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. u u u 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. u The first neutrino observation in 1956 by Reines and Cowan. u Determination of the upper limit of mixing angle 13 in 90's (Chooz, Palo Verde) u The first observation of reactor anti -neutrino disappearance at Kam. LAND in 2002. u Measurement of the smallest mixing angle 13 at Daya Bay and other experiments in 2012. Daya Bay, Double Chooz, RENO DYBII 3

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

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

The Cowan-Reines Reaction u The first observation of neutrinos in 1956 by Reines & Cowan. ð Inverse beta decay in Cd. Cl 3 water solution coincidence of prompt and delayed signal ð Liquid scintillator + PMTs ð Underground u Modern experiments are still quite similar, except ð Loading Gd into liquid scintillator ð Larger, better detector ð Deeper underground, better shielding Prompt signal Capture on H, or Gd, Cd, etc. Delayed signal 6

ke. V Scattering Experiments u Neutrino magnetic moments exp. ð Texono, GEMMA (HPGe) ð 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 R=1. 01 2. 8%(stat) 2. 7%(syst), sin 22 13<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. C 27, 331 (2003) 8

Palo Verde 1998 -1999, US 11. 6 GWth Segmented detector 12 ton 0. 1% Gd-LS Shallow overburden 32 mwe Baseline 890 m & 750 m R=1. 01 2. 4%(stat) 5. 3%(syst) 60%/year Chooz Gd-LS Palo Verde Gd-LS 1 st year 12%, 2 nd year 3% Phys. Rev. D 64, 112001(2001) 9

Kam. LAND Baseline 180 km 2002 -, Japan 53 reactors, 80 GWth 1000 ton LS 2700 mwe Radioactivity fiducial cut, Energy threshold 10

Measuring 13 23 ~ 45 Atmospheric Accelerator 13 = ? Reactor Accelerator 12 ~ 34 Solar Reactor 0 Precision Measurement at reactors sin 22 13~0. 04 Fogli et al. , hep-ph/0506307 11

Precision Measurement at Reactors Major sources of uncertainties: u Reactor related ~2% u Detector related ~2% u Background 1~3% Lessons from past experience: u CHOOZ: Good Gd-LS u Palo Verde: Better shielding u Kam. LAND: 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 – 250 m. w. e @ near sites – 860 m. w. e @ far site • Redundancy 3 km tunnel 13

Daya Bay Results 2011 -11 -5 Mar. 8, 2012, with 55 day data sin 22 13=0. 092 0. 016(stat) 0. 005(syst) 5. 2 σ for non-zero θ 13 2011 -12 -24 2011 -8 -15 Jun. 4, 2012, with 139 day data sin 22 13=0. 089 0. 010(stat) 0. 005(syst) 7. 7 σ for non-zero θ 13 14

Double Chooz Daya Bay Double Chooz 15

Double Chooz Results Far detector starts data taking at the beginning of 2011 u First results in Nov. 2011 based on 85. 6 days of data sin 22 13=0. 086 0. 041(Stat) 0. 030(Syst), 1. 7σ for non-zero θ 13 u Updated results on Jun. 4, 2012, based on 228 days of data u sin 22 13=0. 109 0. 030(Stat) 0. 025(Syst), 2. 9σ for non-zero θ 13 16

RENO 16 t, 120 MWE 6 cores 16. 5 GW Daya Bay RENO Double Chooz 16 t, 450 MWE 17

RENO u u 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: sin 22 13=0. 113 0. 013(Stat) 0. 019(Syst), 4. 9σ for non-zero θ 13 18

Rate and Spectrum sin 22θ 13=0. 089± 0. 010(stat)± 0. 005(sys R = 0. 944 ± 0. 007 (stat) ± 0. 003 t) (syst) EH 1 140 000 events EH 2 66 000 events EH 3 30 000 events Chinese Physics C, Vol. 37, No. 1 (2013) 011001 Still dominated by statistics 19

Time line Global Picture of 13 Measurements 20

Detecting Reactor Antineutrino Inverse beta decay Prompt signal Peak at ~4 Me. V Delayed signal, Capture on H (2. 2 Me. V) or Gd (8 Me. V), ~30 s 0. 1% Gd by weight Capture on H Capture on Gd Energy selection, time correlation Major backgrounds: u Cosmogenic neutron/isotopes ð 8 He/9 Li ð fast neutron u Ambient radioactivity ð accidental coincidence 21

