Study of Neutrino-Electron Scattering with CsI(Tl) Scintillating

Crystal Detector

TEXONO Physics Program on CsI(Tl) Detector

Shielding and CsI(Tl) Detector Design

Data Analysis Techniques

Cut Summary

Background Understanding and Suppression

Status and Plans

Muhammed Deniz1,2

1: METU, Ankara, Turkey2: IoP, Academia Sinica,

Taiwan

On behalf of TEXONO collaboration@ 2006 Workshop on the Underground Experiment –

Extension of KIMS + TEXONO Collaboration

TEXONO Physics Program on CsI(Tl) detector

Region of Interest for e -ve scattering

CsI(Tl) (186 kg) : attempt a measurement of Standard Model (ee-)

sinw at MeV range

e + e- e + e-

Uncertainties in the low energy part of reactor neutrino for SMeehigher energies (T>2 MeV)

KS Expt. : Detector Configuration

16 ch, 20 MHz, 8 bit

10052031237020406

982297827156609014

3820694447481599

390889316878811734

4140463366928310

351664498050430511

2319633294452721

1322093675355592425

10126656162589642

875173747576575486

8577727079918895

CsI(Tl) crystal layout (93 cry. 186 kg)

40 cm-target crys.40 cm-veto crys.20+20 cm-veto crys.Plastic

CsI(Tl) Array : Highlights

Period II Data Volume : Total ~ 110 / 50 days ON/OFF

186 kg mass ; 20+20 and 40 cm length (longest commercial prod.) CsI(Tl) crystals

Detector Threshold: 3 MeV

Energy: total light collection

z-position: the variation of the ratio

Energy & Z-position info:

10% FWHM @ 660 keV

Z-position resolution is

(z) = 2 cm @ 660 keV

(z) <2 cm @ higher energies

RL~ QQE

)/()( RLRL QQQQR

a) Alpha Event Cut

• having fast decay time

Checking: Alphas are located around 2 MeV

Selection: Mean Time Method: tav vs. q and Double Charge Method: compare total charge with partial charge

Alpha Event Pulse

Normal Event Pulse

Data Analysing Techniques - Defining Cuts

Narrow Pulse

Normal Pulse

0 cm 40 cm

40 cm long crystal No cut

Definition:

Selection: Both side peak means initially taken as 0 & 40.

Cut: 4 cm from both sides

)21/()21( QQQQZ

b) Z-position Cut:

Data Analysis Techniques - Defining Cuts

Data Analysis Techniques - Defining Cuts

Veto cut: Reject Cosmic ray Single-hit cut: Anti Compton effectPSD cut : Alpha particleZ-pos cut : Both veto and S.H. effect

Data Analysis Techniques - Calibration1) Z-POSITION CORRECTION:

BEFORE CORRECTION AFTER CORRECTION

2) SLOPE CORRECTION:

AFTER CORRECTION

BEFORE CORRECTION

3) ENERGY CORRECTION:

ON spectrum 0.441/day/kg in Period II

OFF spectrum 0.423/day/kg in Period II

* 37 Crystals (40 cm) * Mass 59.2 kg* Basic cuts + Alpha cut + 4 cm Z-cut

ON and OFF Energy Spectra

208Tl (2614keV)

40K (1460 keV)

137Cs (662 keV)

OFF spectrum in all energy range

ON&OFF spectra in 3-8 MeV

energy range

Two Type :1. Radioactive Contaminants

Decays of radioactive contaminants mainly 232Th and 238U chain produce background in the region of interest.

• Estimate the abundance of 137Cs, 238U and 232Th inside the detector.

• Figure out the contribution of 238U and 232Th chains to the background.

2. Environmental Background

Cosmic Ray muons, Products of cosmic ray muons, Spallation neutrons and some radioactive elements like 60Co, 208Tl• Estimate the background related to cosmic rays due to

inefficiency suppression.• Understand and suppress the contribution of 208Tl to the

background in region of 3-4 MeV.

Background Understanding

Background Understanding

Radioactive Contaminants– IDEA: By monitoring the timing and position information related β-α

or α-α events can provide distinct signature to identify the decay process and the consistency of the isotopes involved.

Environmental Backgrounds– IDEA: multiple-hit analysis can give us very good understanding

especially Tl-208 and cosmic related background in the region of interest

• cosmic– By comparing cosmic and not-cosmic multiple-hit spectra. – By examining the pair-production phenomena in not-cosmic multiple-hit

spectra.

• Tl-208– By examining multiple-hit spectra as well as simulation of Tl-208 decay

chain energies to understand/suppress background in the region of 3-4 MeV.

