Xenon detector for Weakly Interacting MASSive Particles (DM search)
Solar neutrino
Double beta
Dark matter
As a 1st phase, an 800kg detector
for dark matter search is under
construction.
3
¾ 800kg detector
Elec. hut
Water tank
Inner and Outer
OFHC copper
vessel
Refrigerator
11m
857kg
xenon
10m
72 20inch PMTs (veto)
~ 1.2m
642
PMTs
¾ Structure of the 800kg detector
Single phase liquid Xenon detector
z
z
z
z
z
z
857kg of liquid xenon, 100kg in the fiducial volume
642 PMTs (630 hex +12 round)
Hex: R10789-11
Q.E. : 28-39%
Photo coverage: 62.4%
3D event reconstruction
5keVee threshold with 4.4pe/keVee
12
6.
6
58.4
Round: R10789-11MOD
×60
310mm
Φ1113mm
Φ47
1
.6
6
2
Expected sensitivity
Spin Independent Case
N10
O
N
XE
SII
M
CD
σχp>2x10‐45 cm2
for 50‐100GeV WIMP, 90%C.L.
1yr exposure, 100kg FV,
BG: 1x10‐4 /keV/d/kg
Scintillation efficiency: 0.2
Expected energy spectrum
r
y
1
S
S
A
XM
1 year exposure
σχp=10-44 cm2
50GeV WIMP
Black:signal+BG
Red:BG
2. Background reduction
(1) BG from detector materials
z 642 PMTs: Main BG source although RI level is 1/100
of ordinary PMT.
z OFHC copper: Bring in the mine < 1month
after electrorefining (Mitsubishi Material Co.)
z 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).
BG/PMT [mBq]
0.70 +/- 0.28
1.51 +/- 0.31
< 5.10
2.92 +/- 0.16
T
M
P
γ tracking
< 10-4 /keV/day/kg (100kg F.V.)
n contribution < 2.2x10-5/d/kg
keV
Counts/day/kg/keV
PM
T
U chain
Th chain
40K
60Co
Counts/day/kg/keV
¾ Self-shielding for BG from PMTs
keV
(2) External BG (γ, n) from rock
11m
10m
107 n’s
γ
Att. vs.
thickness
n
y [cm]
Reduction of gamma rays
z γ and n from rock are sufficiently reduced by a 2m
thickness pure water tank:
γ < γ from PMT, n << 10-4 /day/kg
z 10m dia. and 11m height water tank for future extensions.
z 72 20’’ PMTs for active veto for CR μ.
water
Liq. Xe
PMT BG level
Î 2m needed
0
1
2
X [cm]
3 (m) 5m dia. = ~2m wall thickness
(3) Internal BG (1) : Kr
z Kr (85Kr: Qβ=687keV, τ=10.8y) can be reduced by distillation.
z Our goal: Kr < 1ppt (
<10-5 /day/keV/kg)
z 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
z Target value can be achieved
Distillation tower
in 10 days for 1ton xenon.
(0.1ppm
1ppt)
commercial
Boiling point
(@0.2MPa)
Xe
178 K
Kr
140~150 K
LXe
intake
GKr
outlet
Kr
LXe
outlet
4m
(4) Internal BG (2) : Rn
z Measured Rn emanation rate from all materials is
< 15mBq
z Our goal: 222Rn < 0.6 mBq/ton (<10-5 /kev/day/kg)
z Continuous Rn removal with xenon circulation is needed.
z Filtering: by gas and liquid. Under study.
Charcoal
Filter
GXe <30 liter‐GXe/m
LXe ~a few liter‐LXe/m
Each components and construction status
Calibration system
Electronics hut
LXe tank
Clean booth
at the entrance
Distillation
Tower
GXe buffer tank
10m3 x 2, <10bar
GXe compressor
Experimental hall, water shield, and gas handling syst.
The PMT holder: construction Nov. 2009
3.7
m
4.0
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
Circulation system
Gas circulation <30L/min
gas
pump
Cable line
filters
Calibration line
Water
tank
XMASS circulation
system
Gas phase: < 30 L/min
Liquid phase: ~ 5 L/min
857kg
Outer vacuum
Condenser
360W
emergency gas pump
100L/min
evaporator
filters
700L
liquid
Liq.
pump
Liquid circulation Storage
~5L/min
10 m3
x2
gas
storage
700 L Liquid xenon reservoir
10m3 emergency
reservoir and compressor.
Compressor
•
•
•
•
•
700L can be contained.
Collect xenon with liquid and keep. •
Vacuum insulation
PTR 180W @-100 degree
•
Liquid nitrogen line.
•
In the case of emergency we can
collect xenon gas by compressor.
1ton, 170m3 xenon gas with 9MPa.
100 L/min flow rate.
•
•
•
•
•
•
Condenser
2 PTR 180W@100degree x2
Estimated heat
invasion to the
detector is ~50W.
