1. On behalf of TEXONO collaboration
Study of Neutrino-Electron Scattering with a Fine-Grained CsI(Tl) Scintillating Crystal Detector
Muhammed Deniz1,2 1: METU, Ankara, Turkey 2: IoP, Academia Sinica, Taiwan
On behalf of TEXONO collaboration
Introduction
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

2. Introduction HISTORY Initiate : Chang Chung-Yung 1996
First Collab. Meeting/Official Start : October 1997
First Paper : October 1998
KS Reactor Experiment Installation : June 2000
First Ph.D. : Liu Yan , July 2000
First Physics Data Taking : June 2001.
First Physics Results: Dec 2002.

3. KS NPS -II : 2 cores  2.9 GW
KS  Lab: 28m from core#1
~102m from core#2
Total flux about 5.6x1012 cm-2s-1

4. Kuo-Sheng Reactor Neutrino Laboratory
Front Gate
Front View (cosmic vetos, shieldings, control room …..)
Control Room
Inner Target Volume

5. Why Reactor Neutrino’s ?
properties are not fully understood intense -source
Reactor : high flux of low energy (MeV range) electron anti- neutrinos.
NEUTRINO INTERACTIONS ON CsI(Tl)
For (e-e), both NC & CC and their interference term contribute
e + e e + e-

6. TEXONO Physics Program on CsI(Tl) detector
CsI(Tl) (186 kg) :
attempt a measurement of Standard Model (ee-)
 sinw at MeV range
e + e e + e-
Region of Interest for e -ve scattering
Uncertainties in the low energy part of reactor neutrino for SMee  higher energies (T>2 MeV)

7. TEXONO Program on Neutrino Interaction Cross- Sections
Phys. Rev. Lett. 90, (2003)
eN(MM)
eN(SM)
HPGe:
Mass: 1kg
Detection Threshold: 5keV
Background: 1 kg-1keV-1day-1
@12-60 keV
MM: µνe <1.3x10-10 µB
at 90% CL
Coh. (N) < 1 keV
ee-(MM)
MM (e) keV
ee- (SM)
SM (e) > 3 MeV

8. KS Expt. : Detector Configuration
16 ch, 20 MHz, 8 bit

9. KS Expt: Period II CsI(Tl) Detector
CsI(Tl) [ 186 kg ]
Connecting Board
Multi-Disks Array (800 Gb)
16 ch, 20 MHz, 8 bit

10. CsI(Tl) Array : Highlights
Period II Data Volume : Total ~ 110 / 50 days ON/OFF
186 kg mass ; 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% 660 keV
Z-position resolution is
(z) = keV
 (z) <2 cm @ higher energies

11. Data Analysis Techniques - Defining Cuts
Alpha Event Pulse
Normal Event Pulse
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

12. Data Analysis Techniques - Defining Cuts
40 cm long crystal No cut
b) Z-position Cut:
Definition:
Selection: Both side peak mean initially taken as 0 & 40 !
Cut: 4 cm from both sides
Narrow Pulse
Alpha Pulse
Normal Pulse
0 cm cm

13. Data Analysis Techniques - Defining Cuts
Veto cut: Reject Cosmic ray Single-hit cut: Anti Compton effect PSD cut : Alpha particle Z-pos cut : Both veto and S.H. effect

14. ON and OFF Energy Spectra
OFF spectrum in all energy range
ON&OFF spectra in 3-8 MeV energy range
208Tl (2614keV)
40K (1460 keV)
137Cs (662 keV)
ON spectrum /day/kg in Period II
OFF spectrum /day/kg in Period II
* 37 Crystals (40 cm)
* Mass 59.2 kg
* Basic cuts + Alpha cut + 4 cm Z-cut

15. Background Understanding
Two Type :
Radioactive Contaminants
[ Decays of radioactive contaminants mainly 232Th
and 238U chain produce background in the region of interest.
137Cs, 40K , and 60Co are in lower energy side but 208Tl can affect.
Estimate the abundance of 137Cs, 238U and 232Th inside the detector.
Figure out the contribution of 238U and 232Th chains to the background.
Understand and suppress the contribution of 208Tl to the background in region of 3-4 MeV.
2. Environmental Background
[ Cosmic Ray muons, Products of cosmic ray muons, Spallation neutrons and muon-produced isotopes
Figure out the contribution of environment effect.
Estimate and suppress the background especially related to cosmic rays due to inefficiency.

16. Background Understanding
Radioactive Contaminants
IDEA: 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.
REALIZATION:
By monitoring the timing features of α events and utilizing PSD technique.
By examining simulation as well as multiple hit spectra of Tl-208 decay chain energies to understand/suppress background in the region of 3-4 MeV.
Environmental Backgrounds
IDEA: multiple hit spectra can give us a clue about cosmic related background in the region of interest
By examining and comparing cosmic and not-cosmic multiple-hit spectra
By examining the pair-production spectra.

