NuFact 2012, Williamsburg, VA RENO Yeongduk Kim, Sejong University On behalf of RENO collaboration NuFact 2012, Williamsburg, VA 2012. 7. 23-28
Contents Q13 measurement with reactor neutrinos Overview of RENO Data Taking and Data Reduction Calibration Data of RENO Background Reduction Chi2 Analysis & results of Q13 Summary & Perspectives
Q13 Measurements with Reactor and Accelerator - Clean measurement of 13 with no matter effects * Accelerator - mass hierarchy + CP violation + matter effects Two experiments are complementary..
Reactor Neutrino Experiment at a Glance ν e + n Gd γ ~30μs Delayed signal E å ~ 8 MeV g prompt signal Inverse Beta Decay q13 Dominant sin2(213)=0.04 sin2(213)=0.1 sin2(213)=0.2 E (MeV) “near” “far” q12 Dominant
RENO Collaboration (12 institutions and 40 physicists) Project of Only Korean Institutes (12 institutions and 40 physicists) Chonbuk National University Chonnam National University Chung-Ang University Dongshin University Gyeongsang National University Kyungpook National University Pusan National University Sejong University Seokyeong University Seoul National University Seoyeong University Sungkyunkwan University Total cost : $10M Start of project : 2006 The experiment running with both near & far detectors from Aug. 2011
Global fits Fogli et al., arXiv:1205.5254
RENO Sites Seoul RENO Y2L Far Detector Near Detector 1380m 290m
Contributions of Reactors to Neutrino Flux Far ( % ) Near (% ) 1 13.73 6.78 2 15.74 14.93 3 18.09 34.19 4 18.56 27.01 5 17.80 11.50 6 16.08 5.58 Accurate measurement of baseline distances to a precision of 10 cm using GPS and total station. Accurate determination of reactor neutrino fluxes require small, uncorrelated reactor power uncertainties.
RENO Detector 354 10” ID PMTs : 14% surface coverage 67 10” OD PMTs Both PMTs : HAMAMATSU, R7081 Mu-metal shielding for each PMT. (-5cm) No special reflector for ID Tyvek reflector at OD LAYER D (cm) H vessel Filled with Mass (tons) Target 280 320 Acrylic Gd(0.1%) +LS 16.5 Gamma catcher 400 440 LS 30.0 Buffer 540 580 SUS Mineral oil 64.4 Veto 840 880 Concrete water 352.6
Summary of Milestones for RENO 2006. 03 : Start of the RENO project 2008. 06 ~ 2009. 03 : Civil construction including tunnel excavation 2008. 12 ~ 2009. 11 : Detector structure & buffer tanks complete. 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. 05 ~ 07 : Liquid scintillator production & filling 2011. 08 : Start data-taking.
Completed RENO Detector (Feb. 2011) Liquid Scintillator Production System DAQ Electronics Calibration System Control Room
Gd Loaded Liquid Scintillator Recipe of Liquid Scintillator CnH2n+1-C6H5 (n=10~14) Aromatic Solvent & Flour WLS Gd-compound LAB PPO + Bis-MSB 0.1% Gd+(TMHA)3 (trimethylhexanoic acid) Gd concentrations in Gd-LS sample measured . ~0.11%, stability ~ year. FAR NEAR
10” PMT R7081 [rms/mean] Optimized Mu shielding. Mu metal shielding up to 5 cm to Top. All 842 PMTs are working w/o failure for last 1 year. Relative Light output [rms/mean]
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 : 229 days Aug. 11, 2011 ~ Mar. 26, 2012 2 MeV 6 MeV 40K 10 MeV 208Tl n capture by Gd Event rate before reduction A candidate for a neutron capture by Gd
Spectra w/ sources after NPE adjustment Near Detector Far Detector Cs 137 (662 keV) Ge 68 (1,022 keV) Co 60 (2,506 keV) Cf 252 (2.2/7.8 MeV)
Energy Calibration w/ source Near Detector Far Detector Cf Cf Co Co Cf Cf Ge Ge Cs Cs ~ 250 pe/MeV (sources at center) Identical energy response (< 0.1%) of ND & FD Slight non-linearity observed. “Prompt” energy is calibrated with gamma sources. Slight difference between (e+ kinetic energy) and (Prompt energy-1.02 MeV) is expected.
