XMASS 2012 Shanghai Particle Physics and Cosmology Symposium Hiroshi Ogawa (ICRR, Univ. of Tokyo) Sep. 16 th , 2012
XMASS
2012 Shanghai Particle Physics and Cosmology Symposium
Hiroshi Ogawa (ICRR, Univ. of Tokyo)Sep. 16th , 2012
XMASS experiment
Dark matter
Double beta
Solar neutrino
2
pp/7Be chain: n+e n+e
136Xe 136Ba + 2e-
χ+Xe χ+Xe
Multi purpose low-background and low-energy threshold experiment with liquid Xenon
Large photon yield Low threshold Scintillation wavelength (175 nm, detected directly by PMT) High density (~3 g/cm3) Compact detector Large Z (=54) Self-Shielding ~-100 liquid : easy to use.℃ Purification (distillation) No long life radioactive isotope
Liquid Xenon :
Direct Detection Principle
• From the density of dark matter in the galaxy:
• Every liter of space: 10-100 WIMPs,
• moving at 1/1000 the speed of light
• Less than 1 WIMP/week will collide with an atom in 1kg material
WIMPs elastically scatter off nuclei in targets, producing nuclear recoils.
Xe (A=131) is one of the best target.
R0: Event rate F: Form Factorshould be calculated in each nuclei
Maxwellian distribution for DM velocity is assumed.v0:dispersionV :velocity onto target, VE: Earth’s motion around the Sun
Spin independent case:
Larger A is higher event rate
Dark Matter(WIMP)
Deposit Energy
• XMASS : single phase detector – Large volume and simple structure, op
eration. • 1 ton scale xenon detector, 100kg f
or fiducial volume.– Background reduction technique :
• Self shielding • Reconstruction by hit pattern of PM
Ts – High light yields & Large photon cover
age (15 pe/keV)• Low energy threshold (< 5 keVee ~
25 keVNR ) for fiducial volume• Lower energy threshold: 0.3 keV fo
r whole volume– Large Scalability, simple to construct.
Characteristics of XMASS
Self shielding
1ton 10ton
XMASS detector : siteKamLAND
Super-KXMASS(Lab-C)
CANDLES
IPMU Lab1 CLIONEWAGE
Lab2/EGadKamioka Mine
Tokyo
Kamioka Mine
10m
11m
Water tank
Refrigerator
72 20inch PMTs (veto)
Elec. hut
•72 20-inch PMTs are installed to veto cosmic-ray muon (<10-6 for thr-mu, 10-4 for stop-mu).•Water is active shield for muon induced neutron and also passive shield for gamma-ray and neutron from rock/wall.
Structure of XMASS detector• Detector
– Single phase (scintillation only) liquid Xenon detector
– Operated at -100oC and 0.065MPa– 100 kg fid. mass, [835 kg inner mass (0.8 m)]– Pentakis-dodecahedron
12 pentagonal with 5 triangle– 630 hexagonal & 12 round PMTs with 28-39%
Q.E.– photocathode coverage: > 62% inner surface
1.2m diameter
Detector construction 2010 Detector construction 2010 11stst application of WC tank for application of WC tank for WIMP search WIMP search
By fall, 2010
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• Calibration– Source Rod (57Co, 241Am, 137
Cs, 109Cd, 55Fe)– External sources: 60Co, 137Cs,
232Th, Neutron• Normal Data taking (physics runs)• Change of the physical condition of
Xenon.– High/Low pressure run
• Change of the refractive index of Xe
– O2 runs: change of the absorption length
– Boiling runs: create convection inside of the detector
• PMT gain reduced run • Evaluate the signal from
radon daughter in xenon.
• Gas run- Important to identify the
surface BG• BG measurement of the
detector parts( attach the material at the end of the calibration source rod) Al, GORE-TEX, Cu, Ni
plate
Data taking :commissioning run Nov.2010-June.2012
Detector response for a point-like source (~WIMPs)
• 57Co source @ center gives a typical response of the detector.
• 14.7p.e./keVee ( 2.2 for S1 in XENON100)
• The pe dist. well as vertex dist. were reproduced by a simulation well.
