First Result of NEOS Neutrino Experiment for Oscillation at Short baseline Kim Siyeon Chung-Ang University Seoul, Korea On behalf of NEOS Collaboration July 15, 2017 ICRC 2017, Busan 1
First Result of NEOS • NEOS Publication • Y. J. Ko et al., Sterile neutrino search at the NEOS experiment , Phys. Rev. Lett. 118(12), 121802 (2017) • Y. J. Ko et al., Comparison of fast neutrino rates for the NEOS experiment , J. Korean Phys. Soc. 69(11), 1651 (2016) • B. R. Kim et al., Pulse shape discrimination capability of metal-loaded organic liquid scintillators for a short-baseline reactor neutrino experiment , Phys. Scripta 90(5), 055302 (2015) • B. R. Kim et al ., Development and mass production of a mixture of LAB- and DIN- based gadolinium loaded liquid scintillator for the NEOS experiment, J. Radioanal. Nucl. Chem. 310(1), 311 (2016) • More papers on analysis and instruments are in progress. • Collaborators: 20 in 7 institutes • (1) Joo, K., Kim, B.R., (2) Ko, Y.J., Jang, C.H., Jeon, (3) E. J., Kim, Y., Lee, J., Lee, J.Y., Oh, Y., Park, H.K., Park, K.S., (4) Han B., Sun, K.M., (5) Park, H., (6) Kim, H., Lee, J., (7) Kim, H.S., Kim, J., and Seo, K.M. July 15, 2017 ICRC 2017, Busan 2
NEOS: Motivation and Purpose • Reactor Anomalies Mention et al, 2011 • Flux deficit • 5-MeV excess RENO July 15, 2017 ICRC 2017, Busan 3
NEOS: Motivation and Purpose • Reactor Anomalies • Flux deficit • 5-MeV excess NEOS baseline 24 m • Single detector needs • T o scan the possibility of the existen ce of a sterile neutrino of the mass - an accurate reference reactor a ~1 eV ntineutrino flux/spectrum - understanding the detector resp • To analyze the spectral shape onse is crucial, especially energ (not the absolute rate) of react y-charge relation or antineutrino July 15, 2017 ICRC 2017, Busan 4
Experiment Site: Habit Nuclear Power Plant in Younggwang, Korea - 2.8-GW th commercial reactor - Core size: 3.1-m diameter and 3.8-m height - Low enriched Uranium fuel (4.6% 235 U) Detector in Tendon Gallery - ~24-m baseline and ~20-m.w .e overburden ICRC 2017 ✦ 4 5 6 3 2 1 July 15, 2017 ICRC 2017, Busan 5
Livetime + IBD event rate • 46 days’ reactor off data + 180 day ’ s reactor on data + calibration - stable reactor operation, ~90% DAQ efficiency DAQ Livetime (%) Neutrino runs Test/Calibration 100 80 60 40 20 Sep '15 Nov '15 Jan '16 Mar '16 May '16 July 15, 2017 ICRC 2017, Busan 6
Livetime + IBD event rate • 46 days’ reactor off data + 180 day ’ s reactor on data + calibration - stable reactor operation, ~90% DAQ efficiency DAQ Livetime (%) Neutrino runs Test/Calibration 100 80 60 40 20 Sep '15 Nov '15 Jan '16 Mar '16 May '16 July 15, 2017 ICRC 2017, Busan 7
Active Reactor Core Fission Fraction 0.8 0.7 0.6 0.5 0.4 0.3 0.2 U-238 0.1 0 0 5000 10000 15000 Burn-up [MTU/MWD] • 177 fuel rods, low enriched (4.65%) uranium-235 (LEU) fuel • Refueling by changing 1/3 of fuel rods for each burn-up cycle (~1.5 year) • Active core size: 3.1 m ( φ ), 3.8 m (h) July 15, 2017 ICRC 2017, Busan 8
Detector Location / Baseline p.d.f. Mean Mean S 23.64 23.64 0.4 Active Core td Dev Std Dev 0.8146 0.8146 0.3 (20 m.w.e) 0 overburden 0.2 0.1 ~8 m 22 23 24 25 26 L [m] Neutrino travel distance distribution: - Beta decays uniformly generated in cyli ndrical core NEOS Detector - IBD interaction points uniformly distribut ed in target Distance-weighted effect: 1/L 2 - T endon Gallery Entrance / Exit July 15, 2017 ICRC 2017, Busan 9
Construction July 15, 2017 ICRC 2017, Busan 10
Detector Specification Linear Alkyl Benzene • Homogeneous LS target — 1008 L volume (R 51.5, H 121) cm — LAB+UG-F (9:1) — 0.5% Gd loaded for high neutr on capture efficiency — 38 8 ″ PMT in mineral oil buffer • Shieldings — 10 cm B-PE (n), 10 cm Pb ( γ ) — active muon counter 5T PTFE reflectors • Data AcQuisition — 500 MS/s FADC (waveform) — 62.5 MS/s SADC ( μ veto) • Source calibration through chi mney July 15, 2017 ICRC 2017, Busan 11
