RENO Reactor Neutrino Experiment

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1 RENO Reactor Neutrino Experiment "Reactor neutrino oscillation" and "Development of liquid scintillators for the neutrino experiments RENO = Reactor Experiment for Neutrino Oscillation (On behalf of RENO Collaboration) K.K. Joo Chonnam National University March 17, 2015 Yonsei Particle Theory Yonsei University

2 Outline 1 st part (physics) RENO & RENO-50 Recent result of θ 13 from RENO Future project RENO-50 2 nd part (R&D) Liquid scintillators Technology for metal-loaded liquid scintillators Water-based liquid scintillator (WbLS)

3 Quick Overview Results with ~800 days of data sample New measured value of θ 13 from rate-only analysis (Neutrino 2014) Shape analysis in progress: finalizing the result now! Results of reactor neutrinos with neutron capture on H (Significant improvement since Neutrino 2014)

23, θ 13 ) Trying to measure precisely Daya Bay Double Chooz Reactor

4 Neutrino Oscillation Neutrino: elementary particle Three types of neutrinos exist & mixing among them Oscillation parameters (θ 12, θ 23, θ 13 ) Trying to measure precisely Daya Bay Double Chooz Reactor Antineutrino Oscillation RENO P( ν e ν ) e 2 1. m 1 sin 2 2θ sin Eν 2 13 L

Neutrino Mixing Parameters Matrix Components: 3 Angles (θ 12 ; θ 13 ; θ 23 ) 1 CP phase (δ) 2 Mass differences ν ν ν e μ τ U = U U e1 μ1 τ1 U U U e2 μ2 τ2 U U U e3 μ3 τ3 ν ν ν 1 2 3 U 1 = 0 0 iδ 0 0

5 Neutrino Mixing Parameters Matrix Components: 3 Angles (θ 12 ; θ 13 ; θ 23 ) 1 CP phase (δ) 2 Mass differences ν ν ν e μ τ U = U U e1 μ1 τ1 U U U e2 μ2 τ2 U U U e3 μ3 τ3 ν ν ν U 1 = 0 0 iδ 0 0 c 13 0 s13e c12 s c23 s s12 c iδ s 23 c23 s13e 0 c atmospheric SK, K2K θ 23 θ atm 45 Large and maximal mixing! - Initial measurement done - Precise measurement under way SNO, solar SK, KamLAND θ 12 θ sol 32

6 Reduction of reactor neutrinos due to oscillations Disappearance Reactor neutrino disappearance Prob. due to θ 13 with the allowed 2σ range in m 23 2 sin 2 2θ 13 > 0.01 with 10 t 14GW 3yr ~ 400 t GW yr (400 t GW yr: a 10(40) ton far detector and a 14(3.5) GW reactor in 3 years)

7 Experimental Method of θ 13 Measurement ν e ν e ν e Oscillations observed as a deficit of anti-neutrinos ν e 1.0 ν e ν e the position of the minimum is defined by Δm 2 13 (~Δm 2 23) Probabilité ν e flux before oscillation observed here 1.27 m P( ν e ν e ) 1 cos 4 θ 13 sin 2 2θ 12 sin 2 12 E ν Distance 2 L sin 2 2θ m 2 sin2 2θ 13 sin 2 13 L E ν 1200 to 1800 meters Find disappearance of ν e fluxes due to neutrino oscillation as a function of energy using multiple, identical detectors to reduce the systematic errors in 1% level.

Reactor Experiment for Neutrino Oscillation RENO Collaboration 11 institutions and 40 physicists in Korea Chonbuk National University Chonnam National University Chung-Ang University Dongshin

8 Reactor Experiment for Neutrino Oscillation RENO Collaboration 11 institutions and 40 physicists in Korea Chonbuk National University Chonnam National University Chung-Ang University Dongshin University GIST Gyeongsang National University Kyungpook National University Sejong University Seoul National University Seoyeong University Sungkyunkwan University Total cost : $10M Start of project : 2006 The first experiment running with both near & far detectors since Aug YongGwang ( 靈光 ) :

YongGwang Nuclear Power Plant Located in the west coast of southern part of Korea ~300 km from Incheon international airport 6 reactors are lined up in roughly equal

9 YongGwang Nuclear Power Plant Located in the west coast of southern part of Korea ~300 km from Incheon international airport 6 reactors are lined up in roughly equal distances and span ~1.3 km Total average thermal output ~16.7GW th (2 nd largest in the world) YongGwang( 靈光 ): = glorious[splendid] light (~spirited) New name: Hanbit