Liquid nitrogen line
is also equipped.
Gas circulation <30L/min
gas
pump
Cable line
Calibration
line
Water
tank
857kg
Outer vacuum
filters
Liquid
pump
Max
5L/min
emergency gas
pump
100L/min
evaporato
Condenser
r filters
360W
700L
liquid
Liq.
pump
Liquid circulation Storage
~5L/min
10 m3
x2
gas
storage
• Gas filter
– To remove Rn, use
charcoal
– PTR
• Gas pump
– Max 30L/min
• Evaporator
– To keep Max 30L/min
gas flow.
Gas circulation <30L/min
gas
pump
Cable line
Calibration line
Water
tank
857kg
Outer vacuum
filters
emergency gas
pump
100L/min
evaporator
Condenser
filters
360W
700L
liquid
Liq.
pump
Liquid circulation Storage
~5L/min
10 m3
x2
gas
storage
Calibration system
• Gamma source
– To check
• Position reconstruction
• Energy resolution
– From 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
detector
Linear drive
+ stepping moter
Linear and
rotary drive
source
¾ To introduce calibration source to
inside detector
¾ Operate from the water tank top, 5m
above detector
Gate valve
Liquid xenon
~5m
z Move top PMT and make window
through which source can enter
z Introduce source to inside of the
detector.
z Open/close of the window can be
checked by optical fiber scope.
Top PMT
z Source can be changed even during
observation.
27
Inside of detector
¾ ＰＭＴ drive system
Tank top (atmosphere)
Linear and rotary drive
Constant
force
spring
handle
Rotate
90 degree
Lift up
150mm
Control rod
Inside detector Top PMT
(xenon)
28
Calibration source rod
z φ12mm, length 1560mm,1.54kg
z Lift up and down by φ0.3mm SUS301 wire
z Calibration source is attached at the end of rod.
Source ＋holder Adaptor (SUS304)
(exchangable)
OFHC
29
3. Prepared source
nuclide
energy [keV]
strength
[Hz]
diameter
[mm]
package
material
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
z (1) Fe-55 and (2) Cd-109 are sealed in 50μm thickness brass tube
z Pressurized test (1MPa)
z Leak check at low temperature.
Fe
φ5mm
30
50mm
４．Schedule in near future
9月
10月
Distillation to get rid of Kr
Circulation line construction
20’’ＰＭＴ
Installation in water tank.
•
•
11月
Introduce liquid xenon, circulation and purification
Calibration
Check detector response and xenon quality
Start observation
Distillation and installation of 20’’ PMT have been finished.
Observation will start after confirmation of xenon quality and
detector performance by calibration.
Summary
• XMASS 800kg detector
–
–
–
–
Use 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.
• Construction
– Most parts finished. PMT holder, IVC, OVC.
• Schedule
–
–
–
–
Distillation and installation of 20’’ PMTs finished.
Finishing circulation line.
Introduction of liquid xenon and calibration will be start soon.
After confirmation of detector performance, observation will start.
較正装置の設置 (水タンク上)
ステッピングモータ、
巻取りドラム
ワイヤー
(SUS301, 直径0.3mm)
3m
較正源棒
(無酸素銅、直径12mm,長さ1560mm)
較正源交換窓
ゲートバルブ
(内径40mm)
水タンク上
PMT操作
ハンドル
較正用配管
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
(検出器最下部位置)
36
¾ Rn removal test in gas circulation
Charcoal housing
z Charcoal whose suitable hole size (~10Å)
was selected.
z Tested in -105℃, with 10Bq Rn in xenon.
z More than 85% Rn removal was achieved.
(charcoal weight: 25g, trap length: 60cm, flow rate: 0.5L/min).
Rn removal efficiency is now being improved with more
suitable trap length and flow rate.
z In the case of Rn removal emanated from only gas phase,
our goal (<0.6mBq) can be achieved with 1.0 L/mim flow rate.
z Rn removal emanated from liquid phase is now under study.
4. スケジュール
月
9
検出器の状態
較正
上旬
検出器のタンク内設置完了
タンク外配管作業
z レーザーによるタイミング測定 (終了済)
中旬
検出器真空引き・ベーキング
タンク内 veto PMT取付
キセノン蒸留 (1ton)
下旬
検出器真空引き・ベーキング
タンク水はり試験 (PMT取付)
10 上旬
中旬
下旬
11
検出器冷却・キセノン導入
(getter, evaporator)
z OD PMT 較正 (シンチレータボール)
データ取得
いったん回収
その後、再度導入
(getter, evaporator)
z 外部・内部 γ 較正源を使って光量測定。
キセノンの quality check
z 内部 γ 較正源を使ってパラメータ (吸収・
散乱長等) tuning
z 外部 γ 源を使って wall effect study
長期データ取得
z パラメータ tuning
z 内部LED、外部γ源による daily calib.
検出器安定性を常にモニタ