xmass experiment and its double beta decay option

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XMASS experiment and its double beta decay option XMASS experiment for dark matter search and low energy solar neutrino detection Double beta decay option 18 th Sep. 2005, HAW05 workshop, Double beta-decay and neutrino masses S. Moriyama, ICRR

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XMASS experiment and its double beta decay option. 18 th Sep. 2005, HAW05 workshop, Double beta-decay and neutrino masses S. Moriyama, ICRR. XMASS experiment for dark matter search and low energy solar neutrino detection Double beta decay option. 1. Introduction. Solar neutrino. - PowerPoint PPT Presentation

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Page 1: XMASS experiment and its double beta decay option

XMASS experiment and its double beta decay option

XMASS experiment for dark matter search and low energy

solar neutrino detection Double beta decay option

18th Sep. 2005,HAW05 workshop,Double beta-decay and neutrino massesS. Moriyama, ICRR

Page 2: XMASS experiment and its double beta decay option

1. Introduction

Dark matter

Double beta

Solar neutrino

What’s XMASS

Xenon MASSive detector for solar neutrino (pp/7Be) Xenon detector for Weakly Interacting MASSive Particles (DM search) Xenon neutrino MASS detector ( decay)

Multi purpose low-background experiment with liq. Xe

Page 3: XMASS experiment and its double beta decay option

Why Liquid Xenon?

General properties:Large scintillation yield (~42000photons/MeV ~NaI(Tl))Scintillation wavelength (175nm, direct read out by PMTs)Higher operation temperature (~165K, LNe~27K, LHe~4K)Compact (2.9g, 10t detector ~ 1.5m cubic) Not so expensiveWell-known EW cross sections for neutrinos

External gamma ray background:Self shielding (large Z=54)

Internal background:Purification (distillation, etc)No long-life radio isotopes Isotope separation is relatively easyNo 14C contamination (can measure low energy)

Circulation

Page 4: XMASS experiment and its double beta decay option

Key idea: self shielding effect for low energy signals

Large Z makes detectors very compact Large photon yield (42 photon/keV ~ NaI(Tl))

Liquid Xe is the most promising material.

PMTs

Single phaseliquid Xe Volume for shielding

Fiducial volume

23ton all volume20cm wall cut30cm wall cut (10ton FV)

BG

nor

ma

lize

d b

y m

ass

1MeV0 2MeV 3MeV

Large self-shield effect

External ray from U/Th-chain

Page 5: XMASS experiment and its double beta decay option

Strategy of the XMASS project

~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

Good results

Confirmation of feasibilities of the ~1ton detector

Double beta decay option?

Page 6: XMASS experiment and its double beta decay option

3kg FV prototype detector

In theKamioka

Mine(near the

Super-K)

Liq. Xe  (31cm)3

MgF2 window

54 2-inch low BG PMTs

Gamma ray shield

OFHC cubic chamber

• Demonstration of reconstruction, self shielding effect, and low background properties.

16% photo-coverage

HamamatsuR8778

Page 7: XMASS experiment and its double beta decay option

PMT

n

nL )

!

)exp(Log()Log(

L: likelihood

: F(x,y,z,i)

x total p.e. F(x,y,z,i)

n: observed number of p.e.

Vertex and energy reconstruction

=== Background event sample === QADC, FADC, and hit timing information are available for analysis

F(x,y,z,i): acceptance for i-th PMT (MC)VUV photon characteristics:

Lemit=42ph/keVabs=100cm

scat=30cm

Calculate PMT acceptances from various vertices by Monte Carlo. Vtx.: compare acceptance map F(x,y,z,i) Ene.: calc. from obs. p.e. & total accept.

Reconstructedhere

FADC Hit timing

QADC

Reconstruction is performed by PMT charge pattern (not timing)

Page 8: XMASS experiment and its double beta decay option

Source run( ray injection from collimators) I

DATA

MC

Collimator A Collimator B Collimator C

A B C

+++Well reproduced.

