1. XMASS Y. Suzuki (for the XMASS Collaboration) Kamioka Observatory,
Institute for Cosmic Ray Research,
and
Institute for the Physics and Mathematics of the Universe,
The University of Tokyo
August 19, 2008
IDM2008, Stockholm, Sweden
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

2. Y.Suzuki, IDM2008, Stckholm, Sweden
XMASS
Ref: Y. Suzuki et al., hep-ph/ , (2000).
Multi-purpose astro-partcle and neutrino experiment
10 ton fiducial mass
(2.5 m in diameter (24 tons))
Dark Matter
Solar pp-neutrinos
Double beta decay
First phase:
100kg fiducial mass
(0.8 m in diameter (850kg))
n+en+e
136Xe 136Ba+2e
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

3. Y.Suzuki, IDM2008, Stckholm, Sweden
Phase I detector
1PMT
Single phase liq. Xe
Pentakis-dodecahedron
 12 pentagonal pyramids
Each pyramid  5 triangles
Radius: 39~42 cm
642 Hex. PMT immersed in liq. Xe
PMT photo-cathode coverage: 64%
Inner mass of Xenon:
857kg (~3g/cm3)
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

4. Y.Suzuki, IDM2008, Stckholm, Sweden
Detector
PMT and Mockup
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

5. Aim, Signal and Backgrounds
10-4 dru (ev/kg/keV/day)
 10-45cm2 SI for ~100GeV WIMPs
For the signal detection
Low threshold: ~ 5 keV or less
 8 pe /keV (64% photo-cov.)
Large fiducial volume: 100kg or more
20cmf: 100kg
(20cm self-shield)
25cmf: 200kg
(15cm self-shield)
before any PSD applied
Expected signal for cm2
for 50GeV / 100GeV
Background level
in 20cm fiducial mass
of 100kg
pp-solar n
7Be solar n
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

6. Aim, Signal and Backgrounds
Challenge to
Reduce Backgrounds
Internal BG (U, Th, Rn, Kr,,,)
Target:
U/ Th < 10-14g/g, Kr <1 ppt
External BG (g, n from PMT, Shields, Rocks)
Self-Shield
Low BG PMT (~1mBq / PMT）、Low BG shielding material
Water Shield surrounding the Xe detector
n/g from rocks
Cosmo-genics
Active muon veto (water shield), Circulation
10-4 dru
U-chain gamma rays
Blue : g tracking
Pink : whole liquid xenon
Deep pink : fiducial volume
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

7. What we have done and status
Basic performance and qualities were already tested using a proto-type detector (30cm)3 and other devices.
1. Reconstruction of the vertex and energy
2. Self-shielding power
3. Various BG
4. Parameters for MC simulation
5. Others
Proto-type detector
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

8. Vertex and energy reconstruction
Vertex reconstruction
 Hit Pattern (+ photon distribution)
External g-ray source
at various positions
tested by the proto-type detector
DATA MC
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

9. Vertex and energy reconstruction
Position resolution
Energy resolution
@10keV
Fiducial
volume
Vertex resolution: 6.5 cm Energy resolution: 1.5 keV for 10 keV events
10keV
R=5cm
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

10. Y.Suzuki, IDM2008, Stckholm, Sweden
Internal Backgrounds
U/Th contamination in liq. Xenon
238U = (9±6) x10-14 g/g (proto-type det.)
Target: 238U < 1x10-14 g/g
(~1decay/100kg/d)
232Th < 23 x10-14 g/g (proto-type det.)
Target: 232Th: <2x10-14 g/g
U, Th near to the goal. within reach.
 Will be reduced further by getters and filters
 Developing new hand-made Molecular Sheaves
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

11. Y.Suzuki, IDM2008, Stckholm, Sweden
Internal Backgrounds
Krypton (85Kr)
To be removed by distillation
made a prototype distillation system
Off-gas Xe:
330±100 ppb Kr
(measured)
Low T
Xenon
w/3ppb Kr
~1%
Process Speed 0.6 kg/h
1/1000 Kr / 1 pass
~3m
~99%
Purified Xe:
3.3 ±1.1 ppt Kr
High T
Target: Kr: < 1ppt
 developing new one
Rn can also be reduced by distillation
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

