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Detection Methods at Reactor Neutrino Experiments Jun Cao

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Detection Methods at Reactor Neutrino Experiments Jun Cao Detection Methods at Reactor Neutrino Experiments Jun Cao Institute of High Energy Physics (Beijing) Feb. 11-15, 2013 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 2 Reactor Neutrino Experiments Reactor anti-neutrino experiments have played a critical role in the 60-year-long history of neutrinos. Daya Bay, The first neutrino observation in Double Chooz, RENO DYBII 1956 by Reines and Cowan. Determination of the upper limit of mixing angle 13 in 90's (Chooz, Palo Verde) The first observation of reactor anti-neutrino disappearance at KamLAND in 2002. Measurement of the smallest mixing angle 13 at Daya Bay and other experiments in 2012. 3 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 4 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? 5 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 Prompt signal e e 2 e p e n Capture on H, or Gd, Cd, etc. Delayed signal 6 keV Scattering Experiments Neutrino magnetic moments exp. Texono, GEMMA (HPGe) MUNU (TPC) 7 CHOOZ Baseline 1.05 km 1997-1998, France 8.5 GWth 300 mwe 5 ton 0.1% Gd-LS Bad Gd-LS 2 R=1.012.8%(stat) 2.7%(syst), sin 213<0.17 Parameter Relative error Reaction cross section 1.9 % Number of protons 0.8 % Detection efficiency 1.5 % Reactor power 0.7 % Energy released per fission 0.6 % Combined 2.7 % Eur. Phys. J. C27, 331 (2003) 8 Palo Verde 1998-1999, US 11.6 GWth Segmented detector 12 ton 0.1% Gd-LS Shallow overburden 32 mwe Baseline 890m & 750m R=1.012.4%(stat) 5.3%(syst) 60%/year Palo Verde Gd-LS Chooz Gd-LS 1st year 12%, 2nd year 3% Phys.Rev.D64, 112001(2001) 9 KamLAND Baseline 180 km 2002-, Japan 53 reactors, 80 GWth 1000 ton LS 2700 mwe Radioactivity fiducial cut, Energy threshold 10 Measuring 13 i 1 00c13 0 s 13 c12 s 12 0 e 00 i i Ue 0 c s 00e s c 0 00 23 23 12 12 0 s23 c 23 s13 0 c 13 0 0 10 0 1 ~ 45 ~ 34 23 13 = ? 12 Atmospheric Reactor Solar 0 Accelerator Accelerator Reactor Precision Measurement at reactors 2 sin 213~0.04 Fogli et al., hep-ph/0506307 11 Precision Measurement at Reactors Major sources of uncertainties: Lessons from past experience: Reactor related ~2% CHOOZ: Good Gd-LS Detector related ~2% Palo Verde: Better shielding Background 1~3% KamLAND: No fiducial cut Near-far relative measurement Mikaelyan and Sinev, hep-ex/9908047 Parameter Error Near-far Reactor ν flux 1.9 % 0 Energy released per fission 0.6 % 0 Reactor power 0.7 % ~0.1% Number of protons 0.8 % < 0.3% Detection efficiency 1.5 % 0.2~0.6% CHOOZ Combined 2.7 % < 0.6% 12 The Daya Bay Experiment • 6 reactor cores, 17.4 GWth • Relative measurement – 2 near sites, 1 far site • Multiple detector modules • Good cosmic shielding 3km tunnel – 250 m.w.e @ near sites – 860 m.w.e @ far site • Redundancy 13 Daya Bay Results 2011-11-5 Mar.8, 2012, with 55 day data 2 sin 213=0.0920.016(stat)0.005(syst) 5.2 σ for non-zero θ13 2011-12-24 2011-8-15 Jun.4, 2012, with 139 day data 2 sin 213=0.0890.010(stat)0.005(syst) 7.7 σ for non-zero θ13 14 Double Chooz Daya Bay Double Chooz 15 Double Chooz Results Far detector starts data taking at the beginning of 2011 First results in Nov. 2011 based on 85.6 days of data 2 sin 213=0.0860.041(Stat)0.030(Syst), 1.7σ for non-zero θ13 Updated results on Jun.4, 2012, based on 228 days of data 2 sin 213=0.1090.030(Stat)0.025(Syst), 2.9σ for non-zero θ13 16 RENO 6 cores 16t, 120 MWE 16.5 GW Daya Bay RENO Double Chooz 16t, 450 MWE 17 RENO 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: 2 sin 213=0.1130.013(Stat)0.019(Syst), 4. 