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Detection Methods at Reactor N eutrino E xperiments

Jun Cao Institute of High Energy Physics (Beijing). Detection Methods at Reactor N eutrino E xperiments. Feb. 11-15, 2013. Outline. A better title: Liquid Scintillator Detector for High Precision (Reactor) Neutrino Studies. Reactor n eutrino experiments

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Detection Methods at Reactor N eutrino E xperiments

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  1. Jun Cao Institute of High Energy Physics (Beijing) Detection Methods at Reactor Neutrino Experiments Feb. 11-15, 2013

  2. Outline A better title: Liquid Scintillator Detector for High Precision (Reactor) Neutrino Studies. Reactor neutrino experiments Towards a high precision measurement Highlighted technologies Future reactor neutrino detector Summary

  3. Reactor Neutrino Experiments Reactor anti-neutrino experiments have played a critical role in the 60-year-long history of neutrinos. Daya Bay, Double Chooz, RENO DYBII • The first neutrino observation in 1956 by Reines and Cowan. • Determination of the upper limit of mixing angle 13in 90's (Chooz, Palo Verde) • The first observation of reactor anti-neutrino disappearance at KamLAND in 2002. • Measurement of the smallest mixing angle 13at Daya Bay and other experiments in 2012.

  4. Reactor Neutrinos • Most commercial reactors are PWR or BWR. • 235U, 239Pu, 241Pu beta spectra measured at ILL, 238U theoretically. • In LS: Energy 1-10 MeV, Rate : ~ 1 event/day/ton/GW @ 1km • Power fluctuation <1%, rate and shape precision 2-3% • Rate and spectra were verified by Bugey, Bugey3, Bugey4 • Reactor anomaly Peak at 4 MeV

  5. Non-proliferation Monitoring Bowden, LLNL, 2008 • Non-proliferation monitoring studies supported by IAEA (France, US, Russia, Japan, Brazil, Italy) • Ton-level detector, very close to core. • Water-based liquid scintillator for safety?

  6. Prompt signal Capture on H, or Gd, Cd, etc.Delayed signal The Cowan-Reines Reaction • The first observation of neutrinos in 1956 by Reines & Cowan. • Inverse beta decay in CdCl3 water solution  coincidence of prompt and delayed signal • Liquid scintillator + PMTs • Underground • Modern experiments are still quite similar, except • Loading Gd into liquid scintillator • Larger, better detector • Deeper underground, better shielding

  7. keV Scattering Experiments • Neutrino magnetic moments exp. • Texono, GEMMA (HPGe) • MUNU (TPC)

  8. CHOOZ Baseline 1.05 km 1997-1998, France 8.5 GWth 300 mwe 5 ton 0.1% Gd-LS Bad Gd-LS R=1.012.8%(stat) 2.7%(syst), sin2213<0.17 Eur. Phys. J. C27, 331 (2003)

  9. Palo Verde 1998-1999, US 11.6 GWth Segmented detector 12 ton 0.1% Gd-LS Shallow overburden 32 mwe Baseline 890m & 750m R=1.012.4%(stat) 5.3%(syst) 60%/year Palo Verde Gd-LS Chooz Gd-LS 1st year 12%, 2nd year 3% Phys.Rev.D64, 112001(2001)

  10. KamLAND 2002-, Japan 53 reactors, 80 GWth 1000 tonLS 2700 mwe Radioactivity  fiducial cut, Energy threshold Baseline 180 km

  11. Measuring 13 23 ~ 45 Atmospheric Accelerator 13 = ? Reactor Accelerator 12 ~ 34 Solar Reactor 0 Precision Measurement at reactors sin2213~0.04 Fogli et al., hep-ph/0506307

  12. Precision Measurement at Reactors Major sources of uncertainties: • Reactor related ~2% • Detector related ~2% • Background 1~3% Lessons from past experience: • CHOOZ: Good Gd-LS • Palo Verde: Better shielding • KamLAND: No fiducial cut Near-far relative measurement Mikaelyan and Sinev, hep-ex/9908047

