Observation of Reactor Antineutrino Disappearance at RENO

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Observation of Reactor Antineutrino Disappearance at RENO. Soo -Bong Kim for the RENO Collaboration KNRC, Seoul National University (presented at CERN on May 7, 2012). YongGwang ( 靈光 ) : . Outline. Introduction Experimental setup & detector Data-taking & data set Calibration
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Observation of Reactor Antineutrino Disappearance at RENOSoo-Bong Kim for the RENO CollaborationKNRC, Seoul National University(presented at CERN on May 7, 2012)YongGwang (靈光) : Outline
  • Introduction
  • Experimental setup & detector
  • Data-taking & data set
  • Calibration
  • Event selection
  • Efficiency & Background
  • Reactor antineutrino prediction
  • Systematic uncertainties
  • Results
  • Summary
  • Neutrino OscillationPMNS Neutrino Mixing Anglesand CP Violation12n1n2Reactor Antineutrino Oscillation2313(?)n313from Reactor and Accelerator Experiments* Reactor- Clean measurement of 13 with no matter effects* Accelerator - mass hierarchy + CP violation + matter effects
  • Complementarity :
  • Combining results from accelerator and reactor based experiments could offer the first glimpse of CP.
  • Efforts for Finding q13
  • Chooz (2003) & Palo Verde (2000): No signal
  • sin2(2q13) < 0.12 at 90% C.L.
  • Daya Bay (Mar. 8. 2012)
  • 5.2 s observation
  • T2K : 2.5 s excess (2011)
  • sin2(2q13) = 0.092 ± 0.016(stat.)±0.005(syst.)0.03 < sin2(2q13) < 0.28 at 90% C.L. for N.H. 0.04 < sin2(2q13) < 0.34 at 90% C.L. for I.H.
  • MINOS : 1.7 s excess (2011)
  • 0 < sin2(2q13) < 0.12 at 90% C.L. for N.H. 0.04 < sin2(2q13) < 0.19 at 90% C.L. for I.H.
  • RENO (Apr. 2. 2012)
  • 4.9 s observation
  • sin2(2q13) = 0.113 ± 0.013(stat.)±0.019(syst.)
  • Double Chooz : 1.7 s measurement (2011)
  • sin2(2q13) = 0.086 ± 0.041(stat.) ± 0.030(syst.)To be published in PRL
  • Submitted on Apr. 2, and resubmitted on Apr. 6 after revision
  • Accepted on Apr. 23 for publication
  • Expected to appear on May 11 (Daya Bay PRL : April 27)
  • To be included in a new edition of Particle Data this yearRENO Collaboration(12 institutions and 40 physicists)
  • ChonbukNational University
  • ChonnamNational University
  • Chung-Ang University
  • Dongshin University
  • Gyeongsang National University
  • Kyungpook National University
  • Pusan National University
  • Sejong University
  • SeokyeongUniversity
  • Seoul National University
  • SeoyeongUniversity
  • SungkyunkwanUniversity
  • Total cost : $10M
  • Start of project : 2006
  • The first experiment running with both near & far detectors from Aug. 2011
  • RENOChoozRENO Expected Sensivity
  • CHOOZ : Rosc = 1.01 ± 2.8% (stat) ± 2.7% (syst)
  • sin2(2q13) < 0.17 (90% C.L.)
  • RENO : statistical error : 2.8% → 0.3%
  • systematic error : 2.7% → <0.5%
  • sin2(2q13) > 0.02 (for 90% C.L.)