10 Near Detector 70m high Google Satellite View of Experimental Site Reactors 200m high 100m 290m 1,380m 300m Far Detector YongGwang Nuclear Power Plant

5 Inner PMTs: 354 10 PMTs solid angle coverage = ~14% Outer PMTs: ~ 67 10

11 RENO Detector Thick (cm) vessel Material Mass (tons) Target 140 Acrylic (10mm) Gd(0.1%) +LS 15.4 Gamma catcher 60 Acrylic (15mm) LS 27.5 Inner PMTs: PMTs solid angle coverage = ~14% Outer PMTs: ~ PMTs Buffer 70 SUS(5mm) Veto 150 Steel (15mm) Mineral oil 59.2 water total ~460 tons

12 Reactor θ 13 Experiments RENO at Yonggwang, Korea Daya Bay at Daya Bay, China Double Chooz at Chooz, France Experiments Location Thermal Power (GW) Flux Weighted Baselines Near/Far (m) Depth Near/Far (mwe) Target Mass (tons) Statistics per year (GW ton yr) Double Chooz France 8.5 [410/1050] 120/ / RENO Korea / /450 16/ Daya Bay China (576)/ / /

13 The Daya Bay Experiment 13 Measuring neutrino mixing angle θ 13 6 reactor cores, 17.4 GW th Relative measurement 2 near sites, 1 far site Multiple LS detector modules 3km tunnel 20 ton target, 110 ton total weight Good cosmic shielding 250 (860) near (far) sites

14 The Double Chooz Experiment 14 Near Detector L=400 m Depth = 115 m.w.e. (under construction) Far Detector L=1050 m Depth = 300 m.w.e. (collecting data since April 2011) Chooz-B Reactors GW th

15 VETO (Water) Buffer(Mineral Oil) Gamma Cather (LS) Neutrino Target (Gd+LS)

16 Detection of Reactor Antineutrinos γ(0.511mev) e + ν e p n Delayed signal γ Gd γ γ Signal Property 1~8MeV 30μs γ e - γ(0.511mev) prompt signal 30μs E γ ~ 8MeV 8MeV t Use inverse beta decay (v e + p e + + n) reaction process Prompt part: subsequent annihilation of the positron to two 0.511MeV γ Delayed part: neutron is captured ~200µs w/o Gd ~ 30µs w Gd Gd has largest n absorption cross section & emits high energy γ Signal from neutron capture ~2.2MeV w/o Gd ~ 8MeV w Gd Measure prompt signal & delayed signal Delayed coincidence reduces backgrounds drastically

17 Suppresses background a lot! Signal: IBD Pair Prompt signal (S1) n-gd IBD ~30 µs Delayed signal (S2) 8 MeV S1 n-h IBD ~200 µs S2 2.2 MeV

18 Gd-loaded Liquid Scintillator C n H 2n+1 -C 6 H 5 (n=10~14) Recipe of Liquid Scintillator Aromatic Solvent & Flour WLS LAB PPO + Bis-MSB Gd-compound 0.1% Gd+TMHA (trimethylhexanoic acid) High Light Yield : not likely Mineral oil (MO) replace MO and even Pseudocume (PC) Good transparency (better than PC) High flash point : 147 o C (PC : 48 o C) Environmentally friendly (PC : toxic) Components well known (MO : not well known) Domestically available: Isu Chemical Ltd. Solvent-solvent extraction method RCOOH + NH H O RCOONH + H 3RCOONH (aq) + GdCl (aq) Gd(RCOO) O 3 + 3NH 4 Cl 0.1% Gd compounds with CBX (Carboxylic acids; R-COOH) - CBX : TMHA (trimethylhexanoic acid)

19 Liquid Production System ( ~ )

20 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 From SK electronics group

21 RENO Data Taking Status Data taking began on Aug. 1, 2011 with both near and far detectors. (DAQ efficiency : ~95%) A (220 days) : First θ 13 result [11 Aug, 2011~26 Mar, 2012] PRL 108, (2012) B (403 days) : Improved θ 13 result [11 Aug, 2011~13 Oct, 2012] NuTel 2013, TAUP 2013, WIN 2013 C (~800 days) : New θ 13 result Shape+rate analysis (in progress) [11 Aug, 2011~31 Dec, 2013] Total observed reactor neutrino events as of today : ~ 1.5M (Near), ~ 0.15M (Far) Absolute reactor neutrino flux measurement in progress [reactor anomaly & sterile neutrinos] Near Detector A Far Detector B C (new results) Now