IBD Reconstruction Counts /sec/10keV Selection rules developed for best S/N ratio: Target Single Events 1 All: Reactor OFF • Prompt energy: 1-10 MeV All: Reactor ON 10 − 1 • Delayed energy: 4-10 MeV Muon veto cut:Reactor OFF Muon veto cut:Reactor ON • Time coincidence: 1-30 μ s 10 − 2 • Multiplicity: no event before (after) 30 (150) S1+S2+background 10 − 3 μs from the prompt/delayed pair • Muon veto: 150 μ s 10 − 4 • Pulse shape discrimination 1 2 3 4 5 6 7 8 9 Recontructed Energy [MeV] Counts /day/0.1MeV Counts /day/0.8µs 60 Reactor ON Reactor ON 100 Reactor OFF S2 Reactor OFF 40 50 20 0 0 4 5 6 7 8 9 0 10 20 30 40 50 60 Delayed Energy [MeV] Neutron Capture Time [µs] July 15, 2017 ICRC 2017, Busan 12
Pulse Shape Discrimination Reactor OFF 10 2 Reactor ON Events /day Fast n 10 e, γ 1 10 − 1 − 10 − 5 0 5 10 15 20 p ( t ) psd • IBD events vs. fast neutron ’ s scattering events • Qtail/Qtot or meantime of waveform. • LAB + DIN (UG-F) mixed LS. • More than 70 % of IBD background could be reduced after PSD. July 15, 2017 ICRC 2017, Busan 13
Prompt Energy Spectrum S neos / MC( Φ hm ⋅ 60 σ ) Vogel Data signal ( S neos =ON-OFF) 1.1 Data/Prediction Systematic total Data background (OFF) 50 Events /day/100 keV MC no oscillation ( Φ hm ⋅ σ ) 1.0 Vogel MC no oscillation ( S dyb ) 40 0.9 1 2 3 4 5 6 7 10 30 Prompt Energy [MeV] S / MC( S ) 1.1 neos dyb Systematic total Data/Prediction 20 1.0 10 0.9 0 7 ⋅ ⋅ 10 1 2 3 4 5 6 7 10 1 2 3 4 5 6 Prompt Energy [MeV] Prompt Energy [MeV] • Signal / Noise ~ 22 • vs H-M: 5 MeV bump, not so practical to do the oscillation analysis • vs Daya Bay: bump not totally disappeared, fission fraction difference • Systematic uncertainties for the shape analysis: reference spectrum > energy recon. >> background fluc., S2 cut efficiency … July 15, 2017 ICRC 2017, Busan 14
Active-to-Sterile Oscillation • c 2 minima are found at (sin 2 2 θ , Δ m 2 )=(0.04, 1.3 eV 2 ), (0.05, 1.73 eV 2 ) with Δ c 2 = c 2 3 n − c 2 4 n = 6.5. • p-value ~ 22%. • No strong sign of active-to-sterile n oscillation. Entries (a.u.) 10000 1.1 NEOS/Daya Bay MC pseudo-experiment (c) 8000 no sterile neutrino. Systematic total Data/Prediction χ 2 dist. (NDF=2) 6000 1.0 4000 (1.73 eV 2 , 0.050) (2.32 eV 2 , 0.142) 2000 0.9 ⋅ ⋅ 1 2 5 6 7 10 3 4 00 Prompt Energy [MeV] 2 4 6 8 10 12 14 χ 2 - χ 2 3 ν 4 ν July 15, 2017 ICRC 2017, Busan 15
Active-to-Sterile Oscillation • Exclusion limits • Raster scan with c 2 distribution • Exclude Δ m 2 < 3 eV 2 , • Rule out models, including RAA (reactor antine utrino anomaly) and recent global analyses. July 15, 2017 ICRC 2017, Busan 16
Thank you. NEOS Collaboration July 15, 2017 ICRC 2017, Busan 17
Backup July 15, 2017 ICRC 2017, Busan 18
Non-Linear Charge Response to Energy @ Neutrino 2016 NEOS Preliminary Charge/Energy [pC/MeV] PoBe(Ch) 208 550 Tl(O) 60 Co( Φ ) n-H( Φ ) 500 40 K(P) Source position PoBe(Ch) ( Φ ) target center (P) PMT 450 137 Cs( Φ ) (O) outside (Ch) calibraion chimney 1 2 3 4 5 6 7 8 True Gamma Energy [MeV] • Signal quenched at low energy • Cerenkov light important at higher energy July 15, 2017 ICRC 2017, Busan 19
NEOS status • NEOS is over due to regular maintenance of the tendon gallery (once every 5 years) • No strong evidence of oscillation from active-to-(~1 eV) sterile mixing. • T endon gallery is a nice place for reactor neutrino experiment, but • Severe escaping γ effect with a small volume detecter without γ catcher. • Measurement of 1 whole burn-up cycle should help to understand the spectrum in detail. • Rate analysis, Absolute spectrum, NEOS 235 U P1 P2 239 Pu 238 U 241 Pu July 15, 2017 ICRC 2017, Busan 20 21
Dedicated room for neutrino experiments active core NEOS Proposed new room @ tendon experimental gallery room (proposed) core diameter 312.4 cm 365 cm core height 381 cm thermal power 2815 MW 3983 MW distance to core 24 m ~18 m * overburden >20 muon rate ~0.2 cm -2 min -1 * rectangular space 4 x 2.5 x 8 x 5 x 4 * (WxDxH m 3 ) 3.3 # of IBD events ~2000 ~5000 to be detected ( per day per day * ground NEOS detector) level July 15, 2017 ICRC 2017, Busan 21
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