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

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.

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

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

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-

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)

TEXONO Program on Neutrino Interaction Cross- Sections Phys. Rev. Lett. 90, 131802 (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) 1-100 keV ee- (SM) SM (e) > 3 MeV

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

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

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

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

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 40 cm

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

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 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

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.

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.

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 10-17 g/g

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 x10-12 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 10-12 g/g

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.

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

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 

Individual Multi-Hit Energy Spectrum 2300 – 2800 keV (Tl-208) Co-60 contamination 1173.2 keV 99.86% accompanied with 1332.5 keV 99.98% Tl Pair Production: One escape peak (~ 2105 + 511 keV) Sources are outside 511 1173 1332 2105 

Individual Multi-Hit Energy Spectrum 3000 – 4000 keV 2614 keV 99.79 % accompanied with 583 keV 86% 2614 keV + 860 keV 23% 2614 keV + 580 keV + 510 keV 24% 2614 keV + 760 keV + 580 keV 4% Combination of Tl gammas can affect up to around 4 MeV

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

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 = 0.82 4cm 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

Improvement on Background Understanding 8 4

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

Preliminary Result of sin2qW Ph.D. Thesis results of Dr. Lin Shin Ted (2006) g The best fit of sin2qW : 0.37 ± 0.13 at 3-8MeV 0.30 ± 0.22 at 3.5-8MeV

Expected Accuracy of sin2qW with data size 130

Expected Result of Accuracy of e-e) and sin2qW g

“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.

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