xmass
DESCRIPTION
LowNu 2003, May 20. XMASS. Kamioka observatory, ICRR, Univ. of Tokyo M. Nakahata for XMASS collaboration. ・ Physics motivation of XMASS ・ R&D using 100kg detector ・ Next step: 800 kg detector. XMASS collaboration. ICRR, Kamioka observatory - PowerPoint PPT PresentationTRANSCRIPT
XMASS
・ Physics motivation of XMASS
・ R&D using 100kg detector
・ Next step: 800 kg detector
Kamioka observatory, ICRR, Univ. of Tokyo
M. Nakahata
for XMASS collaboration
LowNu 2003, May 20
XMASS collaboration• ICRR, Kamioka observatory Y. Suzuki, M. Nakahata, Y. Itow, M. Shiozawa, Y. Takeuchi, S. Moriyama, T. Namba, M. Miura,Y. Koshio, Y. Fukuda, S. Fukuda, Y. Ashie, A. Minamino, R. Nambu• ICRR, RCNNT. Kajita, K. Kaneyuki, A. Okada, M. Ishitsuka• Saga Univ.T. Tsukamoto*, H. Ohsumi, Y. Iimori, • Niigata Univ.K. Miyano, K. Ito• Tokai Univ.K. Nishijima, T. Hashimoto, Y. Nakajima• Gifu Univ.S. Tasaka,• Waseda Univ.M. Yamashita, S. Suzuki, K. Kawasaki, J. Kikuchi, T. Doke,• TITY. Watanabe, K. Ishino, • Yokohama National Univ.S. Nakamura, T.Fukuda, J.Hosaka, • Seoul National Univ.Soo-Bong Kim, In-Seok Kang,• INR-KievY. Zdesenko, O. Ponkratenko,• UCIH. Sobel, M. Smy, M. Vagins, P.Cravens
XMASS
Scintillation detection by PMTs
Dark M: Xenon detector for weakly interacting MASSive Particles : Xenon neutrino MASS detectorSolar : Xenon MASsive detector for Solar neutrinos
10 ton class Liq. Xe
Dark matter search
Eth = 20keV; 30 events/dayEth = 5keV; 2000 events/day
Expected signal of dark matter
Sensitivity of dark matter search 10 ton Liq. Xe
Spin independent
Spectrum only
Seasonal variation
10-6 pb
Double deta decay
e-
e-
e-
e-
Majorana mass of neutrinos
It is quite important to investigate whether the origin of the neutrino mass is Majorana type
See-saw mechanism is correct ?
136Xe(natural abundance 8.87%), double beta nuclei
22 02
background against
1/2 theory=8 x 1021 y
Resolution by photon statistics
42000potons/MeV x 2.48MeV x 30%Q.E.
31000 p.e. 0.6 % rms
10ton natural, 5 year
2600 keV24002200
Signal region
1/2 theory=8 x 1021 y
background against
Sensitivity of
10ton natural, 5 year
Both +- sigma
Only + sigma
mMajorana sensitivity: 0.01 – 0.02 eV
0 1 2 3 4 5 6Resolution at 2.5 MeV
0 1 2 3 4 5 6Resolution at 2.5 MeV
02 lifetime sensitivity: several ×1027 years
10t Liq. Xe 5yr
(Cf. SK-I, ~13 events/day)
Solar neutrinospp: 10ev/day7Be: 5ev/day (> 50keV, SSM)
Expected spectrum of solar neutrinos
+e + e
~1% stat. error measurement of pp flux
Quite High statistics
KamLAND and pp solar neutrinos will determine precise oscillation parameters
Precise measurement of oscillation parameters
• Expected region using pp neutrinos (90 % C.L.) : 10 ton Liq. Xe e scattering 5 years data Statistical error and SSM pre
diction error(1%) • Accuracy of mixing angle: sin22
= 0.77 0.03(stat.+SSM)
Fiducial volume
rays from 238U chain
Background rejection
6 orders of magnitude reduction for gamma rays below 500keV
(U/Th/K/Co/Cs/…)
neutron
rays from 85
Kr, 42,39Ar, U/Th
Self-shield
No long life isotope
H2O, paraffinDistillation
• Self-shield of external gamma rays
Development of low background PMTs• New type 2-inch PMT(developed with Hamamatsu Co.)
