Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Recent status of the XMASS projectRecent status of the XMASS project
Physics goals at XMASS Overview of XMASS Current status of R&D Summary
Yasuo Takeuchi(Kamioka Observatory, ICRR, Univ. of Tokyo) for XMASS Collaboration
XMASS = a multi purpose detector to search rare phenomena under an ultra low background environment by using ultra pure liquid xenon
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Physics goals at XMASSPhysics goals at XMASS
Xenon MASSive Detector for Solar Neutrinos (pp/7Be) Xenon Detector for Weakly Interacting MASSive
Particles (Dark Matter Search) Xenon Neutrino MASS Detector (Double Beta Decay)
XMASS FV 50 ton year(90%CL)
G. Gratta@Neutrino2004
http://www.sns.ias.edu/~jnb/pp+-1%
Measure pp via + e + e
2 life time should be measuredIsotope separation would be needed
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Expected signal
Physics goals at XMASSPhysics goals at XMASS
Xenon MASSive Detector for Solar Neutrinos (pp/7Be) Xenon Detector for Weakly Interacting MASSive
Particles (Dark Matter Search) Xenon Neutrino MASS Detector (Double Beta Decay)
Direct search via nuclear elastic scattering
XMASS FV 0.5ton yearEth=5keV, 3 discovery
Eth = 5keV ~200 events/day/ton
Eth = 20keV ~3 events/day/ton
Spin Independent
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Xenon MASSive Detector for Solar Neutrinos (pp/7Be) Xenon Detector for Weakly Interacting MASSive
Particles (Dark Matter Search) Xenon Neutrino MASS Detector (Double Beta Decay)
Physics goals at XMASSPhysics goals at XMASS Search for 0 (2) decay of
136Xe (na 8.87%) High purity and enriched Xe can
be used. Energy region is different from
solar / DM. PMTs should not be placed near
the detector.
Need another design of the detector!(low priority, at moment…)
136Xe 136Ba + e- + e-
Q-Value: 2.48 MeV
2 1/2 theory=8 x 1021 y
Overview of XMASSOverview of XMASS
Strategy
Key ideas (self shielding, distillation)
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Strategy of the XMASS projectStrategy of the XMASS project
Dedicated detector forDouble beta decay search
~1 ton detector(FV 100kg)Dark matter search
~20 ton detector(FV 10ton)Solar neutrinosDark matter search
Prototype detector (FV 3kg) R&D
~2.5m~1m~30cm
NOW
Confirmation of feasibilities of the ~1 ton detectorAnalysis techniquesSelf shielding performanceLow background propertiesPurification techniques
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Self shieldingSelf shielding
PMTs
Liquid Xe Volume for shielding
Fiducial volume
Quite effective for the events below ~500 keV (pp & DM) Not effective for double beta decay experiment
Reconstruct the vertex and energy based on PMTs information (light pattern)
30cm 105 reduction for < ~500keV
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Distillation to remove KrDistillation to remove Kr Very effective to eliminate internal impurities
(85Kr, etc.) We have processed 100kg Xe in March ‘04
Boiling point
(@1 atm)
Xe 165K
Kr 120K
~3m
13 stage of Operation: 2 atmProcessing speed: 0.6 kg / hourDesign factor: 1/1000 Kr / 1 pass
Lower temp.
Higher temp.