  • sin2(2q13) > 0.035 (for 3s discovery potential)
  • 10 times better sensitivity
  • Larger statistics
  • - More powerful reactors (multi-core) - Larger detection volume - Longer exposureG. Fogliet al. (2009)
  • Smaller experimental errors
  • - Identical multi detectors
  • Lower background
  • - Improved detector design - Increased overburdenRENO Experimental SetupNear Detector290m1380mFar DetectorContribution of Reactor to Neutrino Flux at Near & Far Detectors
  • Accurate measurement of baseline distances to a precision of 10 cm using GPS and total station
  • Accurate determination of reduction in the reactor neutrino fluxes after a baseline distance, much better than 0.1%
  • RENO Detector
  • 354 ID +67 OD 10” PMTs
  • Target : 16.5 ton Gd-LS, R=1.4m, H=3.2m
  • Gamma Catcher : 30 ton LS, R=2.0m, H=4.4m
  • Buffer : 65 ton mineral oil, R=2.7m, H=5.8m
  • Veto : 350 ton water, R=4.2m, H=8.8m
  • Summary of Detector Construction
  • 2006. 03 : Start of the RENO project
  • 2008. 06 ~ 2009. 03 : Civil construction including tunnel excavation
  • 2008. 12 ~ 2009. 11 : Detector structure & buffer steel tanks
  • completed
  • 2010. 06 : Acrylic containers installed
  • 2010. 06 ~ 2010. 12 : PMT test & installation
  • 2011. 01 : Detector closing/ Electronics hut & control room built
  • 2011. 02 : Installation of DAQ electronics and HV & cabling
  • 2011. 03 ~ 06 : Dry run & DAQ debugging
  • 2011. 05 ~ 07 : Liquid scintillator production & filling
  • 2011. 07 : Detector operation & commissioning
  • 2011. 08 : Start data-taking
  • PMT Mounting (2010. 8~10)PMT Mounting (2010. 8~10)Detector Closing (2011. 1)Near : Jan. 21, 2011Far : Jan. 24, 2011Detection of Reactor Antineutrinos(prompt signal)(delayed signal)~180 ms+ p  D + g (2.2 MeV) ~28 ms(0.1% Gd)+ Gd  Gd + g‘s (8 MeV)
  • Neutrino energy measurement
  • CnH2n+1-C6H5 (n=10~14)Gd Loaded Liquid Scintillator
  • Recipe of Liquid Scintillator
  • * Stable light yield over the time period : ~250 pe/MeV* Measured cosmic induced neutron’sGd capture timeLiquid(Gd-LS/LS/MO/Water) Production & Filling(May-July 2011)Gd-LS filling for Target Gd Loaded Liquid ScintillatorWater filling for Veto LS filling for Gamma CatcherGd Loaded Liquid Scintillator 1D/3D Calibration System
  • Calibration system to deploy radioactive sources in 1D & 3D directions
  • Radioactive sources : 137Cs, 68Ge, 60Co, 252Cf
  • Laser injectors
  • Data Acquisition System
  • 24 channel PMT input to ADC/TDC
  • 0.1pC, 0.52nsec resolution
  • ~2500pC/ch large dynamic range
  • No dead time (w/o hardware trigger)
  • Fast data transfer via Ethernet R/W
  • Data-Taking & Data Set
  • Data-taking efficiency
  • Data taking began on Aug. 1, 2011 with both near and far detectors.
  • Data-taking efficiency > 90%.
  • Trigger rate at the threshold energy of 0.5~0.6 MeV : 80 Hz
  • Data-taking period : 228 days Aug. 11, 2011 ~ Mar. 25, 2012
  • Event rate before reduction
  • 208Tl
  • A candidate for a neutron capture by Gd
  • 40Kn capture by Gd2 MeV6 MeV10 MeVRENO’s Status & Plan
  • RENO was the first reactor neutrino experiments to search for q13 with both near & far detectors running, from the early August 2011.
  • RENO started to see a signal of reactor neutrino disappearance from the late 2011.
  • According to reported schedules of the other experiments, RENO was thought to present a result first soon. We planned to publish our first results in April without a hurry and to present them in the Neutrino 2012.
  • But …..
  • PMT Threshold & Gain Matching
  • PMT gain :set 1.0x107 using a Cs source at center
  • Gain variation among PMTs : 3% for both detectors.