  13. The Daya Bay Experiment • 6 reactor cores, 17.4 GWth • Relative measurement • 2 near sites, 1 far site • Multiple detector modules • Good cosmic shielding • 250 m.w.e@ near sites • 860 m.w.e @ far site • Redundancy 3km tunnel

  14. Daya Bay Results 2011-11-5 Mar.8, 2012, with 55 day data sin2213=0.0920.016(stat)0.005(syst) 5.2 σ for non-zero θ13 2011-12-24 2011-8-15 Jun.4, 2012, with 139 day data sin2213=0.0890.010(stat)0.005(syst) 7.7 σ for non-zero θ13

  15. Double Chooz Daya Bay Double Chooz

  16. Double Chooz Results sin22q13=0.0860.041(Stat)0.030(Syst), 1.7σ for non-zero θ13 sin22q13=0.1090.030(Stat)0.025(Syst), 2.9σfor non-zero θ13 Far detector starts data taking at the beginning of 2011 First results in Nov. 2011 based on 85.6 days of data Updated results on Jun.4, 2012, based on 228 days of data

  17. RENO Daya Bay 6 cores 16.5 GW 16t, 120 MWE RENO Double Chooz 16t, 450 MWE

  18. RENO sin22q13=0.1130.013(Stat)0.019(Syst), 4. 9σ for non-zero θ13 Data taking started on Aug. 11, 2011 First physics results based on 228 days data taking (up to Mar. 25, 2012) released on April 3, 2012, revised on April 8, 2012:

  19. Rate and Spectrum sin22θ13=0.089±0.010(stat)±0.005(syst) R = 0.944 ± 0.007 (stat) ± 0.003 (syst) Still dominated by statistics Chinese Physics C, Vol. 37, No. 1 (2013) 011001

  20. Global Picture of 13 Measurements Time line

  21. Prompt signal Delayed signal, Capture on H (2.2 MeV) or Gd (8 MeV), ~30s Detecting Reactor Antineutrino Inverse beta decay Peak at ~4 MeV 0.1% Gd by weight Energy selection, time correlation Major backgrounds: • Cosmogenic neutron/isotopes • 8He/9Li • fast neutron • Ambient radioactivity • accidental coincidence Capture on H Capture on Gd

  22. Detector Design Water • Shield radioactivity and cosmogenic neutron • Cherekov detector for muon RPC or Plastic scintillator • muon veto Three-zone neutrino detector • Target: Gd-loaded LS • 8-20 t for neutrino • -catcher: normal LS • 20-30 t for energy containment • Buffer shielding: oil • 40-90 t for shielding

  23. Detector Design Water • Shield radioactivity and cosmogenic neutron • Cherekov detector for muon RPC or Plastic scintillator • muon veto Three-zone neutrino detector • Target: Gd-loaded LS • 8-20 t for neutrino • -catcher: normal LS • 20-30 t for energy containment • Buffer shielding: oil • 40-90 t for shielding Daya Bay Reflective panels Reduce PMT numbers to 1/2

  24. Prompt signal Delayed signal, Capture on H (2.2 MeV) or Gd (8 MeV), ~30s Gadolinium-doped Liquid Scintillator Natural Radioactivity Singles Spectrum • Significantly Lower the low-background requirement • Well-defined target mass(no fiducial volume cut) • KamLAND didn't dope; DYB-II will not dope. • w/o doping, DYB 20 t detector 5m, 110 t --> 6.5m, 210 t; lower eff. due to muon veto; larger uncer. nH, 2.2 MeV nGd, 8.05 MeV Coincidence pair in (1-200) s

  25. Why 3-layer w/ -catcher w/o -catcher • Inner Gd-LS: precise target mass, E higher than radioact. • Middle layer: -catcher to contain gamma energy • attenuation length of 1 MeV  ~ 20 cm • neutron selection eff increase from 0.2% to 0.4% for 2-layer • Energy resolution is NOT sensitive (7% 12%) • Outer layer: shield radioactivity, uniform response. • Uncertainty from accidental backgrounds (DYB) ~0.05%