22 IBD Event Selection Reject flashers and external gamma rays : Q max /Q tot < 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 µs - E prompt : 0.7 ~ 12.0 MeV, E delayed : 6.0 ~ 12.0 MeV - coincidence : 2 µs < t e+n < 100 µs Multiplicity cut : 100 ms window reject pairs if there is a trigger in the preceding

23 Signature of Reactor Neutrino Event (IBD) Prompt signal (e + ) : 1 MeV 2γ s + e + kinetic energy (E = 1~10 MeV) Delayed signal (n) : 8 MeV γ s from neutron s capture by Gd ~26 µs (0.1% Gd) in LS Observed spectra for Prompt Signal Δm 2 12 = 7.6x10-5 sin 2 (2θ 12 ) = Δm 2 13 = 2.32x10-3 sin 2 (2θ 13 ) = 0.113

24 Observed Spectra for Delayed Signal (n captured by Gd)

25 IBD Candidate Event A candidate for a neutron captured by Gd

26 Backgrounds Accidental coincidence between prompt and delayed signals Fast neutrons produced by muons, from surrounding rocks and inside detector (n scattering : prompt, n capture : delayed) 9 Li/ 8 He β-n followers produced by cosmic muon spallation Accidentals µ Fast neutrons µ 9 Li/ 8 He β-n followers µ γ n p n 9 Li e Gd Gd n Gd

27 Background Events Event time (S1, S2) is not satisfied Veto hit exists

28 Backgrounds After Neutrino 2014, Q max /Q tot cut : allow more accidentals to increase acceptance of signal and minimize any bias to the spectral shape Backgrounds ( /day) Near Far Accidentals 1.82± ± ± ±0.01 Fast Neutron 2.67± ± ± ±0.01 Li/He 9.18± ± ± ±0.22 Cf contamination 0.45± ± ± ±0.26 Total 14.18± ± ± ±0.34 Fraction to total IBD: 3.1 % (Near) 8.1% (Far)

Measured Spectra of IBD Prompt Signal Bkg.: 3.1 % Bkg.: 8.1 % Near Live time = 761.

29 Measured Spectra of IBD Prompt Signal Bkg.: 3.1 % Bkg.: 8.1 % Near Live time = days # of IBD candidate = 457,176 # of background = 14,165 (3.1 %) Far Live time = days # of IBD candidate = 53,632 # of background = 4366 (8.1 %)

$fraction of each isotope determined by reactor core simulation of Westinghouse ANC - φ i (E ν ) : Neutrino spectrum of each fission isotope [* P. Huber, Phys. Rev. C84, 024617 (2011) T. Mueller et al.$

30 Expected Reactor Antineutrino Fluxes Reactor neutrino flux Φ isotopes Pth E = ν ) fi φ isotopes i ( E ) i f E ( ν - P th : Reactor thermal power provided by the YG nuclear power plant - f i : Fission fraction of each isotope determined by reactor core simulation of Westinghouse ANC - φ i (E ν ) : Neutrino spectrum of each fission isotope [* P. Huber, Phys. Rev. C84, (2011) T. Mueller et al., Phys. Rev. C83, (2011)] - E i : Energy released per fission [* V. Kopeikin et al., Phys. Atom. Nucl. 67, 1982 (2004)] i i i

31 Observed Daily Averaged IBD Rate preliminary Good agreement with observed rate and prediction. Accurate measurement of thermal power by reactor neutrinos

32 New θ 13 Measurement by Rate-only Analysis (Preliminary) 2 sin 2θ13 = ± 0.008(stat.) ± 0.010(syst.) Uncertainties (%) sin 2θ13 Statistics (near) (far) = ± σ (Neutrino 2012) σ (TAUP/WIN 2013) 7.8 σ (Neutrino 2014) ± ± (0.15%) Isotope fraction (0.28%) Thermal power (0.20%) Detection efficiency (0.20%) Backgrounds (near) (far) (0.21%) (0.43%) (0.50%)

33 Reactor Neutrinos with neutron captures on H Motivation: 1. Independent measurement of θ 13 value. 2. Consistency and systematic check on reactor neutrinos. * RENO s low accidental background makes it possible to perform n-h analysis. -- low radioactivity PMT -- successful purification of LS and detector materials.

IBD Sample with n-h preliminary n-h IBD Event Vertex Distribution target γ-catcher Near Far Live time(day) 379.663 384.