• Signals would be <150p.e. exp shape.
total photo electron
dataMC
122keV
136keV59.3keV of W
~4% rms
data MC
reconstructed vertex+15V
RI source with rod
RI in PMTActivity per 1PMT(mBq/PMT)
238U-chain 0.70+/-0.28
232Th-chain 1.51+/-0.31
40K-chain 9.10+/-2.15
60Co-chain 4.09+/-0.22
~20
0keV
Energy spectrum data and PMT MC~1
MeV
~50k
eV
MC: PMT rays
Observed data
~x100
Measured Spectrum (Whole Volume) and background evaluation
Gamma from PMTs
RI of PMT are measured by HPGe detector per PMT parts.(+40% for 60Co)Data has large excess in <200keV compared with data. ~x100 difference in ~5keV
Gamma from PMTs had been assumed as mainly background sources
~1M
eV
~50
keV
MC: PMT rays
MC: PMT Al238U & Pb210Surface 210Pb
Observed data
~1M
eV
Measured Spectrum (Whole Volume) and background evaluation
Aluminum Seal
RI from PMT aluminum seal
–Aluminum sealing used for the PMT between quarts window and metal body. It contains 238U-230Th and 210Pb-206Pb.
210Pb on detector surface
222Rn daughter put btw. construction work
These background are faced to liquid xenon.X-ray and beta from RI emit to Liquid xenon directly.
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• GORE-TEX: between PMT and holder used for a light seal. It contains 06±3% of modern carbon.
– GORE-TEX might explain the background below 5keV
• But parameters ( ex. transparency of light inside of GORE-TEX) are not well known
• We will remove GORE-TEX in future detector refurbishment
Measured Spectrum (Whole Volume) and background evaluationBelow 5keV
14C in GORE-TEXMC: GORE-TEXModern C: 7.5%LXe inside scintillate0.3mm photon att.
~5ke
V
MC: GORE-TEXModern C: 7.5%LXe inside scintillate0.1mm photon att.
~5ke
V
mDM = 30GeVSI = 1.4x10-41cm2
Background estimates
Material Measured RI and activity Methods of the measurements
PMTs
(per PMT)
238U: 0.704 ± 0.282 mBq
232Th: 1.51 ± 0.31 mBq
60Co: 2.92 ± 0.16 mBq
40K: 9.10 ± 2.15 mBq
HPGe detector measurement for each parts and whole PMT
PMT aluminum
(210g)
238U-230Th: 1.5 ± 0.4 Bq
210Pb: 5.6 ± 2.3 Bq
232Th: 96 ± 18 mBq
235U: ~67 mBq
HPGe detector measurement.
By calculation
Detector surface 210Pb: ~40 mBq
Alpha candidates using FADC data
Surface: PMT window 59%, PMT Al 7.0% PMT rim 7.0%, GORETEX 3.7%, Cu 23.3% (surface 7.8%, wall 14.2%, bottom 1.3%)
GORE-TEX for PMTs
(120g)
14C: 0.4 ± 0.2 Bq
(6±3% of modern carbon)
210Pb: 26.5 ± 11.9 mBq
14C: modern carbon measurement.
210Pb: Ge measurement.
Internal RI in xenon
85Kr: <2.7 ppt
214Pb: 8.2 mBq
85Kr : API-MS measurement
214Pb : ~222Rn concentration in detector
Low background even with the surface BG
• Our BG is still quite low, even with the extra surface BG!• In principle, the surface BG can be eliminated by vertex
reconstruction. Optimization of the reconstruction program is on going to minimize a possible leakage to the inner volume.
E. Aprile, 2010 Princeton
XMASS full volume
• Our sensitivity for the low mass WIMP signals at low energy without reconstruction will be shown. Ev
ens/
kg/d
ay/k
eV
16
Physics analysis(sensitivity study)
•Whole Volume Analysis (Large BG, Large target mass of 835 kg, low energy threshold, no reconstruction)
1) 4 hit threshold analysis• Low mass region search
2) 1keVee threshold analysis• Check DAMA modulation
3) Axion DM (super-WIMPs)4) Solar Axions
•Fiducial Volume analysis1) Standard WIMPs search (> 5 keV)
• Event reconstruction/reduction Standard WIMPs:Prefer heavy massLow BG
Light WIMPs & ALP:Low thresholdBG less important
Physics analysis:Physics analysis:Low energy, full volume analysis for low mass WIMPsLow energy, full volume analysis for low mass WIMPs• The dark matter signal rapidly incre
ase toward low energy end. The large p.e. yield enables us to see light WIMPs. Try to set absolute maxima of the cross section (predicted spectrum must not exceed the observed spectrum).
