NEOS: Reactor neutrino experiment at short baseline 11 Sep @ TAUP 2019, Toyama Yoomin Oh
Outline •Reactor neutrino •Anomalies •Short baseline (SBL) oscillation •Introduction/status of the NEOS experiment 2019.09.09 Yoomin Oh / NEOS � 2 TAUP 2019, Toyama
Reactor neutrinos and inverse beta decay In the detector 1.0 4 Huber, Mueller x Vogel ] 2 cm prompt ] -1 -42 0.8 φ × σ MeV 3 IBD cross section [10 e + -1 0.6 Flux [fission ν̅ e 2 0.4 delayed p 1 n 0.2 n -capture by 0.0 0 2 3 4 5 6 7 8 (H, Gd, 6 Li, …) Neutrino Energy [MeV] •Average of 6-7 β -decays and anti-v’s from a fission of an element. •2 x 10 20 v / 4 π / GW th - O(10k) inverse beta decay events occur in 1000 kg of organic scintillator with 10% mass of hydrogen atom at 10 m distance from a gigawatts-thermal-power reactor. Yoomin Oh / NEOS � 3 TAUP 2019, Toyama
Anomalies and a new state? Gallex/SAGE LSND (2009) (2001) MiniBooNE (2013) mixing with a ~1eV state?! white paper (2012) Mention (2011) Gariazzo (2016) Yoomin Oh / NEOS � 4 TAUP 2019, Toyama
Miscalculated flux? RENO (2019) DChooz (v-fact ’19) •Disagreement in rate and shape, at hundreds of meters distances from LEU reactors. •Not likely an energy scale problem. •Should be checked with new SBL data. Yoomin Oh / NEOS � 5 TAUP 2019, Toyama
��� Reactor SBL oscillation � � �� �� 2 · � 1 . 27Δ m 2 L ν e ) ∼ 1 − ��� 2 2 θ 14 ��� 2 P (¯ ν e → ¯ E ν Δ m 2 (1) Data / MC (3v) sin 2 2 θ *illustration 1.8 Antineutrino energy (MeV) 10 ~1.0 Reconstructed prompt energy (MeV) 10 •Oscillation pattern smeared out by: distance / energy resolution, uncertainties in reference spectrum, statistics, background, … Yoomin Oh / NEOS � 6 TAUP 2019, Toyama
NEOS •Neutrino Experiment for Oscillation at Short baseline, •Test of RAA and search for active-to-sterile neutrino oscillation with Δ m 2 ~ 1 eV 2 , •Project launched in 2011, •Using a commercial reactor core and 1000 L of homogeneous Gd- loaded liquid scintillation detector, •Phase-I data taking: Aug 2015 ~ May 2016, Phase-II data taking: Sep 2018 ~ Now (~ Summer 2020), •20 collaboration members from 7 institutes. Yoomin Oh / NEOS � 7 TAUP 2019, Toyama
Reactor site 5 6 4 3 2 1 • Hanbit NPP in Yeonggwang ( 靈光 , ghost light), Korea, • Distance between neighboring cores: 256 m (less than 1% contribution from each of them), • Same reactor complex used for RENO experiment Yoomin Oh / NEOS � 8 TAUP 2019, Toyama
Hanbit-5 reactor Fission Fraction 0.8 0.7 0.6 U-235 0.5 0.4 Pu-239 0.3 0.2 U-238 0.1 Pu-241 0 0 5000 10000 15000 Burn-up [MTU/MWD] •OPR-1000 reactor, 2815 MW th , •177 fuel rods, low enriched (~4%) uranium-235 (LEU) fuel, •Refueling by changing 1/3 of fuel rods for each burn-up cycle (~1.5 years), •Active core size: 3.1 m ( φ ) x 3.8 m (h). Yoomin Oh / NEOS � 9 TAUP 2019, Toyama
Tendon gallery < L > = 2 8 m 3 . 7 m 3.3 +0.6 m 3 m • Not a radioactivity controlled area: no background related to reactor operation, • Muon rate: about 1/5 of surface (~0.17 μ /cm 2 /min), • Maintenance work every 5 years. Yoomin Oh / NEOS � 10 TAUP 2019, Toyama
Environmental condition Yoomin Oh / NEOS � 11 TAUP 2019, Toyama
NEOS detector Muon counter: 10 cm thick B-PE, 3(5)-cm thick plastic scintillator 10 cm thick Pb panels surround the most outside for passive shieldings. except for bottom. Homogeneous 1000 L Data acquisition with ( Φ 103 x L121 cm) volume, - 500 mega-sampling/sec FADC for target PMTs, 0.5% Gd-doped LS, 90% LAB+ 10% UG-F, - 62.5 mega-sampling/sec ADC for muon counter PMTs. seen by 2 x 19 8-inch PMTs, Slow monitoring: temperatures, radon level, PMT HVs. PTFE reflector on inner walls. Yoomin Oh / NEOS � 12 TAUP 2019, Toyama
Phase-I result PRL 118 (2017) 121802 •LEU reactor, 24 m distance. •The 5 MeV bump is there. •Found no strong evidence of active-to-sterile oscillation, compared to Daya Bay spectrum. Yoomin Oh / NEOS � 13 TAUP 2019, Toyama
NEOS phase-II •Shape + rate analysis for sterile neutrino search, and/or, •Precision measurement of the spectrum itself. •Spectrum evolution with the fission fraction change. •Measuring a full operation cycle (~500 calendar days) + two background periods before/after the cycle (~100 days). - Phase-I: 46 days OFF + 180 days ON as DAQ livetime. •Same detector, same reactor and same baseline as in phase-I. - Newly produced Gd-LS, - Minor modifications: leak-proof maintenance, muon counter plastic scintillator. •Data taking started in September 2018. Yoomin Oh / NEOS � 14 TAUP 2019, Toyama
NEOS phase-II Huber-235 Huber-239 Decomposed 235 1 ± σ 40 Decomposed 239 ± 1 σ Entries /day/MeV Example 235 •Not a dramatic improvement of eV Example 239 sterile neutrino search sensitivity, 20 •Decomposition of U/Pu spectra, benefitted by large fission fraction changes in a single LEU reactor. 0 2 4 6 8 Prompt Energy [MeV] Yoomin Oh / NEOS � 15 TAUP 2019, Toyama
NEOS phase-II — NEOS-I •On about half of planned — NEOS-II (Work in progress) data taking: -the second half of the fuel cycle and another maintenance period (~100 days) to measure. -measurement will be completed in Summer 2020. •Monte Carlo simulation is being revised: -light-energy non-linearity, -n-Gd capture, etc. Yoomin Oh / NEOS � 16 TAUP 2019, Toyama
Summary •NEOS measures the inverse beta decay of the reactor electron antineutrinos. •Using a 2.8 GW commercial nuclear power reactor at 24 m distance. •Homogeneous, 1000 L of Gd-loaded liquid scintillator target •Precision measurement of the reactor v spectrum. •Spectrum evolution to find the origin of the reactor anomaly. •Testing of active-to-sterile neutrino oscillation for Δ m 2 ~1 eV 2 . •We are in the middle of phase-II measurement. Yoomin Oh / NEOS � 17 TAUP 2019, Toyama
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