  • discri. thr.-0.4mV-0.5mV-0.6mV-0.7mV-1.0mVGain (10 7)
  • PMT threshold : determined by a single photoelectron response using a Cs source at the center
  • Charge(counts)Energy Calibration
  • Near Detector
  • Far Detector
  • Cs 137Ge 68(662 keV)(1,022 keV)Cf 252Co 60(2.2/7.8 MeV)(2,506 keV)Energy Scale CalibrationNear DetectorFar DetectorCfCfCoCoCfCfGeGeCsCs
  • ~ 250 pe/MeV(sources at center)
  • Identical energy response (< 0.1%) of ND & FD
  • Slight non-linearity observed
  • Detector Stability & Identity
  • Cosmic muon induced neutron’s capture by H
  • Near Detector
  • Far Detector
  • Capture Time
  • IBD candidate’s delayed signals (capture on Gd)
  • Delayed Energy
  • Near Detector
  • Far Detector
  • IBD Event Signature and Backgrounds
  • IBD Event Signature
  • Prompt signal (e+) : 1 MeV 2g’s + e+ kinetic energy (E = 1~10 MeV)
  • Delayed signal (n) : 8 MeVg’s from neutron’s capture by Gd
  • ~28 ms (0.1% Gd) in LS
  • Delayed Energy Prompt Energy
  • Backgrounds
  • Random coincidence between prompt and delayed signals (uncorrelated)
  • 9Li/8He b-n followers produced by cosmic muonspallation
  • Fast neutrons produced by muons, from surrounding rocks and inside detector (n scattering : prompt, n capture : delayed)
  • IBD Event Selection
  • Reject flashers and external gamma rays : Qmax/Qtot < 0.03
  • Muon veto cuts : reject events after the following muons
  • (1) 1 ms after an ID muon with E > 70 MeV, or with 20 < E < 70 MeV and OD NHIT > 50
  • (2) 10 ms after an ID muon with E > 1.5 GeV
  • Coincidence between prompt and delayed signals in 100 ms
  • - Eprompt : 0.7 ~ 12.0 MeV, Edelayed : 6.0 ~ 12.0 MeV
  • - coincidence : 2 ms < Dte+n < 100 ms
  • Multiplicity cut : reject pairs if there is a trigger in the preceding 100 ms window
  • Random Coincidence Backgrounds
  • Calculation of accidental coincidence
  • DT = 100 ms time window
  • Near detector :
  • Rprompt = 8.8 Hz, Ndelay= 4884/day →
  • Far detector :
  • Rprompt = 10.6 Hz, Ndelay= 643/day →
  • 9Li/8He b-n Backgrounds
  • Find prompt-delay pairs after muons, and obtain their time interval distribution with respect to the preceding muon.
  • 9Li energy spectrum
  • 9Li time interval distribution
  • Time interval (ms)Energy (MeV)
  • Near detector :
  • Far detector :
  • 9Li/8He b-n Backgrounds
  • 9Li production at far detector
  • 9Li production at near detector
  • Fast Neutron Backgrounds
  • Obtain a flat spectrum of fast neutron’s scattering with proton, above that of the prompt signal.