Page 9: XMASS experiment and its double beta decay option

Source run( ray injection from collimators) II

Good agreements. Self shield works as expected. Photo electron yield ~

0.8p.e./keV for all volume

Gamma rays

Z= +15Z= -15

137Cs: 662keVDATAMC

PMTSaturationregion

-15 +15cm -15 +15cm

~1/200

~1/10

Reconstructed Z Reconstructed Z

Arb

itrar

y U

nit

10-1

10-2

10-3

10-4

10-5

10-1

10-2

10-3

10-4

10-5

60Co: 1.17&1.33MeV DATA MC

No energycut, onlysaturation cut.BG subtracted=2.884g/cc

Page 10: XMASS experiment and its double beta decay option

Background data

MC uses U/Th/K activity from PMTs, etc (meas. by HPGe). Good agreement (< factor 2) Self shield effect can be clearly seen. Very low background (10-2 /kg/day/keV@100-300 keV)

REAL DATA MC simulation

All volume20cm FV

10cm FV(3kg)

All volume20cm FV

10cm FV(3kg)

Miss-reconstruction due to dead-angle region from PMTs.

10-2/kg/day/keV

Aug. 04 run

3.9dayslivetime

~1.6Hz, 4 fold, triggered by ~0.4p.e.

Eve

nt r

ate

(/kg

/day

/keV

)

Page 11: XMASS experiment and its double beta decay option

Current results• 238U(Bi/Po): = (33+-7)x10-14 g/g

• 232Th(Bi/Po): < 63x10-14 g/g

• Kr: < 5ppt

Internal background activities

Factor <~30 (under further study)

Achieved by distillation

Factor ~30, but may decay out further

Goal to look for DM by 1ton detector

1x10-14 g/g

2x10-14 g/g

1 pptx5

x32

x33

Very near to the target level of U, Th Radon and Kr contamination.

Page 12: XMASS experiment and its double beta decay option

Distillation to reduce Kr (1/1000 by 1 pass) Very effective to reduce internal impuritie

s (85Kr, etc.) We have processed our Xe before the m

easurement.

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 after Kr-enrichment)

Off gas Xe:330±100 ppb Kr(measured)

Original Xe: ~3 ppb Kr

Page 13: XMASS experiment and its double beta decay option

1 ton (100kg FV) detector for DM Search

Solve the miss reconst. prob. immerse PMTs into LXe Ext. BG: from PMT’s Self-shield effect demonstrated Int. BG: Kr (distillation), Radon Almost achieved

external ray (60cm, 346kg)

external ray:(40cm, 100kg )

/kg/

day/

keV

Dark matter(10-6 pb, 50GeV,100 GeV)Q.F. = 0.2 assumed

pp

7Be

8x10-5/keV/kg/d

“Full” photo-sensitive,“Spherical” geometry detector

80cm dia.

Achieved

0 100 200Energy(keVee)~800-2” PMTs (1/10 Low BG)

70% photo-coverage ~5p.e./keVee

Page 14: XMASS experiment and its double beta decay option

More detailed geometrical design A tentative design (not final one) 12 pentagons / pentakisdodecahedron

This geometry has been coded in a Geant 4 based simulator

Hexagonal PMT~50mm diameter

Aiming for 1/10 lower BG than R8778 R8778: U 1.8±0.2x10-2 Bq Th 6.9±1.3x10-3 Bq 40K 1.4±0.2x10-1 Bq

Page 15: XMASS experiment and its double beta decay option

Expected sensitivity

Large improvements expected.

XMASS(Ann. Mod.)

XMASS(Sepc.)

Edelweiss Al2O3

Tokyo LiF

Modane NaI

CRESST

UKDMC NaI

NAIAD

XMASS FV 0.5ton yearEth=5keVee~25p.e., 3 discoveryW/O any pulse shape info.