9σ for non-zero θ13 18 Rate and Spectrum 2 sin 2θ13=0.089±0.010(stat)±0.005(syst) R = 0.944 ± 0.007 (stat) ± 0.003 (syst) EH1 140 000 events EH2 66 000 events Still dominated by statistics EH3 30 000 events Chinese Physics C, Vol. 37, No. 1 (2013) 011001 19 Global Picture of 13 Measurements Time lineTime 20 Detecting Reactor Antineutrino Inverse beta decay Prompt signal Peak at ~4 MeV Delayed signal, Capture on H (2.2 MeV) or Gd (8 MeV), ~30s 0.1% Gd by weight Energy selection, time correlation Major backgrounds: Capture on H e e 2 Cosmogenic neutron/isotopes 8He/9Li e p e n Capture on Gd fast neutron Ambient radioactivity accidental coincidence 21 Detector Design Water RPC or Plastic scintillator Shield radioactivity and muon veto cosmogenic neutron Cherekov detector for muon 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 ( ton ) DYB DC RENO Target 20 8.3 16 -catcher 20 18 28 Buffer 37 88 65 Total 77 114 110 22 Detector Design Water RPC or Plastic scintillator Shield radioactivity and muon veto cosmogenic neutron Cherekov detector for muon 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 23 Gadolinium -doped Liquid Scintillator Natural Radioactivity Prompt signal Delayed signal, Capture on H Singles Spectrum (2.2 MeV) or Gd (8 MeV), ~30s nH, 2.2 MeV nGd, 8.05 MeV Significantly Lower the low- background requirement Well-defined target mass(no fiducial volume cut) KamLAND didn'te dope;e DYB2-II will not dope. e p e n w/o doping, DYB 20 t detector 5m, 110 t --> 6.5m, 210 t; lower eff. due to muon veto; larger uncer. Coincidence pair in (1-200) s 24 Why 3-layer 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%) w/ -catcher w/o -catcher Outer layer: shield radioactivity, uniform response. Uncertainty from accidental backgrounds (DYB) ~0.05% 25 Functional Identical Detectors Idea of "identical detectors" throughout the procedures of design / fabrication / assembly / filling. For example: Inner Acrylic Vessel, designed D=31205 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% Diameter IAV1 IAV2 IAV3 IAV4 IAV5 IAV6 Surveyed(mm) 3123.12 3121.71 3121.77 3119.65 3125.11 3121.56 Variation (mm) 1.3 2.0 2.3 1.8 1.5 2.3 "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 26 Side -by-side Comparison (1) Relative uncertainties: difference between detectors Two ADs in EH1 nGd 8 MeV peak within 0.5% Energy scale of 6 ADs n capture time AD spectra 27 The State -of-the-art Neutrino Detector 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 Can be improved w/ det. by det. correction Can be further constrained w/ more data 28 Side -by-side Comparison (2) 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.) 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 29 Previous Gd-LS Doping metal into organic LS is not easy. 60%/y 3%/y Chooz Gd-LS Palo Verde Gd-LS GdCl +EHA (carboxylic acid) Gd(NO3)3 + hexanol 3 Solvent: Xylene, Pseudocumene, ... attack acylic (+MO) New solvents of high flash point, low toxicity ... LAB, PXE, DIN, PCH 30 Gd-LS 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 ... Exp. Solvent Gd Agent Quantity (t) CHOOZ IPB Hexanol 5 Palo Verde PC+MO EHA 12 Double Chooz PXE+dodecane -dikotonates 8 Daya Bay LAB TMHA 185 fluor: PPO, second wavelenth shifter: bis-MSB 31 Gd-LS Production in DYB GdCl3 GdCl3 purification 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 32 Radiopurification of GdCl3 Co-precipitation to remove U/Th: increase the PH of GdCl3 water solution (~5% precipitate), filter, and tune back.
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