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

Gadolinium-doped Liquid Scintillator Natural Radioactivity Singles Spectrum Prompt signal Delayed signal, Capture on H (2. 2 Me. V) or Gd (8 Me. V), ~30 s n. H, 2. 2 Me. V u u Significantly Lower the lowbackground requirement Well-defined target mass(no fiducial volume cut) Kam. LAND didn't dope; DYB-II will not dope. w/o doping, DYB 20 t detector 5 m, 110 t --> 6. 5 m, 210 t; lower eff. due to muon veto; larger uncer. n. Gd, 8. 05 Me. V Coincidence pair in (1 -200) s 24

Why 3 -layer u u Inner Gd-LS: precise target mass, E higher than radioact. Middle layer: -catcher to contain gamma energy ð attenuation length of 1 Me. V ~ 20 cm ð neutron selection eff increase from 0. 2% to 0. 4% for 2 -layer ð Energy resolution is NOT sensitive (7% 12%) w/ -catcher u w/o -catcher Outer layer: shield radioactivity, uniform response. ð Uncertainty from accidental backgrounds (DYB) ~0. 05% 25

Functional Identical Detectors u u Idea of "identical detectors" throughout the procedures of design / fabrication / assembly / filling. For example: Inner Acrylic Vessel, designed D=3120 5 mm ð Variation of D by geometry survey=1. 7 mm, Var. of volume: 0. 17% ð Target mass var. by load cell measurement during filling: 0. 19% Diameter IAV 1 IAV 2 IAV 3 IAV 4 IAV 5 IAV 6 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 ð "Same batch" of liquid scintillator 5 x 40 t Gd-LS, circulated 20 t filling tank 4 -m AV in pairs Assembly in pairs 200 t LS, circulated 26

Side-by-side Comparison (1) u Relative uncertainties: difference between detectors Two ADs in EH 1 n. Gd 8 Me. V peak within 0. 5% Energy scale of 6 ADs n capture time AD spectra 27

The State-of-the-art Neutrino Detector u u Designed detector uncertainties (relative) ð Daya Bay 0. 15 -0. 38%, Double Chooz 0. 5%, RENO 0. 5% ð 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) u u Expected ratio of neutrino events: R(AD 1/AD 2) = 0. 982 ð 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 u Doping metal into organic LS is not easy. 60%/y Chooz Gd-LS Gd(NO 3)3 + hexanol u u 3%/y Palo Verde Gd-LS Gd. Cl 3+EHA (carboxylic acid) Solvent: Xylene, Pseudocumene, . . . attack acylic (+MO) New solvents of high flash point, low toxicity. . . ð LAB, PXE, DIN, PCH 30

Gd-LS u u Systematic studies on Gd-LS after the failure of CHOOZ. ð β-diketones: Acac, DBM, BTFA, HPMBP, THD ð Carboxylic acid: 2 -MVA(6 C), n-heptanoic(7 C), EHA(8 C), TMHA(9 C) ð Organophosphorous: TOPO, D 2 EHP, TEP, DBBP Stability, solubility, transparency and purification, largescale production. . . Exp. Solvent Gd Agent Quantity (t) CHOOZ IPB Hexanol 5 Palo Verde PC+MO EHA 12 Double Chooz PXE+dodecane -dikotonates Daya Bay LAB TMHA fluor: PPO, second wavelenth shifter: bis-MSB 8 185 31

Gd-LS Production in DYB Gd. Cl 3 Wet solid Gd. Cl 3 purification PH tuned TMHA Gd(TMHA)3 synthesis and dissolution Fluor-LAB 4 ton Mixing N 2 bubbling To 40 ton Tank filtration Clear Gd(TMHA) in LAB ~ 0. 5% concentration 5 x 40 t Gd-LS tanks 32