Intrinsic 137Cs Level

137Cs contamination level in CsI was drived ==> (1.55 ± 0.02 ) X 10-17 g/g

31.3 kg-day of CsI(Tl) data was analysed.

β

α

Data: The total of 40 crystals with data size of 1725 kg·day was analyzed.

i) 214Bi(-)→ 214Po(,164s) → 210Pb

Intrinsic U and Th Contamination Level

T1/2 = (163 ±8) s

238U abundance = 0.82 ± 0.02 x10-12 g/g

iii) 220Rn → 216Po0.15s) → 212Pb

T1/2 = (±s

232Th abundance2.23 ± 0.06 x 10-12 g/g

ii) 212Bi(-,64%) → 212Po(, 299ns) → 208PbSelection: - pulse followed by a large pulseSelection: 1st pulse is shaped &

2nd pulse shaped

Selection: two events with time delay less than 1s

β

α

T1/2 = (± 37 ns.

232Th abundance = 2.3 ± 0.1 x10-12 g/g

• Master Thesis results of Zhu Y. F. from Tsing Hua Univ. in Beijing (2006)

510

1170 1330

2100 The Sources are external

Background Understanding via Multi Hit

• Co-60 contamination

• 1173.2 keV 99.86% accompanied with 1332.5 keV 99.98%

• Tl Pair Production: One escape peaks

• (~ 2105 + 511 keV)

The source is internal.

2614 keV 99.79 % accompanied with

583 keV 86%

510.8 keV 22.6%

860 keV with 12.4%

Combination of Tl gammas can affect up to around 4 MeV Cosmic induced neutrons can be captured by the target nuclei 133Cs.

The Source is external

600

800

Cs-134 (n + 133Cs 134Cs)

• 97.6% 605 keV;

• 85.5% 796 keV

Background Understanding – Tl-208 and Cosmic Inefficiency

Study on Background in Statistically

2&3 Hit Approach for 4 – 8 MeVTwo-Hit:

Expected to Single-Hit ratio:Exp/SH = 0.82 4cm z-cut

= 0.96 for no z-cut

Three-Hit:

Expected to Single-Hit ratio:Exp/SH = 0.98 for 4cm z-cut

= 1.15 for no z-cut

Pair Production Approach for 4 – 8 MeVFor no z-cut

Expected to Single-Hit ratio:

Exp/SH = 1.03

For 4cm z-cut

Expected to Single-Hit ratio:

Exp/SH = 0.90

• To understand the contribution of cosmic rays to the background,

~ 926 kg*day data was analyzed for cosmic and not-cosmic multi-hit as well as pair production.

○○

There are two kinds of background events within our signal.

• one is matching well with reference -pulse (-)and

• the other is fast- falling ()…

Right side Right sideLeft side Left side

TYPE I TYPE II

2 Analysis

• Black – Recorded Pulse by FADC• Green – Reference pulse • Red - Reference pulse

2 Analysis

Cutting at this point, suppression 66%(.248/.727)

-square function

Red – events

Black – events

Preliminary Result of sin2W

g

The best fit of sin2W : 0.37 ± 0.13 at 3-8MeV

0.30 ± 0.22 at 3.5-8MeV

Ph.D. Thesis results of Dr. Lin Shin Ted (2006)

Expected Accuracy of sin2W with data size

130

Expected Result of Accuracy of e-e) and sin2W

Characteristics of the previous and current neutrino-e scattering experiments

CsI(Tl) cry.CsI(Tl) cry.

186 kg186 kg

3.0 3.0

1.8 (expect)1.8 (expect)

0.10.1

<20% (goal<20% (goal)

CF4 gasCF4 gas

21 kg21 kg

0.9 0.9

1.771.77

0.20.2

50%50%

Si(Li)Si(Li)

37.5 kg37.5 kg

0.60.6

5.25.2

0.0080.008

49%49%

FluorocarbonFluorocarbon

103 kg103 kg

3.13.1

0.780.78

0.10.1

53%53%

Plastic scin.Plastic scin.

15.9 kg15.9 kg

1.51.5

1.21.2

0.180.18

29%29%**

TEXONOTEXONONUMUNUMURovnoRovnoKurtchatovKurtchatovSavannahSavannahExperimentsExperiments

TargetTarget

Fiducial MassFiducial Mass

Thr. (MeV)Thr. (MeV)

Signal Evt./DaySignal Evt./Day

S / BS / B

Accuracy ofAccuracy of

((eee)e)

TEXONO and World status !

“Our aim is to measure ((eee) e) with <20% <20% accuracy.”

Our aim is to measure Sin2W value with <8% accuracy.

Thank you