10-6

10-4

10-8

10-10

Cro

ss s

ectio

n to

nuc

leon

[p

b]

10-4

10-2

1

102

104

106

Plots except for XMASS: http://dmtools.berkeley.eduGaitskell & Mandic

Page 16: XMASS experiment and its double beta decay option

Double beta decay option

Page 17: XMASS experiment and its double beta decay option

BG for double beta decay signals with conventional XMASS detector

2not yet observed. NA 8.9% Q=2.467MeV, just belo

w 208Tl 2.615MeV rays

Self shielding of liquid xenon is not very effective for high energy rays.

rays from rock & PMTs need to be shielded.

23ton 2.5m dia. sphere

15ton 2.1m dia.

10ton (1.9m dia. )

100% 136Xe01025yr<m>~0.2-0.3eV

100% 136Xe 28x1021yr

Eve

nt r

ate

(keV

-1kg

-1y-1

)

Page 18: XMASS experiment and its double beta decay option

One of possible solutions

Put room temperature LXe intoa thick, acrylic pressure vessel (~50atm).Symbolically…

Wavelength shifter inside the vessel.

We already have 10kg enriched 136Xe.

Merit: Xe can be purifiedeven after experiment starts!

Page 19: XMASS experiment and its double beta decay option

Expected 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 transp., 20% PMT coverage, 25% QE 57keVrms @ Q=2.48MeV

1yr, 10kg measurement 1.5 x 1025 yr <m>=0.2~0.3eVc.f. DAMA > 7 x 1023 yr (90%)If U/Th ~ 10-16 g/g + larger mas

s <m>~0.02-0.03eV will not be BG thanks to high resolution!!

57keVrms

expected

U+Th normalized for 10kg, 1yr

Page 20: XMASS experiment and its double beta decay option

R&D items Pressure test Wavelength shifter Scintillation yield Possible creep effect on acrylic material Degas from acrylic surface BG consideration (time anal., plastic scinti. vessel) Detector design

c.f. wavelength shifter: M.A.Iqbal et al., NIMA 243(1986)459 L. Periale et al., NIMA 478(2002)377 D. N. McKinsey et al., NIMB 132 (1997) 351

Pressure vessel PMTs

Useful for any scintillators

Double focus detector• Cheap• Easy• Safe

Water sheild

Scintillation light

-

Page 21: XMASS experiment and its double beta decay option

Pressure test vessel

Test vessel held 80 atm water!!

valve

110mm-dia.

120mm length

50mm-dia., 50mm length~98cc

water

Page 22: XMASS experiment and its double beta decay option

R&D study for wavelength shifter DC light source: excimer xenon lamp

Vacuum vessel, signal PMT and monitor PMT

• Vacuum vessel ~80cm diameter• Signal and monitor PMTs   R8778 for XMASS• Sample fixed in 50mm dia. holder• Beam splitter: MgF2 tilted by 45 deg.

172nm

monitor PMT

PMT

sample

0

100

160 170 180 190 (nm)

Wavelength ~ LXe scintillation light

Arb

itrar

y un

it

Page 23: XMASS experiment and its double beta decay option

TPB in PS Famous WLS for VUV lights TPB: Tetraphenyl butadiene This measurementTPH: p-terphenylDPS: Dephenyl stilbeneSodium salicylate Doped in a polystyrene films 0.5, 1.0, 2.0, 4.0, 8.0, 16.0% (in weight)Ref. systematic study ondoped films for 58nm and 74nm,D. N. McKinsey et al.,NIMB, 132 (1997) 351-358

0.5% TPB doped PS, 100m

Page 24: XMASS experiment and its double beta decay option

TPB 0.5% doped PS Two measurements for systematic study (1) Gap between PS and PMT: PS n=1.59 Due to total reflection<39deg. light go into PMT Solid angle  11% Correction applied(2) Optical grease btw PS and PMT: grease n=1.47 Light to orange region go into PMT (67deg., 39deg.)  Solid angle 50% Correction applied Efficiency 37+/-6% is obtained for 0.5% TPB PS. However, 2% TPB PS does not give consistent

results. Further careful study needed.

PMT39deg. Quartz

n=1.5-1.6

PMT

67deg.

