Jing LIU IPMU Univ of Tokyo TAUP2011 Munich XMASS collaboration Kamioka Observatory ICRR Univ of Tokyo Y Suzuki M Nakahata S Moriyama M Yamashita Y Kishimoto Y ID: 618604
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Slide1
The XMASS 800kg Experiment
Jing LIUIPMU, Univ. of TokyoTAUP2011, Munich
XMASS collaboration:
Kamioka
Observatory, 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
KRISS:
Y.H. Kim, M.K. Lee, K. B. Lee, J.S. LeeSlide2
The XMASS Experiment
XMASS 800kg
Jing LIU @ TAUP2011
2
Xenon
MASSive
detector for Solar neutrino (pp/
7
Be)
Xenon neutrino MASS detector (double beta decay)
Xenon detector for weakly interacting
MASSive Particles
~100 kg LXeprototype
~800 kg LXedirect dark matter search
~26 ton LXeMulti-purpose
LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe
PMT
LXe insideSlide3
The XMASS Experiment
XMASS 800kg
Jing LIU @ TAUP2011
3
Xenon
MASSive
detector for Solar neutrino (pp/
7
Be)
Xenon neutrino MASS detector (double beta decay)
Xenon detector for weakly interacting
MASSive Particles
~100 kg LXeprototype
~800 kg LXedirect dark matter search
~26 ton LXeMulti-purpose
LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe
PMT
LXe inside
, n,
,…
or
?
PMT
LXe
scintillationSlide4
The XMASS Experiment
XMASS 800kg
Jing LIU @ TAUP2011
4
Xenon
MASSive
detector for Solar neutrino (pp/
7
Be)
Xenon neutrino MASS detector (double beta decay)
Xenon detector for weakly interacting
MASSive Particles
~100 kg LXeprototype
~800 kg LXedirect dark matter search
~26 ton LXeMulti-purpose
LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe
PMT
LXe inside
PMT
LXeSlide5
The XMASS Experiment
XMASS 800kg
Jing LIU @ TAUP2011
5
Xenon
MASSive
detector for Solar neutrino (pp/
7
Be)
Xenon neutrino MASS detector (double beta decay)
Xenon detector for weakly interacting
MASSive Particles
~100 kg LXeprototype
~800 kg LXedirect dark matter search
~26 ton LXeMulti-purpose
LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe
PMT
LXe insideSlide6
The XMASS Experiment
XMASS 800kg
Jing LIU @ TAUP2011
6
Xenon
MASSive
detector for Solar neutrino (pp/
7
Be)
Xenon neutrino MASS detector (double beta decay)
Xenon detector for weakly interacting
MASSive Particles
~100 kg LXeprototype
~800 kg LXedirect dark matter search
~26 ton LXeMulti-purpose
LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe
PMT
LXe insideSlide7
The XMASS Experiment
XMASS 800kg
Jing LIU @ TAUP2011
7
Xenon
MASSive
detector for Solar neutrino (pp/
7
Be)
Xenon neutrino MASS detector (double beta decay)
Xenon detector for weakly interacting
MASSive Particles
~100 kg LXeprototype
~800 kg LXedirect dark matter search
~26 ton LXeMulti-purpose
LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe
PMT
LXe insideSlide8
Structure of XMASS 800kg detector
XMASS 800kg
Jing LIU @ TAUP2011
8
PMTSlide9
Structure of XMASS 800kg detector
XMASS 800kg
Jing LIU @ TAUP2011
9
PMT
Pentakis
dodecahedron
~10 PMTs in one triangle
642 PMTs in total
~0.8 meter
PMT photo-cathodes cover ~62% inner surfaceSlide10
Reconstruct interaction point from PMT hit pattern
XMASS 800kg
Jing LIU @ TAUP2011
10
Colored photo cathodes indicating number of
p.e
. (photoelectrons) recorded by PMTs
Interaction point (vertex) can be reconstructed from the PMT hit pattern. Slide11
LXe self-shielding
XMASS 800kg
Jing LIU @ TAUP2011
11
Simulation:
g
into
LXe
water
LXe
E
[
keV]
Attenuation
length of
[cm]Slide12
Where is it?
XMASS 800kg
Jing LIU @ TAUP2011
12
1000 m rock overburden
(2700 m water equiv.):
Muon
: 6.0x10
-8 /cm
-2/s/sr
Neutron: 1.2x10-6/cm
-2/s360m above the seaHorizontal access:15 minutes drive from office,too easy to get in!No excuse to avoid 24-hour shift Kamioka underground observatorySlide13
XMASS 800kg
Jing LIU @ TAUP2011
13
New experimental hall, Aug. 2008
15 meter
15 meter
20 meterSlide14
XMASS 800kg
Jing LIU @ TAUP2011
14
water tank, Nov. 2008
10 m x 10 mSlide15
XMASS 800kg
Jing LIU @ TAUP2011
15
Frame of clean room in water tank, Mar. 2008Slide16
XMASS 800kg
Jing LIU @ TAUP2011
16
PMT mounting in clean room, Dec. 2009Slide17
XMASS 800kg
Jing LIU @ TAUP2011
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PMT mounting finished, Feb. 2010Slide18
XMASS 800kg
Jing LIU @ TAUP2011
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Water filling, Sep. 2010Slide19
XMASS 800kg
Jing LIU @ TAUP2011
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Commissioning started, Nov. 2010Slide20
Scintillation light yield :: calibration system
XMASS 800kg
Jing LIU @ TAUP2011
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Top PMT can be pulled out
Source changed here
Z position of source is controlled by a motor on top at <1 mm accuracy
x
y
z
57
Co,
241
Am,
109
Cd,
55Fe, 137Cs
F~
4mm
F~
0.15mm
for
57
CoSlide21
Scintillation light yield: 15.9
1.2
p.e
./
keV
(
57Co at center)
XMASS 800kgJing LIU @ TAUP2011
21
DataMC
122
keV136 keV59.3
keV (W)
Number of photoelectronsArbitrary unitSlide22
Position & energy resolution (
122keV
g
from
57
Co)
Data
Reconstructed vertices for various source positions
Position resolution (RMS):
1.4 cm @ z = 0 cm
1.0 cm @ z = 20 cm
Reconstructed energy [keV]Arbitrary unitDataMC
122
keV
136
keV
59.3 keV (W)
RMS ~4%
XMASS 800kg
Jing LIU @ TAUP2011
22
y [cm]
z [cm]
Data
MC
Arbitrary unitSlide23
Background under control?
