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Study of Neutrino-Electron Scattering with a Fine-Grained CsI(Tl) Scintillating Crystal Detector

This study aims to measure the neutrino-electron scattering cross-section using a fine-grained CsI(Tl) scintillating crystal detector. The research includes data analysis techniques, background suppression, and understanding of radioactive contaminants and environmental backgrounds.

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Study of Neutrino-Electron Scattering with a Fine-Grained CsI(Tl) Scintillating Crystal Detector

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  1. Study of Neutrino-Electron Scattering with a Fine-Grained CsI(Tl) Scintillating Crystal Detector Muhammed Deniz1,21: METU, Ankara, Turkey2: 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 NEUTRINO INTERACTIONS ON CsI(Tl) For (e-e), both NC & CC and their interference term contribute e + e-e+ e- Reactor : high flux of low energy (MeV range) electron anti-neutrinos.

  6. TEXONO Physics Program on CsI(Tl) detector e + e-e+ e- CsI(Tl) (186 kg) : • attempt a measurement of Standard Model (ee-) sinw at MeV range 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 eN(MM) HPGe: Mass: 1kg Detection Threshold: 5keV Background: 1 kg-1keV-1day-1 @12-60 keV MM: µνe <1.3x10-10µB at 90% CL eN(SM) ee-(MM) ee-(SM) SM (e) > 3 MeV MM (e) 1-100 keV Coh. (N) < 1 keV Phys. Rev. Lett. 90, 131802 (2003)

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

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

  10. CsI(Tl) Array : Highlights • Period IIData Volume : Total ~ 110 / 50 days ON/OFF • 186 kg mass;20+20 and40 cmlength(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

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

  13. Data Analysis Techniques - Defining Cuts Veto cut: Reject Cosmic raySingle-hit cut: Anti Compton effectPSD cut : Alpha particleZ-pos cut : Both veto and S.H. effect

  14. 137Cs (662 keV) 40K (1460 keV) 208Tl (2614keV) ON and OFF Energy Spectra OFF spectrum in all energy range ON&OFF spectra in 3-8 MeV energy range 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

  15. Two Type : • Radioactive Contaminants [Decays of radioactive contaminants mainly232Th and238Uchainproduce background in the region of interest. 137Cs, 40K ,and60Coare in lower energy side but208Tlcan affect. • Estimate the abundance of 137Cs,238U and 232Th inside the detector. • Figure out the contribution of 238U and 232Thchains 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

  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 backgroundin 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 • REALIZATION: • By examining and comparingcosmic 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 10-17 g/g

  18. T1/2 = (283 ± 37) ns. T1/2 = (163 ±8) ms α β α a a β T1/2 = (0.141± 0.006) s Intrinsic U and ThContamination Level Data:The total of 40 crystals with data size of 1725 kg·day was analysed. Master Thesis results of Zhu Y. F. fromTsing 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 232Th abundance = 2.3 ± 0.1 x10-12 g/g 238U abundance = 0.82 ± 0.02 x10-12 g/g iii) 220Rn(a) → 216Po(a, 0.15s) → 212Pb Selection:twoα events with time delay less than 1s 232Th abundance = 2.23 ± 0.06 x 10-12g/g

  19. Efficiencies, BG Level and Measured Half-Lives Master Thesis results of Zhu Y. F. fromTsing 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 g134Cs) • 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. 511 1173 1332 2105 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 

  23. 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

  24. 3-hit Peaks 2-hit Peaks Background Understanding: Cosmic-Ray Inefficiency • To understand the contribution of cosmic rays to the background, ~ 926kg*day data was analyzed for cosmic and not-cosmic multi-hit as well as pair production.

  25. Study on Background in Statistically 2&3 Hit and Pair Production Approaches--Preliminary

  26. Improvement on Background Understanding g 8 4

  27. Red – e- events Black – g events a- pulse g- pulse Cutting at this point, suppression 68 %(.248/.727) c-square function c2Analysis Black –Recorded Pulse by FADC Green – Reference a pulse Red - Referenceg pulse Differenciate Single and multiple site events

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

  29. Expected Accuracy of sin2qWwith data size 130

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

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

  32. Thank you

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