• The largest BG at the low energy end is the Cherekov emission from 40K in the PMT photo cathodes.
Light WIMPs & ALP:Low thresholdBG less important
Selection criteria for data: Triggered by the inner detector only (no water tank trigger)RMS of hit timing <100ns (rejection of after pulses of PMTs)Cherenkov rejectionTime difference to the previous/next event >10ms
Detail of the Cherenkov rejectionDetail of the Cherenkov rejection• Basically, separation between
scintillation lights and Cherenkov lights can done using timing profile.
• (# of hits in 20ns window) / (total # of hits) = “head total ratio” is a good parameter for the separation. Total # of hits Total # of hits
20ns 20ns
Cherenkov like Scintillation like
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• Cherenkov events peaks around 1 scintillation ~ 0.5• Low energy events observed in Fe55 calibration source as well as DM simul
ation (t=25ns) show similar distributions.• Efficiency ranges from 40% to 70% depending on the p.e. range.
0 40 80 120 160 2000 40 80 120 160 200
(PE)(PE)
Head t
ota
l ra
tio
Head t
ota
l ra
tio
Black: real data Black: real data
Blue: DM MC
p.e. distribution after each cutp.e. distribution after each cut• 6.8 days x 835kg data• The Cherenkov events are efficiently reduced by the cut.
• We analyze the events above > 0.3 keVee for entire volume
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ID only event (trigger ID == 1)dT > 10msRMS of hit timing < 100nsCherenkov cut
Uncertainties• Major uncertainty is the scintillation efficiency of nuclear r
ecoil in liquid xenon.• Uncertainties of the trigger thre. (hard trig. 4hits), cut eff.,
and energy scale are also properly taken into account.
Scintillation efficiency as a function of energyE. Aprile et al., PRL 105, 131302 (2010)
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Spectrum and Sensitivity Spectrum and Sensitivity • Spectrum shows that observed data and MC WIMPs signal with best fit per WIMPs mass. • Sensitive to the allowed region of DAMA/CoGeNT. • Some part of the allowed regions can be excluded.
DAMA
CoGeNTXMASS
23
WIM
P c
ross
sect
ion
on
nu
cleon
(cm
2)
XMASS observed energy [keVee]
Cou
nt/d
ay/k
g/ke
Vee
GeV
Preliminary
Preliminary
Progress of annual modulation analysis
1-4 keVee(Xe) 2-6 keVee (Na)
• Check the DAMA modulation• QF(Na)0.25, Leff(Xe)0.15• 26keVee(Na) 824 keVNR 14keVe
e(Xe)– but 1/30 sensitivity recoil shape, A2
2: 10.8 for flat, 23.8 for a modulation
Preliminary
Preliminary
2013 data taking (after refurbishment) will cover the maximum and minimum flux region.
Dark matter axion search in XMASSDark matter axion search in XMASS• The DAMA signal may be due to electromagnetic interac
tion of WIMPs to the NaI detectors by such as a non-relativistic axion dark matter. See J. Collar, arXiv: 0903.5068
• XMASS can search for dark matter axion by detection through axio-electric effect.
• We show a preliminary result based on 6.8 days x 835kg data.
gaee
Limit on the axio-electric couplingLimit on the axio-electric coupling
DAMA allowedCoGeNTCDMSXMASS
gaee
Sensitivity withspectrum fittingwith background MC
Preliminary
Preliminary
(keVee)
Observed spectrumExpectation for ma=3keV
Even
ts/k
eV/k
g/da
y
We obtained a limit on the axio-electric coupling (gaee) by comparing the observed spectrum and the expectation.
The result can be further improved above 5keV by fitting spectrum.
Solar axion search in XMASSSolar axion search in XMASS
Observed spectrumMC axion signalsAbs upper limit gaee=4.5e-11
XMASS can also search for solar axion emitted owing to Bremsstrahlung and Compton processes in the Sun, by detection through axio-electric effect. We obtained a limit on axio-electric coupling (gaee)
Solar axion flux (Derbin et al., arXiv:1206.4142)
gaee=10-10
Allowed mass< 200eV for KSVZ<2eV for DFSZ
Originalfigure fromDerbin et al., 1206.4142
XMASSLimit by DM
XMASSLimit by solar axion4.5e-11
Solar limit2.8e-11
Limits on gLimits on gaeeaee from XMASS (DM+solar) from XMASS (DM+solar)
Preliminary
Preliminary
Plan: Refurbishment work
• Tuning of reconstruction/reduction is on going but for better sensitivity, removing the origins of BG must be done.