  26. Functional Identical Detectors • "Same batch" of liquid scintillator 5x40 t Gd-LS, circulated 20 t filling tank 200 t LS, circulated 4-m AV in pairs Assembly in pairs • Idea of "identical detectors" throughout the procedures of design / fabrication / assembly / filling. • For example: Inner Acrylic Vessel, designed D=31205 mm • Variation of D by geometry survey=1.7mm, Var. of volume: 0.17% • Target mass var. by load cell measurement during filling: 0.19%

  27. Side-by-side Comparison (1) Two ADs in EH1 nGd 8 MeV peak within 0.5% AD spectra Energy scale of 6 ADs n capture time Relative uncertainties: difference between detectors

  28. The State-of-the-art Neutrino Detector Can be improved w/ det. by det. correction Can be further constrained w/ more data • Designed detector uncertainties (relative) • Daya Bay 0.15-0.38%, Double Chooz 0.5%, RENO 0.5% • Comparing to 2.7% of CHOOZ • Achieved 0.2% in short term

  29. Side-by-side Comparison (2) Neutrino Enery spectra Data set: 2011.9 to 2012.5 This check shows that syst. are under control, and will eventually "measure" the total syst. error • Expected ratio of neutrino events: R(AD1/AD2) = 0.982 • The ratio is not 1 because of target mass, baseline, etc. • Measured ratio: 0.987  0.004(stat.)  0.003(syst.)

  30. Previous Gd-LS 60%/y 3%/y Palo Verde Gd-LS GdCl3+EHA (carboxylic acid) Chooz Gd-LS Gd(NO3)3 + hexanol • Solvent: Xylene, Pseudocumene, ... attack acylic (+MO) • New solvents of high flash point, low toxicity ... • LAB, PXE, DIN, PCH Doping metal into organic LS is not easy.

  31. Gd-LS fluor: PPO, second wavelenth shifter: bis-MSB • Systematic studies on Gd-LS after the failure of CHOOZ. • β-diketones: Acac, DBM, BTFA, HPMBP, THD • Carboxylic acid: 2-MVA(6C), n-heptanoic(7C), EHA(8C), TMHA(9C) • Organophosphorous: TOPO, D2EHP, TEP, DBBP • Stability, solubility, transparency and purification, large-scale production ...

  32. Gd-LS Production in DYB GdCl3 purification GdCl3 Wet solid PH tuned TMHA Gd(TMHA)3 synthesis and dissolution Fluor-LAB Clear Gd(TMHA) in LAB ~ 0.5% concentration 4 ton Mixing N2 bubbling 5x40t Gd-LS tanks To 40ton Tank filtration

  33. Radiopurification of GdCl3  • 232Th228Ra228Th224Ra212Bi212Po(164s) • 238U234Th234U230Th226Ra214Bi214Po(0.3s)210Pb210Po • 235U231Pa227Ac219Rn215Po(1.78ms) (1ms, 3ms) 238U Chin. Phys. C37, 011001 (2013) 232Th: 10 mBq/ton (2.5e-3 ppb) 238U: 0.5 mBq/ton (4e-5 ppb) 227Ac: 10 mBq/ton (10ms, 160ms) 232Th 227Ac Prompt energy (MeV) Total (1ms, 2ms) Natural abundance 238U/235U ~ 22 In DYB Gd-LS: 238U/235U ~ 0.05 Purification of at least 400 times (some are duringrefining of Gd) 227Ac Delayed energy (MeV) Co-precipitation to remove U/Th: increase the PH of GdCl3 water solution (~5% precipitate), filter, and tune back. Complexing to remove Ra

  34. Calibration ACU-B ACU-A ACU-C • Daya Bay: weekly calibration • ACU (enable >99.7% μ eff.): LED, Ge, Co, 241Am-13C (0.5 Hz) • Special ACU: Cs, Mn, Am-Be • Manual (4π): Co, 238Pu-13C (4% 6 MeV gamma) • Double Chooz: laser, Cs, Ge, Co, Cf • RENO: LED, Cs, Ge, Co, Cf • Relative energy scale uncertainty within 0.5%

  35. 1cmAcrylic sheet 1cm Acrylic sheet Reflective Panels 4.5 m in diameter 2 cm thick bulk polymerization Epoxy sealing 65 m ESR ESR film: Specular reflection for better understanding of detector Sandwich structure, keep intact surface with vacuum pressure Electrostatic adherence to ensure a perfect specular surface.

