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