• To reduce the BG caused by Aluminum, we are planning to cover the part and surfaces by copper rings and plates:
• BG > 5keV must be reduced significantly (1/100 of current BG).• Schedule: start physics run from 2013
Expected sensitivity with fiducialization
XENON100CDMSII
XMASS 2keVee thre. 100d
Black:signal+BGRed:BG
Expected energy spec.
1 year exposurep=10-44 cm2
50GeV WIMP
Spin Independent
XMASS 5keVee thre. 100d
Initial target of the energythreshold was ~5keVee.Because we have factor ~3better photoelectron yield,lower threshold = smaller massdark matter may be looked for.
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XMASS1.5 (2015-)• Total mass: 5 tons• Fiducial mass: 1 ton 10
0kg• Backgrounds
– No dirty aluminum– No GORETEX– Less surface 210Pb
• New PMTs.• Expect 10-5 dru• Sensitivity sSI < 10-46 cm2 (> 5 ke
V)• Low threshold analysis could rea
ch a few x 10-42 cm2 around a few GeV region.
XENON100
CDMSIIEDELWEISSII
DAMA
CoGeNT
SummarySummary• The XMASS 800kg detector was constructed and started co
mmissioning late 2010.• We completed commissioning data-taking and physics anal
yses are on-going.• BG level is not as low as originally expected, but now the c
omposition is well understood above 5keV.• Some preliminary results on dark matter and axion searche
s are shown. More results will come later.• By improving software (reconstruction/BG reduction) and ha
rdware refurbishment, we aim at the dark matter search with the original sensitivity.
• And XMASS1.5 will progress. Physics run is planed from 2015.
XMASS collaborationICRR, University of Tokyo K. Abe, K. Hieda, K. Hiraide, Y. Kishimoto, K. Kobayashi, Y. Koshio,
S. Moriyama, M. Nakahata, H. Ogawa, H. Sekiya, A. Shinozaki, Y. Suzuki, O. Takachio, A. Takeda, D. Umemoto, M. Yamashita, B. Yang
IPMU, University of Tokyo J. Liu, K. Martens
Kobe University K. Hosokawa, K. Miuchi, A. Murata, Y. Ohnishi, Y. Takeuchi
Tokai University F. Kusaba, K. Nishijima
Gifu University S. Tasaka
Yokohama National University
K. Fujii, I. Murayama, S. Nakamura
Miyagi University of Education
Y. Fukuda
STEL, Nagoya University Y. Itow, K. Masuda, H. Takiya, H. Uchida
Kobe University K. Ohtsuka, Y. Takeuchi
Seoul National University S. B. Kim
Sejong University N.Y. Kim, Y. D. Kim
KRISS Y. H. Kim, M. K. Lee, K. B. Lee, J. S. Lee
Cryogenic
700LLiq.
Storage
liquid pump
Condenser360W
gas pump
filtersCalibration line
Cable line
filters
Outer vacuum
857kg
10 m3 x 2
gas storage
emergency gas pump
100L/min
evaporator
Water tank
Liquid circulation ~5L/min
Gas circulation <30L/minXMASS Xenon
operating system
Xenon keeping : Pulse tube refrigerator.Xenon circulation : Gas phase: < 30 L/minLiquid phase: ~ 5 L/minXenon collection :700L liquid storage tank.10m3 x 2 gas storage tank.
We successed the xenon filling/collection for 5 times with keeping the amount and quality of xenon.
Internal RI in xenon
100 500 1000Time difference (s)
Fitting withan expecteddecay curve
1st event (214Bi )2nd event (214Po )
222Rn 220RnRadon concentration: 222Rn : 8.2+/-0.5mBq220Rn : <280microBq (90%C.L.)
220Rn candidate216Po candidate ~accidental
164us 145ms※214Pb, 212Pb(daugther of radon) is source of background in low energy. These background is remained even after fiducial volume cut. 8.2mBq ~ 2x10-4dru contribution.