  36. Reflective Panel in Detector

  37. Next Step: DayaBay-II Experiment DYB-II has been approved in China in Feb. 2013 Equivalent to CD1 of US DOE Daya Bay Daya Bay II • 20 kton LS detector • 3%/E̅resolution • Rich physics • Mass hierarchy • Precision measurement of 4 oscillation parameters to <1% • Supernovae neutrino • Geoneutrino • Sterile neutrino • Atmospheric neutrinos • Exotic searches Talk by Y.F. Wang at ICFA seminar 2008...NuFact 2012; by J. Cao at Nutel 2009...NPB 2012 (ShenZhen); Paper by L. Zhan, Y.F. Wang, J. Cao, L.J. Wen, PRD78:111103,2008; PRD79:073007,2009

  38. The reactors and possible sites Lufeng Huizhou Kaipin, Jiangmeng, Guang Dong Daya Bay Hong Kong Taishan Yangjiang

  39. Detector Concept Muon tracking Stainless Steel Tank Water Seal Liquid Scintillator20 kt Water Buffer 10kt Acrylic sphere：φ34.5m Oil buffer 6kt SS sphere ： φ37 .5m ~15000 20” PMTsoptical coverage: 70-80% VETO PMTs • Traditional Design (figure) • Alternate: acrylic -> ballon • Alternate: acrylic -> PET sphere 2) No SST (like SNO) 3) Only SST, no inner vessel 4) Modulized oil box in SST

  40. DYB-II Energy Resolution Uniformly Distributed Events R3 After vertex-dep. correction , or (2.6/ • DYB-II MC, based on DYB MC (p.e. tuned to data), except • DYBII Geometry and 80% photocathode coverage • SBA PMT: maxQE from 25% -> 35% • Lower detector temperature to 4 degree (+13% light) • LS attenuation length (1 m-tube measurement@430 nm) • from 15 m = absoption 24 m + Raylay scattering 40 m • to 20 m = absorption 40 m + Raylay scattering 40 m

  41. Discovery Power Taking into account Dm232from T2Kand Nova in the future： Contribution from absolute Dm232 measurement Will be more precise than CKM matrix elements ! Probing the unitarity of UPMNS to ~1% level If m232at 1%precision，mass hierarchy could be determined to ~5in 6 years. (core distribution and energy non-linearity may degrade it a little bit.

  42. Technical Challenges • 15000 20-inPMTs with maxQE  35% • MCP-based PMT, led by IHEP, since 2008. • Hamamatsu dynode PMTs (or HPD-based) • LAPPDs, Borosilicate capillary array for MCP, U. Chicago, ANL, etc. • Ultra-transparent liquid scintillator • Default recipe: LAB + PPO + bis-MSB (Daya Bay undoped LS) • High transparence LAB • Purification of LS • Mechanics of the giant detector • Energy calibration

  43. DYBII: Brief schedule Welcome collaborators Civil preparation：2013-2014 Civil construction：2014-2017 Detector R&D：2013-2016 Detector component production：2016-2017 PMT production：2016-2019 Detector assembly & installation：2018-2019 Filling & data taking：2020

  44. Mass Hierachy • Solar neutrino • Geoneutrino • Supernovae • T2K beam • exotic S.B. Kim, talk at Neutrino 2012

  45. Summary • Reactor Neutrino experiments were prosperous. • Liquid scintillator + PMTs • Detector uncertainties reduced from ~3% to 0.2% in recent q13 measurements. • As the most powerful man-made neutrino source, reactor neutrinos will continue to contribute in • Mass hierarchy • Precision measurement of mixing parameters to < 1%  unitarity test of the mixing matrix • Sterile neutrinos, Neutrino magnetic moments, ... • Challenges: Liquid scintillator, PMTs, Gaint detector

  46. In 2013: Feb. 3 Kitchen God Festival Feb. 10 Chinese New Year Feb. 24 The Lantern Festival Happy New Year !

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