34 IBD Sample with n-h preliminary n-h IBD Event Vertex Distribution target γ-catcher Near Far Live time(day) IBD Candidate 249,799 54,277 IBD( /day) Accidental ( /day) 25.16± ±0.35 Fast Neutron( /day) 5.62± ±0.08 LiHe( /day) 9.87± ±0.37 S.H. Seo Nantes,

35 Results from n-h IBD sample Very preliminary Rate-only result 2 sin 2θ13 = preliminary (B data set, ~400 days) (Neutrino 2014) ± 0.014(stat.) 2 sin 2θ13 = ± ± 0.014(syst.) 0.015(stat.) ± 0.025(syst.) Removed a soft neutron background and reduced the uncertainty of the accidental background preliminary Near Detector Far Detector 35

36 RENO s Projected Sensitivity of θ 13 Neutrino sin 2θ 13 = 0.101± 0.101± (7.8 σ) 0.008( stat.) ± 0.010( syst.) (~800 days) ± (14 σ) (in 3 years) (13 % precision) (7 % precision) years of data : ±7% - stat. error : ±0.008 ± syst. error : ±0.010 ± shape information ±5% (7 % precision) S.H. Seo 36

37 A Brief History of θ 13 from Reactor Experiments DC: 97 days [ ] R+S DB: 49 days [ ] RENO: 222 days [ ] DC: 228 days [ ] R+S DB: 139 days [ ] DC: n-h [ ] R+S RENO: 403 days [NuTel2013] DC: RRM analysis [ ] R+S DB: 190 days [ ] R+S RENO: 403 days [TAUP2013] DB: 190 days n-h [Moriond2014] DC: 469 days [ν 2014] DB: 563 days [ν 2014] RENO: 795 days [ν 2014] 384 days n-h [ν 2014] RENO 384 days n-h [NOW 2014]

38 Summary New measurement of θ 13 by rate-only analysis 2 sin 2θ13 = ± 0.008(stat) ± 0.010(syst) (preliminary) Shape analysis for m 2 is being finalized (stay tuned) First result on n-h IBD analysis 2 sin 2θ13 = ± 0.014(stat) ± 0.014(syst) (very preliminary) sin 2 (2θ 13 ) to 7% accuracy within 3 years

40 RENO-50

41 Overview of RENO-50 RENO-50 : An underground detector consisting of 18 kton ultralow-radioactivity liquid scintillator & 15, PMTs, at 50 km away from the Hanbit(Yonggwang) nuclear power plant Goals : - Determination of neutrino mass hierarchy - High-precision measurement of θ 12, m 2 21 and m Study neutrinos from reactors, the Sun, the Earth, Supernova, and any possible stellar objects Budget : $ 100M for 6 year construction (Civil engineering: $ 15M, Detector: $ 85M) Schedule : 2015 ~ 2020 : Facility and detector construction 2021 ~ : Operation and experiment

42 Reactor Neutrino Oscillations Short Baseline Long Baseline [Nunokawa & Parke (2005)]

Near Detector (NEAR Detector) Far Detector (FAR Detector) RENO-50 18 kton LS

43 Near Detector (NEAR Detector) Far Detector (FAR Detector) RENO kton LS Detector ~47 km from YG reactors Mt. Guemseong (450 m) ~900 m.w.e. overburden

44 RENO-50 Candidate Site Mt. GuemSeong Altitude : 450 m

45 RENO-50 Candidate Site Mt. GuemSeong Altitude : 450 m Dongshin University RENO-50 Candidate Site

& m 2 31 Precise m 2 21 Large Deficit sin 2 2θ 12 Precise

46 Reactor Neutrino Oscillations at 50 km Neutrino mass hierarchy (sign of m 2 31)+precise values of θ 12, m 2 21 & m 2 31 Precise m 2 21 Large Deficit sin 2 2θ 12 Precise θ 12 Ripple Mass Hierarchy cos sin 21 sin 2 31 sin 2 21

47 Energy Resolution for Mass Hierarchy 3% energy resolution essential for distinguishing the oscillation effects between normal and inverted mass hierarchies

48 Conceptual Design of RENO ktons ultra-low-radioactivity Liquid Scintillation Detector OD PMTs Water Mineral Oil 37 m 32 m 30 m LS (18 kton) PMTs (67%) 30 m 32 m 37 m

