Satoshi SUZUKIWaseda University
Present status and perspective of cryogenic liquid detectors
13/Mar./2006Cryodet @ Gran Sasso
Recent Development of Cryogenic liquid detectors
MEG
XMASS
Double Phase Detector
ICARUS Pioneer of LAr TPC
CLEAN(LNe)
DAMA(LXe)ZEPLIN I
Simple scintillation detector
DM search
First big LXe detector foreexperiment
Energy resolutionTiming resolutionPosition resolution
XMASS ⅡZEPLIN Ⅱ 〜ⅣXENONWALP(LAr)
The biggest LXe detectorfor DM and pp 7Be solar
NuMIT2K
LXe TPCTechnology of LAr TPC was established by ICARUS.
Self Shielding
Enlargement : 1kg---several steps---300ton(600ton)- 〜 10kton(final)
Demonstrate the potential of LXe detector
MEG Experiment• Signal
• E = m/2 = 52.8MeV
• Ee = m/2 = 52.8MeV
• = 180o
• Time coincidence
ee
Expected sensitivity 〜 order of 10-14
(present limit = 1.2x10-11)
Liquid Xe scintillation
Large light output yieldWph(1MeV e) = 22.4eV
Pile-up event rejection
Fast response and short decay time
Uniform
NaIBGO
GSO
LSO LXe
Effective Atomic number
50 73 58 65 54
Density (g/cm3) 3.7 7.1 6.7 7.4 3.0
Relative light output (%)
100 1520-40
45-70
80
Decay time (nsec)
230 300 60 404.2,22
,45
MEG Xenon Detector
• Active volume ~800l is surrounded PMTs on all faces
• ~850PMTs in the liquid• No segmentation• Energy
– All PMT outputs
• Position– PMTs on the inner face
• Timing– Averaging of signal arrival time of
selected PMTs
■ 70 liter active volume (120 liter LXe in use)■ 238PMTs immersed in LXe■ Large enough to contain 50MeV event(17X0)■ Performance test using
– 10, 20, 40MeV Compton beam– 60MeV Electron beam– from 0 decay
Large Prototype
Energy Resolutions
55 MeV
83 MeV
Exe
non[
n ph]
83 MeV to Xe
55 MeV to Xe
Right is a nice function of gamma energy
PSI 2004TERAS 2003alpha
Energy Resolution vs Energy
Examples of Reconstruction
(40 MeV gamma beam w/ 1 mm collimator)
55 M
eV
high gainnormal gain
110 psec 103 psec
LYSO Beam L-R depth reso.
110 64 61 = 65 = 56 33 psec
103 64 61 = 53 = 43 31 psec
No
rma
l g
ain
Hig
h
ga
in
A few cm in Z
Absolute timing, Xe-LYSO analysis
Liquid phase circulation system
1 m
2.5 m5 m
Absorption length > 5m in 10hours
PMT Development Summary1st generation R6041Q 2nd generation R9288TB 3rd generation R9869
228 in the LP (2003 CEX and TERAS)
127 in the LP (2004 CEX)
111 In the LP (2004 CEX) Not used yet in the LP
Rb-Sc-Sb
Mn layer to keep surface resistance at low temp.
K-Sc-Sb
Al strip to fit with the dynode pattern to keep surface resistance at low temp.
K-Sc-Sb
Al strip density is doubled.
4% loss of the effective area.
1st compact version
QE~4-6%
Under high rate background,
PMT output reduced by 10
-20% with a time constant of
order of 10min.