~1%
2cm
~99%Purified Xe: < 5 ppt Kr (measured)
Off gas Xe:330±100 ppb Kr(measured)
Raw Xe: ~3 ppb Kr
Current status of Current status of R&DR&D
Prototype detectorResults from test runs
Self shieldingInternal background External background
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
XMASS prototype detectorXMASS prototype detector 30 litter liquid Xenon (~100kg) Oxygen free copper: (31cm)3
54 of low-BG 2-inch PMT Photo coverage ~16%
MgF2 window 0.6 p.e. / keV
Polyethylene (15cm)
Boric acid (5cm)Lead (15cm)EVOH sheets (30mm)OFC (5cm)Rn free air (~3mBq/m3)
1.0m
1.9m
n
Rn
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Test runs with the prototype detectorTest runs with the prototype detector December 2003 run
First test run ~6 days (~2day normal runs for BG estimation) Test analysis tools Confirmation of the self shielding performance Measurements of the internal and external BGs
August 2004 run August 3 ~ 11, 2004, 9days (~6day normal runs) Used purified xenon (by distillation) Longer baking time of the system New electronics (TDC, etc.) Re-measurements of the internal and external BGs
NEW
Photon yield x ~1.7
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
DataMC
DataMC
Z= +15Z= -15
Remove events (PMT saturation)
60Co (1173 & 1333keV)137Cs (662keV)
Self shielding performanceSelf shielding performanceReconstructed vertex position of collimated source runs
Dec.03 run
MC reproduces data very well We have demonstrated the self-shield actually works
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Internal BG source: Internal BG source: 222222RnRn
2 separate runs to check 222Rn decay (1/2=3.8day)
4th Aug. 0.8day 238U=(72+-11)x10-14 g/g 10th Aug. 1.0day 238U=(33+-7)x10-14 g/g
Consistent with expected 222Rn decay
((30+-5)x10-14 )
Aug.04 runPreliminary
T: 1/2 = 141+-51sec
T < 1ms
(1.8days)
3.5MeV
67ev
214Bi 214Po 210Pb
1/2 =164sec
(Emax=3.3MeV) (7.7MeV)
238U
222Rn
L
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Internal background sourcesInternal background sources
Current results238U: = (33+-7)x10-14 g/g
232Th: < 63x10-14 g/g
Kr: < 5ppt
Goal (~1ton)
1x10-14 g/g
Factor <~30 (under further study)
Almost achieved by the distillation process
2x10-14 g/g
1 ppt
Factor ~30, but may decay out further
Preliminary
NEW
NEW
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
[co
un
t/ke
V/d
ay/k
g]
(=d
ru)
External background sourcesExternal background sources Background level was estimated from known
sources
MC estimation for full volume rays from outside shield
PMTs origin 238U series 40K 232Th series
210Pb in the lead shield
Energy (keV)
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Measured background levelMeasured background level
Self shielding works Good agreement with expectation (< factor 2)
MeasurementsAll volume20cm FV10cm FV
SimulationAll volume20cm FV10cm FV
Aug.04 runPreliminary
Geometrical effect only for prototype detector
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Alpha vs Gamma separationAlpha vs Gamma separationAug.04 runPreliminary
Alpha-gamma separation by using FADC wave form would be possible (under further investigation)
Pulse width (ns)
Cha
rge
Alpha-like Gamma-like
FADC data
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
SummarySummary XMASS is aiming to search rare phenomena under an ultra
low background environment by using ultra pure liquid xenon.
2nd test run with the prototype detector was just finished. The data were taken using distilled xenon with low level
krypton (Kr/Xe < 5ppt). Some part of remaining 222Rn in liquid xenon looks
contaminated in outside of the chamber. The background level is consistent with expectation
within factor about 2. The next step (~1ton scale) would be feasible, and a dark
matter search around 10-44 cm2 level would be possible.
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Supplement
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Why liquid xenon scintillatorWhy liquid xenon scintillator High photon yield
Low threshold, good energy resolution, …
Can be directory read by PMT Large atomic number
Radiation length ~2.4cm Self shielding against external
backgrounds Compact (R=1.22m for 23 tons)
Easy to liquefy Liquid N2 can be used
Various purification method Distillation, circulation during
experiment, … Effective reduction against internal
backgrounds No long life radioactive isotopes 136Xe is a decay candidate
Scintillation light ~42photon/keV
Scintillation light wave length
175nm
Scintillation light width
~40nsec
Atomic number 54
Atomic weight 131.29 amu
Density 3.0 g/cm3
Melting (boiling) point
161.4K (165.1K)
Chemical series Noble gases
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
U 1.5±0.3x10-3 Bq Th 3.2±4.6x10-4 Bq40K 1.7±2.9x10-3 Bq
Development of the low BG PMTDevelopment of the low BG PMT
Aiming for another order of magnitudes improvementHexagonal PMTto accomplish 70-80% PMT coverage
Q.E. ~ 30% @ 175nm; Collection eff. ~ 90%Quartz window & Metal tube (Low BG)Selection of the parts ( measured by HPGe ) Low BG PMT base ~1/10 of the usual ones
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Energy/vertex reconstructionEnergy/vertex reconstruction
137Cs 662keV Gamma ray ( from a collimator)
F(x,y,z,i): hitmap made by MCVUV photon characteristics:
Lemit=42ph/keVabs=34cm scat=30cm
Reconstructedhere
PMT
n
nL )
!
