the xmass 800kg experiment jing liu ipmu, univ. of tokyo taup2011, munich xmass collaboration:...
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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.LiuKobe University: Y. Takeuchi, K. Otsuka, K. Hosokawa, A. MurataTokai University: K. Nishijima, D. Motoki, F. KusabaGifu University : S. TasakaYokohama National University : S. Nakamura, I. Murayama, K. FujiiMiyagi University of Education : Y. FukudaSTEL, Nagoya University : Y. Itow, K. Masuda, H. Uchida, Y. Nishitani, H. TakiyaSejong University : Y.D. KimKRISS: Y.H. Kim, M.K. Lee, K. B. Lee, J.S. Lee
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The XMASS Experiment
XMASS 800kg Jing LIU @ TAUP2011 2
Xenon MASSive detector for Solar neutrino (pp/7Be)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
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Jing LIU @ TAUP2011
The XMASS Experiment
XMASS 800kg 3
Xenon MASSive detector for Solar neutrino (pp/7Be)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
scintillation
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Jing LIU @ TAUP2011
The XMASS Experiment
XMASS 800kg 4
Xenon MASSive detector for Solar neutrino (pp/7Be)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
LXe
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The XMASS Experiment
XMASS 800kg Jing LIU @ TAUP2011 5
Xenon MASSive detector for Solar neutrino (pp/7Be)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
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Jing LIU @ TAUP2011
The XMASS Experiment
XMASS 800kg 6
Xenon MASSive detector for Solar neutrino (pp/7Be)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
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Jing LIU @ TAUP2011
The XMASS Experiment
XMASS 800kg 7
Xenon MASSive detector for Solar neutrino (pp/7Be)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
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Jing LIU @ TAUP2011 8
Structure of XMASS 800kg detector
XMASS 800kg
PMT
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Jing LIU @ TAUP2011 9
Structure of XMASS 800kg detector
XMASS 800kg
PMT
Pentakis dodecahedron
~10 PMTs in one triangle642 PMTs in total
~0.8 meter
PMT photo-cathodes cover ~62% inner surface
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Jing LIU @ TAUP2011 10
Reconstruct interaction point from PMT hit pattern
XMASS 800kg
Colored photo cathodes indicating number of p.e. (photoelectrons) recorded by PMTs
Interaction point (vertex) can be reconstructed from the PMT hit pattern.
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Jing LIU @ TAUP2011 11
LXe self-shielding
XMASS 800kg
Simulation: g into LXe
waterLXe
E [keV]
Att
enu
atio
n le
ng
th o
f
[cm
]
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Jing LIU @ TAUP2011 12
Where is it?
XMASS 800kg
1000 m rock overburden(2700 m water equiv.):Muon: 6.0x10-8 /cm-2/s/srNeutron: 1.2x10-6/cm-2/s
360m above the sea
Horizontal access:15 minutes drive from office,too easy to get in!No excuse to avoid 24-hour shift
Kamioka underground observatory
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Jing LIU @ TAUP2011 13XMASS 800kg
New experimental hall, Aug. 2008
15 meter15
met
er20 meter
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Jing LIU @ TAUP2011 14XMASS 800kg
water tank, Nov. 2008
10 m x 10 m
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Jing LIU @ TAUP2011 15XMASS 800kg
Frame of clean room in water tank, Mar. 2008
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Jing LIU @ TAUP2011 16XMASS 800kg
PMT mounting in clean room, Dec. 2009
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Jing LIU @ TAUP2011 17XMASS 800kg
PMT mounting finished, Feb. 2010
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Jing LIU @ TAUP2011 18XMASS 800kg
Water filling, Sep. 2010
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Jing LIU @ TAUP2011 19XMASS 800kg
Commissioning started, Nov. 2010
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Scintillation light yield :: calibration system
XMASS 800kg
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
57Co, 241Am, 109Cd, 55Fe, 137Cs
~F 4mm
~F 0.15mm for 57Co
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Scintillation light yield: 15.9 1.2 p.e./keV (57Co at center)
XMASS 800kg
DataMC
122 keV
136 keV59.3 keV (W)
Number of photoelectrons
Arbi
trar
y un
it
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Position & energy resolution (122keV g from 57Co)
DataReconstructed vertices for various source positions Position resolution (RMS):
• 1.4 cm @ z = 0 cm• 1.0 cm @ z = 20 cm
Reconstructed energy [keV]
Arbi
trar
y un
it
DataMC
122 keV
136 keV59.3 keV (W)
RMS ~4%
XMASS 800kg Jing LIU @ TAUP2011 22
y [cm]
z [cm]
DataMC
Arbi
trar
y un
it
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Jing LIU @ TAUP2011 23
Background under control?
• External– Comic 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 800kg
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Jing LIU @ TAUP2011 24
Xe
water
X [cm]y
[cm
]
Ambient and n: pure water tank, ~10 meter
XMASS 800kg
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
Wat
er ta
nks
LXe sphere
107 neutrons, simulation
g << g from PMT, n<<10-4/d/kg
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Jing LIU @ TAUP2011 25
LXe
copp
er c
ryos
tat
Calib
ratio
n pi
pe
g
g n
n
PMT radiation: Ultra low background PMTs
XMASS 800kg
Neutron: <1.2x10-5 dru @5-10 keV
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Jing LIU @ TAUP2011 26
PMT & PMT holder radiation: LXe self-shielding
XMASS 800kg
Energy [keV]C
oun
ts [
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 0.3140K < 5.1060Co 2.92 0.16
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85Kr (Qb=687keV) : distillation
XMASS 800kg
Kr
LXeintake
LXeoutlet
Gas Kroutlet
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)
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Kr concentration
XMASS 800kg
Xenon samplebg sample 1bg sample 2Kr concentration: < 2.7 ppt (90% C.L.)
Measured by gas chromatography + API mass spectrometer
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Jing LIU @ TAUP2011 29
222Rn
XMASS 800kg
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:
1. 214Bi b decays into 214Po2. 214Po a decays into 210Pb
x103
Number of photoelectrons
Even
ts
8.20.5 mBq
Even
ts
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Jing LIU @ TAUP2011 30
220Rn
XMASS 800kg
p0 * exp(-t/t) + p1,t: decay constant
216Po decays with 140 ms half life
Time difference [ms]
Even
ts
Even
ts
x103
Number of photoelectrons
1st event2nd event
<0.28 mBq (90%C.L.)
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Jing LIU @ TAUP2011 31
Target sensitivity of WIMP-nucleon XS (spin independent)
XMASS 800kg
XENON100
CDMSII
XMASS 1yr
Expected energy spectrum assuming
• 1 year exposure• flat background (10-4 dru)• s c = 10-44 cm2
• MWIMP = 50 GeV
• Leff = 0.2
Black: signal + backgroundRed: background (10-4dru)
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Conclusion
• The XMASS 800kg detector is a single phase LXe scintillation detector
• Construction 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 800kg
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Jing LIU @ TAUP2011 33XMASS 800kg
Thanks!
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PMT holer made of
OFHC copper
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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
GL )
(pe+1)
)exp(Log()Log(
mm
• 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
y
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Integral spectrum
Assumption 1x10^-44 cm^2100 kg X 1 year exposure
WIMP Mass [GeV]
50 100 1000
No. of Events 26 37 6
25 keVr(5keVee) energy threshold100kg x 1 year
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Jing LIU @ TAUP2011 44XMASS 800kg
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Jing LIU @ TAUP2011 45XMASS 800kg
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Jing LIU @ TAUP2011 47XMASS 800kg