Higher QE ~12-14%
Good performance in high rate BG
Still slight reduction of output in very high BG
Higher QE~12-14%
Much better performance in very high BG
PMTs
liquid XeVolume for shielding
Fiducial volume
BG
nor
ma
lize
d b
y m
ass
6 orders of magnitude reduction for gamma rays below 500keV
Fiducial volume
Self-shielding for low energy events
◆ Isotope separation
124Xe 126Xe 128Xe 129Xe 130Xe 131Xe 132Xe 134Xe 136Xe(0.10%) (0.09% ) (1.92%) (26.4%) (4.07%) (21.2%) (26.9%) (10.4%) (8.87%)
Even enrichedOdd enriched
2/0
nucleon
Separate here
Dark Matter ⅠSolar neutrino
Dark Matter ⅡSpin dependent
Abundance of natural Xe
Strategy of the scale-up100kg Prototype 800kg detector
10 ton detector
〜 30cm〜 80cm
〜 2.5mR&D
Dark matter search
Multipurpose detector
(solar neutrino, …)
We are here
100 kg prototype detector In the Kamioka Mine(near the Super-K)
Gamma ray shield
OFHC cubic chamber
Liq. Xe (31cm)3
MgF2 window
54 2-inch low BG PMTs
16% photo- coverage
Hamamatsu R8778
2,700 m.w.e.
→ Vertex reconstruction works well
Performance of the vertex reconstruction Collimated ray source run from 3 holes (137Cs, 662keV)
DATA
MC
hole Ahole Bhole C
ABC+++
65keV@peak(/E ~ 10%)
Similar peak position in each fiducial.No position bias
Performance of the energy reconstruction Collimated ray source run from center hole
137Cs, 662keV
→ Energy reconstruction
works well
All volume20cm FV10cm FV
800kg detector A tentative design (not final one)
Total 840 hex PMTs immersed into liq. Xe 70% photo-coverage Radius to inner face ~43cm
12 pentagons / pentakisdodecahedron
This geometry has been coded in a Geant 4 based simulator
Eth = 5 keVee~25 p.e.
Hamamatsu R8778MOD(hex)
12cm
5.4c
m5.
8cm
(ed
ge
to e
dg
e)
0.3cm(rim)
c.f. R8778 U 1.8±0.2x10-2 Bq Th 6.9±1.3x10-3 Bq40K 1.4±0.2x10-1 Bq
Hexagonal quartz window Effective area: 50mm (min) QE <~25 % (target) Aiming for 1/10 lower background than R8778
Prototype has been manufactured already Now, being tested
Kr 0.1ppm
DM signal(10-6 pb, 50GeV,100 GeV)
0 200 400 600 800
1
102
10-2
10-4
10-6
cpd/
kg/k
eVenergy (keV)
Target = Xe
85Kr makes BG in low energy region
Kr can easily mix with Xe because both Kr and Xe are rare gas
Commercial Xe contains a few ppb Kr
Kr contamination
~3mLower
Higher
~1%
~99%
Purified Xe: 3.3±1.1 ppt Kr (measured)
Off gas Xe:330±100 ppb Kr(measured)
Raw Xe: ~3 ppb Kr
(178K)
(180K)Operation@2atm
• Processing speed : 0.6 kg / hour• Design factor : 1/1000 Kr / 1 pass• Purified Xe : Off gas = 99:1
Boiling point
(@2 atm)
Xe 178.1K
Kr 129.4K
Xe purification system
Now (prototype detector) Goal (800kg detector)
ray BG ~ 10-2 cpd/kg/keV
→ Increase volume for self shielding
→ Decrease radioactive impurities in PMTs (~1/10)
238U = (33±7)×10-14 g/g
→ Remove by filter
232Th < 23×10-14 g/g (90% C.L.)
→ Remove by filter (Only upper limit)
Kr = 3.3±1.1 ppt
→ Achieve by 2 purification pass
Very near to the target level!
1/100
1/33
1/12
1/3
10-4 cpd/kg/keV
1×10-14 g/g
2×10-14 g/g
1 ppt
Summary of BG measurement
W- phase Xe Detector (Direct & proportional scintillation )
Dri
ft T
ime
E
anode
e-
grid
cathode
~1μ
sec
~40
n sec
Gas
Liquid
S2
S1
•Signal from Double Phase Xe
direct proportionaldirect
proportional
direct
drift timedrift time
42000photon/MeVDecay time 45nsec
•Recoil /γ ray Separation
>99% γ ray rejection>99% γ ray rejection
22 keV gamma ray
Recoil Xenon (neutron source)
Direct scintillation(S1)
Pro
por
tion
al s
cin
till
atio
n(S
2)
Gas Xe
PMT(HAMAMATSU
R8778 x 7)
EdOFHC
PTFE
(Field shaping ring)
MgF2(cathode)
MgF2(cathode)
anode
grid
grid
Liq Xe
Gas Xe
160mm
220mm
165mm
Liquid Surface
15 kg Double Phase Xe Detector
PTFEField Shaping Ring
MgF2 Window(Cathode:gold coated mesh)
Anode - Grid Set
PMT
15kg Chamber Construction
15 kg Chamber Construction
Shield
3D-double phase xenon detector
Multi-purpose detector
WIMPs136Xe double decaypp 7Be solar
If we have pure xenon which is free from radioactive impurities, proportional scintillation is very useful.
