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 e e 2 e p e n
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 Cosmogenic neutron/isotopes 8He/9Li 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 e e 2 e p e n
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'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. 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. Complexing to remove Ra • 232Th228Ra228Th224Ra212Bi212Po(164s)
• 238U234Th234U230Th226Ra214Bi214Po(0.3s)210Pb210Po • 235U231Pa227Ac219Rn215Po(1.78ms) Chin. Phys. C37, 011001 (2013) (1s, 3s) 232Th: 10 mBq/ton (2.5e-3 ppb) 238U
238U: 0.5 mBq/ton (4e-5 ppb) 227Ac: 10 mBq/ton 232Th (10 s, 160 s) 227Ac
Natural abundance 238U/235U ~ 22 In DYB Gd-LS: 238U/235U ~ 0.05 (1ms, 2ms) Total
(MeV) energy Prompt Purification of at least 400 times 227Ac (some are during refining of Gd)
Delayed energy (MeV) 33 Calibration 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%
ACU-B ACU-A ACU-C
34 Reflective Panels 4.5 m in diameter ESR2 film: cm thick Specular reflection for better understanding of detector Sandwich structure, keep intact surface with vacuum pressure Electrostatic adherence to ensure a perfect specular surface.
bulk polymerization Epoxy sealing 65 m ESR 1cm Acrylic sheet
1cm Acrylic sheet
PMT Covera pe yield pe yield ge (pe/MeV) /Coverage Daya Bay 192 8" ~6% 163 1.77 RENO 354 10" ~15% 230 1 Double Chooz 390 10" ~16% 200 0.81 35 Reflective Panel in Detector
36 Next Step: Daya Bay-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%/E̅ resolution 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 37 The reactors and possible sites
Daya Bay Huizhou Lufeng Yangjiang Taishan Status Operational Planned Planned Under construction Under construction Power 17.4 GW 17.4 GW 17.4 GW 17.4 GW 18.4 GW
Lufeng Kaipin, Jiangmeng, Huizhou Guang Dong Daya Bay
Hong Kong
Taishan
Yangjiang 38 Detector Concept Muon tracking
Stainless Steel Tank
Water Seal Liquid Scintillator 20 kt Water Buffer 10kt Acrylic sphere：φ34.5m Oil buffer 6kt ~15000 20” PMTs SS sphere ： φ 37 .5m optical coverage: 70-80%
VETO PMTs
1) Traditional Design (figure) 2) No SST (like SNO) • Alternate: acrylic -> ballon 3) Only SST, no inner vessel • Alternate: acrylic -> PET sphere 4) Modulized oil box in SST 39 DYB -II Energy Resolution 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
Uniformly Distributed Events
R3
After vertex-dep. correction ퟑ. ퟎ%/ 푬, or (2.6/ 푬 + ퟎ. ퟑ)% 40 Discovery Power 2 Taking into account m 32 from T2K and Nova in the future：
Current DYB II 2 m 12 3% 0.6% 2 m 23 5% 0.6% 2 sin 12 6% 0.7% Contribution from sin2 20% N/A 2 23 absolute m 32 2 measurement sin 13 14% 4% ~ 15%
Will be more precise than CKM 2 matrix elements ! If m 32 at 1% precision，mass hierarchy could be determined to ~5 in 6 years. (core distribution Probing the unitarity of UPMNS to and energy non-linearity may ~1% level degrade it a little bit.
41 Technical Challenges
15000 20-in PMTs 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
42 DYBII: Brief schedule
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
Welcome collaborators
43
• Mass Hierachy • Solar neutrino • Geoneutrino • Supernovae • T2K beam • exotic
S.B. Kim, talk at Neutrino 2012 44 Summary
Reactor Neutrino experiments were prosperous. Liquid scintillator + PMTs Detector uncertainties reduced from ~3% to 0.2% in
recent 13 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
45 Happy New Year !
In 2013: Feb. 3 Kitchen God Festival Feb. 10 Chinese New Year Feb. 24 The Lantern Festival