Long-term Stabilities Near Detector Far Detector Capture Time Cosmic muon induced neutron’s capture by H Near Detector Far Detector n capture signals (capture on Gd)
Cuts for n Events Reject flashers and external gamma rays : Qmax/Qtot < 0.03 Muon veto cuts : reject events after the following muons 1 ms DEAD time for E(ID) > 70 MeV 20MeV < E(ID) < 70 MeV & NPMT (OD) > 50 10 ms DEAD time for E(ID) > 1.5 GeV Coincidence : 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 an any trigger in the preceding 100 ms window.
Spectra & capture time of neutrons Near Detector Far Detector Observed spectra of Gd+n capture signal 155Gd (18.5%) 157Gd (81.5%) t = 27.8 ± 0.2 msec Near Detector t = 27.6 ± 0.4 msec Far Detector
Backgrounds II – 9Li/8Be Find prompt-delay pairs after muons, and obtain their time interval distribution with respect to the preceding muon. Time interval (ms) 9Li time interval distribution Energy (MeV) 9Li energy spectrum Near detector : Far detector :
We have tried to extend to lower energy muons, but limited by high rates. NEAR FAR We have extrapolated higher energy data to lower threshold data. NEAR FAR
Backgrounds III – fast neutrons Obtain a flat spectrum of fast neutron’s scattering with proton, above that of the prompt signal. Near detector Far detector Near detector : Far detector :
Summary of Final Counts
Prompt energy spectra of neutrinos Near Detector 154088 (BG: 2.7%) Far Detector 17102 (BG: 5.5%) Prompt energy spectra shows enhanced rates in 4-6 MeV considering expected neutrino spectra. Detector response functions are not studied in detail yet. More calibration work is underway.
n Flux estimation Supplied by power plant Daily thermal power Last Fuel Exchange period Fission fractions
Estimation of n event rates
Observed Daily Averaged n Rate
Efficiency & Systematic Uncertainties
Reactor Antineutrino Disappearance Clear deficit in rates , consistent with neutrino oscillation with the energy spectra. E>6 MeV distortion is not understood yet.
Results of q13 4.9s significant signal Near detector: 1.2% reduction Far detector: 8.0% reduction
Effect of uncertainty of For absolute uncertainty of theta13, we have to consider the uncertainty of Fogli et al., arXiv:1205.5254
Global Picture Exclusion of non-zero 13 A consistent picture (2010) 2011.6 2012.6 2011.7 2012.6 2011.11 2012.6 2012.3 2012.6 (7.7) 2012.4 by S. Jetter Shown by Jun Cao @ ICHEP2012
Future Efforts for q13 at RENO 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 Reduce the amound of backgrounds ! Do spectral shape analysis ! More precise calibrations needed. MC (vertex reconstructions) tuning. Reactor cycle dependent flux should be included.
Summary RENO observed a clear disappearance of reactor antineutrinos. RENO measured mixing angle q13 unambiguously that was the most elusive puzzle of neutrino oscillations. Need more detail studies needed to fit L/E analysis.
Perspectives A large value of q13 : Three reactor measurement will strongly promote the next round of neutrino experiments to find the CP phase. Opens a possibility that mass hierarchy w/o matter effect or CP phase be measured in reactor experiment. Mass Hierarchy with reactor neutrinos @ 50 km
Short baseline Reactor Experiment 30MW research Reactor, Small Core size ~ 20x40x60cm Baseline 6m 50L prototype detector – background study. 500L Main Detector Location
Thank you !
Electronics & Trigger Software trigger QBEE : each channel digitized if over threshold. All the hits are sorted in time and grouped into an event if number of hits exceeds preset trigger condition. (ID:90, OD:10) Pedestal hits are collected realtime Intrinsic charge Injector into each channel for electronics calibration. Types of Trigger : ID OD LASER PEDESTAL Charge Injector Data block(20ms) Software trigger 200ns “Software” event Merge the data From front-end PCs Number of hits exceeds the threshold, Send downstream
Trigger Rates NEAR FAR Depth (mwe) 120 450 Distance from Reactor baseline(m) 294 1383 Flux weighted distance (m) 408.56 1443.99 Muon Rate (Simulation)( /m2 sec)# 5.5 0.85 Average Muon energy (GeV)# 34.3 65.2 Inner Detector (Hz) (NPMT >90)* ~280 ~110 Outer Detector (Hz) (NPMT >10)* ~533 ~66 * NPMT is counted within 50nsec. # Simulated for Near (70m), Far(200m) depths.
Backgrounds I - Accidentals 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 →
c2 Pull Analysis for Rate Only data