Page 25: XMASS experiment and its double beta decay option

Background due to 8B solar neutrinos

8B solar neutrinos for double beta decay searchA. A. Klimenko, hep-ph/0407156,

8B solar neutrinos willbe background for136Xe double beta decay search.4.0x1027y 23meV

Need Ba daughter tag,two track ID,or ??

Ge is safe because ofits high energy res.

T21/2 = 2.2x1022y

T21/2 = 4.0x1027y

FWHM=60keV

Page 26: XMASS experiment and its double beta decay option

Summary XMASS experiment: dark matter, low energy solar neutrino, a

nd double beta decay observation. With 3kg FV R&D detector, we have demonstrated event reco

nstruction, self shielding, and low radioactive contamination in xenon.

(1)238U(Bi/Po) = (33+-7)x10-14 g/g

(2) 232Th(Bi/Po) < 63x10-14 g/g

(3) Kr < 5ppt.

(4) Background @ 200keV ~10-2/kg/keV/day 100kg FV XMASS detector is expected to give ~100 improvem

ent for current dark matter search. For double beta decay option, another design is discussed. Wavelength shifter (0.5% TPB in PS) gives 37+/-6% conversi

on efficiency for 172nm light. Further R&D is ongoing for double beta decay option.

Page 27: XMASS experiment and its double beta decay option

Ge detector case

Ge case, 4.2x1027y is safe (FWHM 5keV)

Page 28: XMASS experiment and its double beta decay option

Estimation for the size of the water tank

Back of an envelope estimation:

1. 208Tl 2.6MeV gamma rays from the rock

2. Compton scattered gamma by water does not contribute.

3. Gamma flux of 208Tl based on measured value in the mine.

Attenuation coeff. of 2.614MeV in water : 4.27x10-2 cm-1 (1/70 by 1m)Gamma ray flux in the mine, 2.615MeV: 0.07cm2/secSurface area of 10kg liquid xenon (24cm diameter): 2x103cm2

Probability to deposit 2.6MeV when the gamma ray incident : 10%Water thickness: t (m)

BG 1event/1yr ( 2x10-9! )0.07 x 2x103 x 0.1 x exp(-4.27 t) x 86400 x 365 = 1 t =4.7m

Page 29: XMASS experiment and its double beta decay option

Distance to the PMT’s 20’’ PMT for Super-Kamiokande  208Tl gamma ray ~10/sec/PMT Use 10 PMT’s  To make 1event/1yr background, 10 x 10 x (0.122)/4t2 x exp(-4.27 t) x 86400 x 365 = 1

t=3.3m 3.3m 13m

10m

Water tank

Rough calculation gives: 13m in height 10m in diameter

Page 30: XMASS experiment and its double beta decay option

0.01

0.10

1.00

10.00

100.00

160 260 360 460 560 660 760

Wavelength [nm]

Pho

toca

thod

e R

adia

nt S

ensi

tivity

[mA

/W]

Qua

ntum

Effi

cien

cy [%

]

Quantum Efficiency

Quantum Efficiency

Fig.1. Xe2*エキシマランプの分布スペクトル

0

10

20

30

40

50

60

70

80

90

100

150 155 160 165 170 175 180 185 190 195 200波長(nm)

相対

強度

spectral

0

10

20

30

40

50

60

70

80

90

100

3500 4000 4500 5000 5500 6000

wave length A

spectr

al

spectral

Page 31: XMASS experiment and its double beta decay option

spectrum (light source)

0

10

20

30

40

50

60

70

80

90

100

150 155 160 165 170 175 180 185 190 195 200

Wave length [nm]

Page 32: XMASS experiment and its double beta decay option

0.75

0.8

0.85

0.9

0.95

1

150 155 160 165 170 175 180 185 190 195 200

tran

smitta

nce

MgF2 transmittance

Wave length [nm]

Page 33: XMASS experiment and its double beta decay option

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 ~30 % (target) Aiming for 1/10 lower background than R8778

Prototype has been manufactured already Now, being tested

Page 34: XMASS experiment and its double beta decay option

McKinsey: Excitation by 58, 74nm