12. Y.Suzuki, IDM2008, Stckholm, Sweden
External Backgroud
Development of low BG PMT
1/10 of
R8778
(except
60Co)
238U
232Th
40K
60Co
Target (mBq/PMT)
x10-3
x10-3
x10-2
x10-3
Measured (mBq/PMT)
< 1.00
< 0.94
< 0.97
4.5±0.3
~ Achieved the target value
10 cm self-shield
Background from PMTs (238U)
/day/keV/kg
Monte Carlo
Abs . length 100cm
Scat. length 30cm
10-1
10-2
10-3
10-4
10-5
Energy (keV)
Self-shield is very effective
Below 300 keV
number of events in the 20 cm fiducial volume (100kg) decreases rapidly.
<10-5/day/keV/kg
20cm self-shield
(100kg fid. Mass)
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

13. Distance from the entrance (cm)
External Backgroud
Tested ‘Self-Shield’:
by the proto-type detector
g-rays
Z= 0
Z= 30
137Cs: 662keV g-ray
Confirmed Self-Shield works
>2 orders of magnitude agreement between data and Monte Carlo
DATA MC
Number of events
1/200 reduction
in 25cm
g-ray direction
Distance from the entrance (cm)
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

14. Y.Suzuki, IDM2008, Stckholm, Sweden
Neutron backgrounds
Neutrons from rocks
Water shields
effective to reduce neutrons
fn(Kamioka)=
( ) x10-6 /cm2/sec
n events in Liq. Xenon w/ 200cm water
<< 10-4 counts/day/kg
10MeV neutrons
200cm
XMASS water tank
water
Z [cm]
Liq. Xe
Detector Size
~1.5m
MC :
Generation:107
~10m
~4.25m
X [cm]
~10m
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

15. Y.Suzuki, IDM2008, Stckholm, Sweden
Neutron backgrounds
Neutrons from PMT
(a, n) reaction
Spontaneous fission of 238U
Scaled from M.J. Carson, et al., hep-ex/
857kg Xenon + 642new Hex. PMTs U
[ppb] Th
mass
[/PMT]
Rate(U)
[/kg/year]
Rate (Th) [/kg/year]
Quarts
<0.79
<1.69
11 g
<0.002
<0.0008
Metals
<0.18
<0.96
123 g
<0.003
Total < /kg/year (< 2.2×10-5　/kg/day)
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

16. Cavity was completed in February this year
New Experimental Hall
Cavity was completed in February this year
KamLAND
SuperK
H=15m
New Halls
L=21m
W=15m
Water tank will be constructed by next February
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

17. Y.Suzuki, IDM2008, Stckholm, Sweden
New Experimental Hall
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

18. Cross section to nucleon (pb)
Expected results
XMASS (100kg, 5yr) 3s discovery lines:
x ~100 sensitive than the best
10-40 SI
Plots exept for XMASS
Gaitskell & Mandic
Spin Dependent(SD)
DAMA
10-30
10-42
10-32
XENON10
Cross section to nucleon (pb)
10-34
10-44
XMASS
10-36
10-46
10-38
J Ellis et al. benchmark
103
WIMP mass(GeV)
10-40
10-45cm2 (10-9pb) for SI and
10-39cm2 (10-3pb) for SD
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

19. Y.Suzuki, IDM2008, Stckholm, Sweden
Summary
XMASS was fully funded last year
Experimental Hall was completed in the last Feb.
Most of the R&D have finished
PMT
Distillation
filter
We have 1.1 tons of Xenon in Kamioka already
XMASS will be ready by the next summer, 2009.
The BG level in 100~200 kg fiducial volume is expected to be less than 10-4 dru
The target sensitivity is cm2 for ~100GeV WIMPs (SI)
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

20. XMASS Collaborating Institutions
Kamioka Observatory, ICRR, Univ. of Tokyo
Tokai Univ.
Gifu Univ.
Waseda Univ.
Yokohama National Univ.
Miyagi Education Univ.
Institute for Solar Terrestrial Environment, Nagoya Univ.
Seoul National University
Sejong University
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

21. Y.Suzuki, IDM2008, Stckholm, Sweden
Backup
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

22. Y.Suzuki, IDM2008, Stckholm, Sweden
Why single phase
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden

23. Road to Bigger Detector
Fast neutrinos having single recoil interactions will be the ultimate background source in order to go beyond the sensitivity level of 10-45cm2 (10-9pb).
Self-Shield (for neutrons) is extremely important for such backgrounds.
23 tons, 250cm in diameter
Effective volume
5 MeV Neutrons
Interaction point (Evis>5keV)
Effective
Volume
# of events (cm-3) 60
120 cm
Distance from Center
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden 23

24. Y.Suzuki, IDM2008, Stckholm, Sweden
Circulation System
2008/8/19
Y.Suzuki, IDM2008, Stckholm, Sweden