)exp(Log()Log(
L: likelihood: F(x,y,z,i)/ F(x,y,z,j)
x(total p.e.)n: observed number of p.e.
.
Real data
j
Using photoelectron map made by MC (not timing, but charge information)
Vertex: MC hitmapEnergy: Hitmap scale
Dec.03 run
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Event reconstructionEvent reconstruction
ABC+++
Collimated gamma rays for three different positions
Hole AHole BHole C
Real data
MC
Reconstruction works well
137Cs
Dec.03 run
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Stability of the energy scaleStability of the energy scaleAug.04 runPreliminary
No degrading of the energy scale Stable within +-0.5%
60Co calibration data
Peak position from simple gaussian fit+-0.5%
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Observed light yieldObserved light yield
Observed number of photons for source runs are increased by factor ~1.7 xenon purification longer baking time removal of
unnecessary material in the chamber
Aug.04 runPreliminary
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
8585Kr: 687keV beta analysisKr: 687keV beta analysis
The event rate around 200~400 keV in the Normal runs could be explained by 2~3ppb of Kr.
Dec.03 run
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Measured background levelMeasured background level
Excess in 200-400keV in Dec. 2003 run may be due to 85Kr
Simulation
Aug.04 runPreliminary
Dec. 2003 run Aug. 2004 runAll volume20cm FV10cm FV
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
232232Th seriesTh series
212Bi 212Po 208Pb
1/2 =299nsec
(Emax=2.3MeV) (8.8MeV)
-tagged beta events of 212Bi and 212Po High- and Middle-gain normal runs: 1.66day 20cm fiducial volume cut (to reject external events)
1st peak: < 2000p.e. (efficiency ~100%) T=160~6000nsec in Flash ADC (efficiency = 69%)
2nd peak: 500 ~ 4500p.e. (efficiency ~100%)
(BR=64%)
1 event remained
Dec.03 run
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Typical FADC data & peak searchTypical FADC data & peak search
54 PMT analog sum 1 FADC
Range: -8 ~ +8sec 80~240nsec window
Threshold: 70 count (4~12p.e.)
Most of peaks
= after pulses from PMTnsec
FADC count
Peak position
Pedestal(80nsec)
Trigger timing
Dec.03 run
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
232232Th series: Bi-Po analysis (FADC)Th series: Bi-Po analysis (FADC)
1 candidate event 232Th < 63x10-14 g(232Th)/g(Xe) (90%CL)
Trigger timing
1st peak 2nd peak (T~700nsec)
nsec
FA
DC
co
un
t
Keep this eventconservatively,for now
(only stat. error)
(OK) (very high energy?)
Dec.03 run
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
An idea of dedicated detector forAn idea of dedicated detector for
Put room temperature LXe intoa thick, acrylic pressure vessel (~50atm).
Wavelength shifter inside the vessel.
We already have 10kg enriched 136Xe.
Test vessel held 80 atm water
(symbolically)
Y.Takeuchi @ICHEP04 in BeijingAugust 18, 2004
Expected sensitivityExpected sensitivity Assume acrylic material U,Th~10-12g/g, no other BG. Cylindrical geom. (4cm dia. LXe, 10cm dia. Vessel) 10kg 136Xe 42000photon/MeV but 50% scintillation yield, 90% eff.
shifter, 80% water transparency, 20% PMT coverage, 25% QE 57keVrms @ Q=2.48MeV
1yr, 10kg measurement 1.5 x 1025 yr <m>=0.2~0.3eV
If U/Th ~ 10-16 g/g + larger mass <m>~0.02-0.03eV2 will not be BG thanks to high resolution
U+Th normalized for 10kg, 1yr