the xmass 800kg experiment jing liu ipmu, univ. of tokyo taup2011, munich xmass collaboration:...

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

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

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

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

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

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

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

Jing LIU @ TAUP2011 8

Structure of XMASS 800kg detector

XMASS 800kg

PMT

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

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.

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

]

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

Jing LIU @ TAUP2011 13XMASS 800kg

New experimental hall, Aug. 2008

15 meter15

met

er20 meter

Jing LIU @ TAUP2011 14XMASS 800kg

water tank, Nov. 2008

10 m x 10 m

Jing LIU @ TAUP2011 15XMASS 800kg

Frame of clean room in water tank, Mar. 2008

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PMT mounting in clean room, Dec. 2009

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PMT mounting finished, Feb. 2010

Jing LIU @ TAUP2011 18XMASS 800kg

Water filling, Sep. 2010

Jing LIU @ TAUP2011 19XMASS 800kg

Commissioning started, Nov. 2010

Jing LIU @ TAUP2011 20

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

Jing LIU @ TAUP2011 21

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

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

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

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

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

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

Jing LIU @ TAUP2011 27

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)

Jing LIU @ TAUP2011 28

Kr concentration

XMASS 800kg

Xenon samplebg sample 1bg sample 2Kr concentration: < 2.7 ppt (90% C.L.)

Measured by gas chromatography + API mass spectrometer

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

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.)

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)

Jing LIU @ TAUP2011 32

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

Jing LIU @ TAUP2011 33XMASS 800kg

Thanks!

PMT holer made of

OFHC copper

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

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

Jing LIU @ TAUP2011 44XMASS 800kg

Jing LIU @ TAUP2011 45XMASS 800kg

Jing LIU @ TAUP2011 46XMASS 800kg

Jing LIU @ TAUP2011 47XMASS 800kg