Q.E. ~ 30% @ 175nmCollection efficiency ~ 90%Quartz windowMetal tube (low background)Parts were selected using HPGe
Single p.e. distribution
Bq/PMTequiv.10-3 10-210-4
New 2-inch PMTMetal forPMT bulb
capacitor (film)Chip resistorQuartz (PMT)CablesPCB(PTFE)
Usual PMTs
Resistor
capacitor
Glass Epoxy PCB
Selection of parts for the new type PMT
Low BG PMT 238U 1.8x10-2Bq232Th 6.9x10-3Bq40K 1.4x10-1Bq60Co 5.5x10-3Bq
Bulb for PMT
100kg detectorpurpose
MgF2 window
54 2-inch PMTs
Liq. Xe (30cm)3=30L=100Kg
(1) Low background effort with new PMTs(2) Vertex/energy reconstruction(3) Demonstration of self shielding(4) e/separation(5) R&D of purification system(6) Possible detection of 2 decay
100kg detector
MgF2 window
Supur-insulation
100kg detector: cooling
Vacuum chamber (this time stainless steel)
GM refrigerator ( 100W @170K )
Cooling and liq.Xe supply, recovery test in February using only 6 PMTs
100kg detector cooling
PMT mouting
One PMT per plane
Temperature monitor
PMTPMT HV ON
8 days
detector
Supply liq. Xe
100kg detector: Gas line
Getter
Original Xe
Recovery Xe
Emergency tank(9m3)
Vacuum chamber
Emergency recovery line
rupture disk
Emergency valve
Liq. N2
Level Monitor
4 days
Supply, recovery port
100kg detector: Liq.Xe supply and recovery
Supply (2 days) recovery(0.85 days)
L
ML
M
HM
H
We found that the PMTs work even at -90℃
60Co source on the detector
6 PMT test data
Limit vertex position using( of 6PMTs)/ (average of 6PMTs)
100kg detector: Test data Observed spectrum
SimulationThe observed spectrum is consistent with the simulation
All<1
All<1
Shield of 100kg detector
• OFHC vacuum chamber, OFHC shield(5cm thick), Lead shield (15cm), Boron (10cm), Polyethylene(15 cm), Radon shield (EVOH sheet)
Installation in May, June
Installation of ShieldDoor part is already installed. (May, 2003)
Moved into clean room in Kamioka mine.
Lead shield (15cm thick)OFHC shield(5cm)
Full shield will be installed by the end of June, 2003.
Vertex/energy reconstruction (MC simulation)• Make PMT hitmaps
• Maximize the likelihood:
F(x, y, z; i): acceptance of scintillation light for i-th PMT from (x, y, z). GEANT based simulation gives F(xg, yg, zg, i) on a grid with 2.5cm spacing. F(x, y, z, i) is linearly interpolated by using F(xg, yg, zg, i).
PMT
n
nL )
!
)exp(Log()Log(
L: likelihood: F(x, y, z) x (total p.e./total acceptance)n: observed number of p.e.
Typical 1MeV alpha ray
Red: true vertexGreen: reconstructed
0.88cm (68%)
1MeV 300keV
1.40cm (68%)
=62keV(gauss fit)
=33keV(gauss fit)
Vertex/energy resolution (MC)
Uniformly distributed source in the fv (20cm cube)
2 phase detector(S.Suzuki et al.)
100kg detector: background level( expectation by simulation )
0.1ppm 85Kr
85Kr~0.01ppm
/kg/
day
/keV
• Gamma rays from 238U, 232Th, 40K outside the chamber.238U: 2.4Bq, 232Th: 1.4Bq, 40K: 0.86Bq, determined by a HPGe.• Events were reconstructed by the reconstruction tool.
100kg all volume estimated
100kg 20cm cube, ½ PMT cut
Efficiency: 60% @ 100keV 2.4% @ 10keV
Purification by distillation• R/D of purification system Simple distillation system for Kr Theoretically, 1/1000 reduction Process power: 0.6kg/hr
Buffer tank
Compressor
Heatexchanger
Purified Xe
Xeinput
Refrigerators
Purification tower ~3m13 stages
Heater
Getter
GXe flow
LXe
Kr
Tower
Boiling point: Xe=165K, Kr=120K, Ar=87K
Test this purification system in 2003.
Next step: 800kg detector
• 800kg liquid Xe
• 642 2-in PMTs
• 77% photo-coverage
• ~5 p.e./keV
80cm diameter
/kg/
day
/keV
pp
7Be
, 8x1021 yr
External background in 800kg detector• Dominant contribution is from PMT
• Assuming further 1/10 reduction of PMTs BG
external ray (60cm, 346kg)
external ray (40cm, 100kg )
Dark matter (10-8 pb, 50GeV, 100 GeV)
Dark matter sensitivity800kg detector
Spin independent Spin dependent
spectrumSeasonal variation
Requirements in background for 800kg detector
ExternalEnvironmental rays: 15cm Pb + 5cm OFHC or water shield
Fast neutron recoil at 10 keV : < 1/10000 of environment
Thermal neutron absorption: < 1/400 of environment
Internal
85Kr: < 0.35 ppt of Kr (by distillation)42Ar, 39Ar: < 0.1 ppm Ar (by distillation)
Radon: < 1microBq/m3
U/Th in Liq.Xe: < 10-14 g/g
~2m of water shield
Conclusion• Large volume liquid Xe detector is quite effective fo
r dark matter, double beta decay and low energy solar neutrinos.
• R&D is going on using 100 kg detector.• Using the 100 kg detector, we will test vertex and en
ergy reconstruction, self-shielding, and purification of liquid Xe.
• The next step is 800 kg detector. The 800 kg detector is able to search for dark matter with 4 orders of magnitude better sensitivity than current experiments.
• Final goal of the XMASS project is 10 ton class detector for multi-purpose astro-particle physics.