  • Near detectorFar detector
  • Near detector :
  • Far detector :
  • Spectra & Capture Time of Delayed SignalsNear DetectorFar DetectorNear Detector t = 27.8 ± 0.2msec
  • Observed spectra of IBD delayed signals
  • Far Detector t = 27.6 ± 0.4msecSummary of Final Data SampleMeasured Spectra of IBD Prompt SignalNear Detector154088 (BG: 2.7%)Far Detector17102 (BG: 5.5%) Expected Reactor Antineutrino Fluxes
  • Reactor neutrino flux
  • - Pth : Reactor thermal power provided by the YG nuclear power plant - fi : Fission fraction of each isotope determined by reactor core simulation of Westinghouse ANC - fi(En) : Neutrino spectrum of each fission isotope [* P. Huber, Phys. Rev. C84, 024617 (2011) T. Mueller et al., Phys. Rev. C83, 054615 (2011)] - Ei: Energy released per fission [* V. Kopeikinet al., Phys. Atom. Nucl. 67, 1982 (2004)]Observed Daily Averaged IBD RateReduction of Systematic Uncertainties
  • Detector related :
  • - “Identical” near and far detectors - Careful calibration
  • Reactor related :
  • - Relative measurements with near and far detectorsNumber of protonsDetection efficiencyNeutrino eventsYield of sin2(2q13) 1/r2
  • Maury Goodman’s neutrino newsletter (5/5/2012):
  • F. Darwin said “In Science the credit goes to the man who convinces the world, not to the man to whom the idea first occurred.”
  • But he wishes to give credit to Russians who first proposed a two detector neutrino reactor disappearance experiment : L. Mikaelyan & V. Sinev.
  • Efficiency & Systematic UncertaintiesReactor Antineutrino Disappearance
  • A clear deficit in rate (8.0% reduction)
  • Consistent with neutrino oscillation in the spectral distortion
  • c2 Fit with PullsDefinitive Measurement of q13
  • 4.9s significant signal
  • Near detector: 1.2% reduction
  • Far detector: 8.0% reduction
  • c2 Distributions for Uncertainties Future Plan for Precision Measurement of q13
  • RENO
  • (4.9 s)
  • Daya Bay
  • (5.2 s)
  • Contributions of the systematic errors :
  • - Background uncertainties : 0.0165
  • (far : 5.5%×17.7% = 0.97%, near : 2.7%×27.3% = 0.74%)
  • - Reactor uncertainty (0.9%) : 0.0100
  • - Detection efficiency uncertainty (0.2%) : 0.0103
  • - Absolute normalization uncertainty (2.5%) : 0.0104
  • Remove the backgrounds !
  • Spectral shape analysis
  • Summary
  • RENO was the first experiment to take data with both near and far detectors, from August 1, 2011.
  • RENO observed a clear disappearance of reactor antineutrinos.
  • RENO measured the last, smallest mixing angle q13 unambiguously that was the most elusive puzzle of neutrino oscillations
  • Surprisingly large !!!
  • → A plenty of tasks ahead for neutrino physicists
  • Prospective Future
  • A surprisingly large value of q13 :
  • (Save a lot of dollars for the future neutrino experiments which may need reconsideration of their designs!!)
  • → (1) Provides a complete picture of neutrino oscillations
  • (2) Open a bright window of understanding why there is much more matter than antimatter in the Universe today
  • A prospective future for neutrino physics due to a large value of q13 !!!
  • Our measurement will strongly promote the next round of neutrino experiments to find the CP phase.
  • Complimentary measurements between accelerator experiments and reactor experiments will provide significant information on the CP phase.
  • RENO-50RENO-50L~50km experiment may be anatural extension of current Reactor-q13 Experiments* q13 detectors can be used as near detector* Small background from other reactors.RENO-50WaterLAB (5 kton)3000 10” PMTs25 m20 m20 m25 mRENO-50 5000 tons ultra-low-radioactivity Liquid Scintillation Detector500 10” OD PMTsRENO8.8 m5.8 m5.4 m8.4 m Precise measurement of q12in a year ← current accuracy : 5.4%Physics with RENO-50
  • Determinationof mass hierarchy Dm213
  • Neutrino burst from a Supernova in our Galaxy :
  • ~1500 events (@8 kpc)
  • Geo-neutrinos : ~ 300 geo-neutrinos for 5 years
  • Solar neutrinos : with ultra low radioacitivity
  • Reactor physics : non-proliferation
  • Detection of T2K beam : ~120 events/year
  • Test of non-standard physics : sterile/mass varying neutrinos
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