3D W-phase test chamber
PMT: Hamamatsu R5900-06MOD•1inch square type•QE=5%•Work in LXe
Liquid Xe
Gas Xe
Circulation pumpGetter
Recirculation purification
Simulation (for 100 keV electron)
•Distance between PMT and anode: 3 cm•proportional scintillation
:1 mm Gaussian•Collection of electrons
:80%•PMT Coverage : 20%•QE : 5 %
0
0.5
1
1.5
2
2.5
3
Generated Photons
É–[mm]
103 104 105 106 107
1ph/e
1000ph/e
Position resolution(x,y)
σxy < 1 mm will be possible by good adjustment of PMTsUse multi -anode PMTs for double decay experiment
5.9 keV ray from 55Fe 22 keV ray from 107Cd
Low energy threshold for pp 7Be solar
< few keV
Proportional scintillation
Energy spectrum for low energy rays
Independent of detector size
ΔZ ~ few 100 m
ray rejection for 0 decay experiment
S1 one signalS2 more than two
Compton scattering events
WIMPs
Low background environmentsShielding
Detector
low Eth <10 keV
large mass
particle ID
energy resolution
γ/βID
low Eth
huge mass 〜 10 ton
real time
self-shielding
particle ID (WIMPs, neutrons,)
0 decay pp, 7Be solar
Low energy detection by 3D-double phase detector in Underground
What is the most important in the future?
How to collect photon effectively?
Improve photon detector, PMT …
The best is to find a wave length shifter.
Maybe yes
No
Small detector
Big detector
Rayleigh scattering 1/∝ 4
Attenuation length vs Wavelength()T. Ypsilantis et al.(‘95)
MgF2 : 1.45Refractance quartz : 1.56 LXe :
1.60
15.3 %1.75 pe/keV (QE:25%)
Reflectance for PTFE : 0.90Absorption length of LXe : 1 m
Scattering length : 40 cm
15 kg W-phase detector
Reflectance for PTFE :〜 0.99Absorption length of LXe :〜 20 m
Scattering length :〜 3m
〜 80 %〜 8 pe/keV
λ= 175 nm
λ= 350 nm
Light collection efficiency
TEA doped rare gas experiment
h(VUV) + TEA → TEA*Ar2* + TEA → Ar + Ar + TEA*h(VUV) + TEA → TEA+ + eAr2* + TEA → Ar + Ar + TEA+ + e
Ar* + Ar + Ar → Ar2* + ArAr2* → Ar + Ar + h(VUV)
Competitive process
M.SUZUKI et al. (1987)
Emission from TEA
Is it possible to apply to liquid?
h(VUV) + TEA → TEA+ + e(Ar2* + TEA → Ar + Ar + TEA+ + e)
h(VUV) + TEA → TEA+ + e(Xe2* + TEA → Xe + Xe + TEA+ + e)
QE = 0.23
QE 〜 1
Nobody check visible(UV) light!Excitation process should be occurred.Especially to LAr because of small QE.
Photo ionization effect was observed for both liquid.
LAr
LXe
The end
Rn assay with prototype detector• 238U series
– 222Rn(1/2 = 3.8d, 3.3MeV beta), …
• 232Th series – 220Rn(55s, 2.3MeV beta[64%]), …
214Bi 214Po 210Pb
1/2 =164sec (Emax=3.3MeV) (7.7MeV)
212Bi 212Po 208Pb
1/2 =299nsec (Emax=2.3MeV) (8.8MeV)
(BR=64%)
No candidate found
Observed coincident events