17. Intrinsic 137Cs Level
31.3 kg-day of CsI(Tl) data was analysed.
137Cs contamination level in CsI was drived ==> (1.55 ± 0.02 ) X g/g

18. Intrinsic U and Th Contamination Level
Data: The total of 40 crystals with data size of 1725 kg·day was analysed.
Master Thesis results of Zhu Y. F. from Tsing Hua Univ. in Beijing (2006)
ii) 212Bi(b-,64%) → 212Po(a, 299ns) → 208Pb
i) 214Bi(b-)→ 214Po(a,164ms) → 210Pb
Selection: b- pulse followed by a large a pulse
Selection: 1st pulse is g(b) shaped &
2nd pulse a shaped
T1/2 = (283 ± 37) ns. β α β α
T1/2 = (163 ±8) ms
232Th abundance = 2.3 ± 0.1 x10-12 g/g
238U abundance = 0.82 ± 0.02 x g/g
T1/2 = (0.141± 0.006) s a
iii) 220Rn(a) → 216Po(a, 0.15s) → 212Pb
Selection: two α events with time delay less than 1s
232Th abundance = 2.23 ± 0.06 x g/g

19. Efficiencies, BG Level and Measured Half-Lives
Master Thesis results of Zhu Y. F. from Tsing Hua Univ. in Beijing (2006)
Paper was sent to Nuclear Instruments and Methods in Physics Research A.

20. Background Understanding via Multi Hit
Not-Cosmic Multi-Hit Energy Spectrum
Cs-137
K -40
Tl -208

21. Individual Multi-Hit Energy Spectrum 1600-2200 keV
Cs-134 (n + 133Cs g 134Cs)
97.6% 605keV;
85.5% 796keV
Cosmic induced neutrons can be captured by the target nuclei 133Cs.
The Z-distribution shows the source is intrinsic.
605
796 

22. Individual Multi-Hit Energy Spectrum 2300 – 2800 keV (Tl-208)
Co-60 contamination
keV 99.86% accompanied with keV 99.98%
Tl Pair Production: One escape peak
(~ keV)
Sources are outside
511
1173
1332
2105 

23. Individual Multi-Hit Energy Spectrum 3000 – 4000 keV
2614 keV % accompanied with 583 keV 86%
2614 keV keV 23%
2614 keV keV keV 24%
2614 keV keV keV 4%
Combination of Tl gammas can affect up to around 4 MeV

24. Background Understanding: Cosmic-Ray Inefficiency
3-hit Peaks
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.
2-hit Peaks

25. Pair Production Approach for 4 – 8 MeV
Study on Background in Statistically 2&3 Hit and Pair Production Approaches--Preliminary
2&3 Hit Approach for 4 – 8 MeV
Two-Hit:
Expected to Single-Hit ratio:
Exp/SH = cm z-cut
= 0.96 for no z-cut
Three-Hit:
Exp/SH = 0.98 for 4cm z-cut
= 1.15 for no z-cut
Pair Production Approach for 4 – 8 MeV
For no z-cut
Exp/SH = 1.03
For 4cm z-cut
Exp/SH = 0.90

26. Improvement on Background Understanding8 4

27. Cutting at this point, suppression 68 %(.248/.727)
c 2 Analysis
Black – Recorded Pulse by FADC
Green – Reference a pulse
Red - Reference g pulse
Differenciate Single and multiple site events
Cutting at this point, suppression 68 %(.248/.727)
c-square function
Red – e- events
Black – g events
g- pulse
a- pulse

28. Preliminary Result of sin2qW
Ph.D. Thesis results of Dr. Lin Shin Ted (2006) g
The best fit of sin2qW : ± at 3-8MeV
0.30 ± at 3.5-8MeV

29. Expected Accuracy of sin2qW with data size
130

30. Expected Result of Accuracy of e-e) and sin2qWg

31. “Our aim is to measure (ee) with <20% accuracy.”
TEXONO and World status !
Characteristics of the previous and current neutrino-e scattering experiments
CsI(Tl) cry.
186 kg
3.0
1.8 (expect)
0.1
<20% (goal)
CF4 gas
21 kg
0.9
1.77
0.2
50%
Si(Li)
37.5 kg
0.6
5.2
0.008
49%
Fluorocarbon
103 kg
3.1
0.78
53%
Plastic scin.
15.9 kg
1.5
1.2
0.18
29%*
TEXONO
NUMU
Rovno
Kurtchatov
Savannah
Experiments
Target
Fiducial Mass
Thr. (MeV)
Signal Evt./Day
S / B
Accuracy of
(ee)
“Our aim is to measure (ee) with <20% accuracy.”
Our aim is to measure Sin2W value with <8% accuracy.

32. Thank you