Radiopurification of Gd. Cl 3 Co-precipitation to remove U/Th: increase the PH of Gd. Cl 3 water solution (~5% precipitate), filter, and tune back. Complexing to remove Ra u u • 232 Th 228 Ra 228 Th 224 Ra 212 Bi 212 Po(164 s) • 238 U 234 Th 234 U 230 Th 226 Ra 214 Bi 214 Po(0. 3 s) 210 Pb 210 Po • 235 U 231 Pa 227 Ac 219 Rn 215 Po(1. 78 ms) Chin. Phys. C 37, 011001 (2013) (1 s, 3 s) 238 U: 0. 5 m. Bq/ton (4 e-5 ppb) 227 Ac: 10 m. Bq/ton Natural abundance 238 U/235 U ~ 22 In DYB Gd-LS: 238 U/235 U ~ 0. 05 Purification of at least 400 times (some are during refining of Gd) Prompt energy (Me. V) 232 Th: 10 m. Bq/ton (2. 5 e-3 ppb) 232 Th (1 ms, 2 ms) 238 U (10 s, 160 s) 227 Ac Total 227 Ac Delayed energy (Me. V) 33

Calibration u Daya Bay: weekly calibration ð ACU (enable >99. 7% μ eff. ): LED, Ge, Co, 241 Am-13 C (0. 5 Hz) ð Special ACU: Cs, Mn, Am-Be ð Manual (4π): Co, 238 Pu-13 C (4% 6 Me. V gamma) u u u 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 u u u 4. 5 m in diameter ESR 2 cm thick film: 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 1 cm Acrylic sheet PMT Cover age pe yield (pe/Me. V) Daya Bay 192 8" ~6% 163 pe yield /Coverage 1. 77 RENO 354 10" ~15% 230 1 35

Reflective Panel in Detector 36

Next Step: Daya Bay-II Experiment DYB-II has been approved in China in Feb. 2013 Equivalent to CD 1 of US DOE Daya Bay II u u u 20 kton LS detector 3%/ E resolution Rich physics ð Mass hierarchy ð Precision measurement of 4 oscillation parameters to <1% ð Supernovae neutrino ð Geoneutrino ð Sterile neutrino ð Atmospheric neutrinos ð Exotic searches Talk by Y. F. Wang at ICFA seminar 2008. . . Nu. Fact 2012; by J. Cao at Nutel 2009. . . NPB 2012 (Shen. Zhen); Paper by L. Zhan, Y. F. Wang, J. Cao, L. J. Wen, PRD 78: 111103, 2008; PRD 79: 073007, 2009 37

The reactors and possible sites Daya Bay Huizhou Lufeng Yangjiang Taishan Status Operational Planned Under construction Power 17. 4 GW 18. 4 GW Kaipin, Jiangmeng, Guang Dong Huizhou Lufeng Daya Bay Hong Kong Taishan Yangjiang 38

Detector Concept Muon tracking Stainless Steel Tank Water Seal Water Buffer 10 kt Oil buffer 6 kt ~15000 20” PMTs optical coverage: 70 -80% Liquid Scintillator 20 kt Acrylic sphere：φ34. 5 m SS sphere ： φ 37. 5 m VETO PMTs 1) 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 39

DYB-II Energy Resolution u DYB-II MC, based on DYB MC (p. e. tuned to data), except ð ð DYBII Geometry and 80% photocathode coverage SBA PMT: max. QE from 25% -> 35% Lower detector temperature to 4 degree (+13% light) LS attenuation length (1 m-tube measurement@430 nm) l l from 15 m = absoption 24 m + Raylay scattering 40 m to 20 m = absorption 40 m + Raylay scattering 40 m Uniformly Distributed Events R 3 After vertex-dep. correction 40

Discovery Power Taking into account m 232 from T 2 K and Nova in the future： Contribution from absolute m 232 measurement If m 232 at 1% precision，mass hierarchy could be determined to ~5 in 6 years. (core distribution and energy non-linearity may degrade it a little bit. Current DYB II m 212 3% 0. 6% m 223 5% 0. 6% sin 2 12 6% 0. 7% sin 2 23 20% N/A sin 2 13 14% 4% ~ 15% Will be more precise than CKM matrix elements ! Probing the unitarity of UPMNS to ~1% level 41

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

DYBII: Brief schedule u u u u 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 T 2 K beam exotic S. B. Kim, talk at Neutrino 2012 44

Summary u u 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 ð Mass hierarchy ð Precision measurement of mixing parameters to < 1% unitarity test of the mixing matrix ð Sterile neutrinos, Neutrino magnetic moments, . . . u 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