ExternalComic ray: underground, muon veto
Ambient gamma & neutron: water shielding
PMT radiation: LXe self-shielding
Internal
Rn
: material screening, clean room filled with Rn free air
Kr: distillation
XMASS 800kgJing LIU @ TAUP201123Slide24
Xe
water
X [cm]
y [cm]
Ambient
and n: pure water tank, ~10 meter
XMASS 800kg
Jing LIU @ TAUP2011
24
Pure water tank (large enough for 26 ton LXe)
equipped with 20 inch PMTs on the wall as
active
muon veto and
passive ambient and n shielding
20 inch PMTs
Water tanks
LXe sphere
10
7
n
eutrons, simulation
g
<<
g
from PMT, n<<10
-4
/d/kgSlide25
LXe copper cryostat
Calibration pipe
g
g
n
n
PMT radiation: Ultra low background PMTs
XMASS 800kg
Jing LIU @ TAUP2011
25
Neutron: <1.2x10
-5
dru
@5-10
keVSlide26
PMT & PMT holder radiation: LXe self-shielding
XMASS 800kg
Jing LIU @ TAUP2011
26
Energy [
keV
]
Counts [
dru
]
Simulation:
g
into
LXe
fiducial
volume: r<20cm, 100 kg LXe
BG/PMT [
mBq
]
U chain
0.70
0.28
Th chain
1.51
0.31
40
K
< 5.10
60
Co
2.92
0.16Slide27
85
Kr (Q
b
=687keV)
: distillation
XMASS 800kg
Jing LIU @ TAUP2011
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Kr
LXe
intake
LXe
outlet
Gas Kr
outlet
K. Abe
et al
. for XMASS
collab
.,
Astropart
. Phys. 31 (2009) 290
Kr can be boiled out from LXe
0.1
ppm
~1ppt (~1 ton in 10 days)Slide28
Kr
concentrationXMASS 800kg
Jing LIU @ TAUP2011
28
Xenon sample
bg
sample 1
bg
sample 2
Kr concentration: < 2.7
ppt
(90% C.L.)Measured by gas chromatography + API mass spectrometerSlide29
222
Rn
XMASS 800kg
Jing LIU @ TAUP2011
29
p0 * exp(-t/
t
) + p1,
t
: decay constant
Time difference
[s]
1st event (
214Bi b)
2nd event (214Po
a)
Tail due tosaturation
214Po decays with 164 ms half life.It can be
identified by time coincidence between two consecutive events:214Bi b
decays into 214Po214Po
a decays into 210Pb
x10
3
Number of photoelectrons
Events
8.2
0.5
mBq
EventsSlide30
220
Rn
XMASS 800kg
Jing LIU @ TAUP2011
30
p0 * exp(-t/
t
) + p1,
t
: decay constant
216
Po decays with 140 ms half lifeTime difference [ms]
EventsEvents
x103
Number of photoelectrons
1
st event
2nd event
<0.28 mBq (90%C.L.)Slide31
Target sensitivity of WIMP-nucleon XS (spin independent)
XMASS 800kg
Jing LIU @ TAUP2011
31
XENON100
CDMSII
XMASS 1yr
Expected energy
spectrum a
ssuming
1 year exposure
flat background (10
-4
dru)
sc = 10
-44 cm
2
MWIMP = 50
GeV
Leff
= 0.2
Black: signal + background
Red: background (10
-4
dru)Slide32
Conclusion
The XMASS 800kg detector is a single phase LXe scintillation detectorConstruction of the 800kg detector finished last winter
Commissioning runs are on going to confirm the detector performance and low background properties
Energy resolution and vertex resolution were as expected. ~1cm position resolution and ~4% energy resolution for 122
keV
g.
Radon and Kr background are close to the target values.The physics results are on the way
XMASS 800kgJing LIU @ TAUP201132Slide33
XMASS 800kg
Jing LIU @ TAUP2011
33
Thanks!Slide34
PMT
holer
made of OFHC copperSlide35
3 Steps in reconstruction
Step1
Search the map grid where likelihood becomes smallest.
Step2
By linear interpolation, calculate likelihood at finer “interpolated grid” in Cartesian coordinate.
1.5cm interval, 5x5x5 finer grid points are evaluated.
Result
grid
of step1
1.5cm
å
-
=
PMT
pe
G
L
)
(
pe
+1)
)
exp
(
Log(
)
Log(
m
m
Ln likelihood is calculated from the expected
pe
and observed
pe
. Using gamma distribution.
Treatment of saturated PMT, cumulative probability of gamma distribution.
z
x
ySlide36Slide37Slide38Slide39
Integral spectrum
Assumption
1x10^-44 cm^2
100 kg X 1 year exposure
WIMP Mass [GeV]
50
100
1000
No. of Events
26
37
6
25 keVr(5keVee) energy threshold
100kg x 1 yearSlide40Slide41Slide42Slide43Slide44
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Jing LIU @ TAUP2011
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