49 Technical Challenges KamLAND RENO-50 LS mass ~1 kt 18 kt Energy resolution 6.5%/ E 3%/ E Light yield 500 p.e./mev >1000 p.e./mev LS attenuation length ~16 m ~25 m R&D for 3% energy resolution : - High transparency LS : 15 m 25 m (purification & better PPO) - Large photocathode coverage : 34% 67% (15, PMT) - High QE PMT : 20% 35% (Hamamatsu 20 HQE PMT) - High light yield LS : 1.5 (1.5 g/l PPO 5 g/l PPO)

MC Simulation of RENO-50 R&D with optimization of detector design by a MC study Increase of photosensitive area up to ~60% using 15,000 20 PMTs to maximize the light collection

50 MC Simulation of RENO-50 R&D with optimization of detector design by a MC study Increase of photosensitive area up to ~60% using 15, PMTs to maximize the light collection PMT arrangement scheme. - Barrel : 50 raw * 200 column - Top & Bottom: 2500 PMTs for each region Target : Acrylic, 30m*30m Buffer : Stainless-Steel, 32m*32m Veto : Concrete, 37m*37m

51 RENO-50 PMT Arrangement Top & Bottom Barrel 55 cm 60 cm 55 cm 57 cm

52 High QE PMTs Use of high, 35%, quantum efficiency PMTs in development Hamamatsu HQE PMT, R12860

53 LS Purification Scheme Develop efficient methods for mass purification of radioactivity in LS Radioisotopes Source Typical concentration Required concentration Strategy for reduction 14 C Cosmogenic bombardment of 14 N 14 C/ 12 C C/ 12 C Use of LAB from petroleum derivative (old carbon) 7 Be Cosmogenic bombardment of 12 C Bq/t-carbon <10-6 Bq/t-carbon Distillation, or underground storage of scintillator 238 U 232 Th Dust or surface contamination g/g-dust <10-16 g/g LAB Water extraction +Distillation +Filtration +ph control 40 K Dust or contamination in fluor g/g-dust <10-13 g/g in LAB <10-11 g/g in fluor Water extraction 222 Rn Air and emanation from material 100 Rn atom/t-lab 1 Rn atom/t-lab Nitrogen stripping From a Borexino paper

LS Purification & Test Facility Develop a test purification facility of ~5 ton LS and build a water shield tank of scintillation detector to measure radioactivity in LS - Water extraction: removal of

54 LS Purification & Test Facility Develop a test purification facility of ~5 ton LS and build a water shield tank of scintillation detector to measure radioactivity in LS - Water extraction: removal of polar and charged impurities - Vacuum distillation: removal of radioactive and chemical impurities - Filtration with a 0.05 mm Teflon filter: removal of particulates (* suspended dust particles that may contain U, Th and K) - Nitrogen stripping: removal of water and dissolved noble gases of Kr Test facility of Borexino Ref. J.B. Benzinger et al., NIM A 417, (1998)

55 RENO-50 vs. KamLAND RENO-50 (50 km) KamLAND (180 km) Figure of Merit Oscillation Reduction Reactor Neutrino Flux 80% 13 6 φ 0 [6 reactors] 40% φ 0 [55 reactors] Detector Size Syst. Error on ν Flux Error on sin 2 θ kton ~ 0.3% < 1% 1 kton 3% 5.4% (50 km / 180 km) 2 13 Observed Reactor Neutrino Rate - RENO-50 : ~ 15 events/day Determination of mass ordering: - KamLAND : ~ 1 event /day ~ 3σ with 5 year data

56 2012 Particle Data Book (±2.8%) (±2.7%) (±3.1%) ( %) (±13.3%) sin 2 θ 12 = 0.312±0.017 (±5.4%) m 21 2 / m 31(32) Precise measurement of θ 12, m 2 21 and m δ sin θ 2 sin θ < 1.0% 1 ( σ ) ( 5.4%) δ m m < 1.0% 1 ( σ ) ( 2.7%) δ m m < 1.0% 1 ( σ ) ( 5.2%)

57 Additional Physics with RENO-50 Neutrino burst from a Supernova in our Galaxy - ~5,600 events (@8 kpc) (* NC tag from 15 MeV deexcitation γ) - A long-term neutrino telescope Geo-neutrinos : ~ 1,000 geo-neutrinos for 5 years - Study the heat generation mechanism inside the Earth Solar neutrinos : with ultra low radioacitivity - MSW effect on neutrino oscillation - Probe the center of the Sun and test the solar models Detection of J-PARC beam : ~200 events/year Neutrinoless double beta decay search : possible modification like KamLAND-Zen

58 Schedule 2015 : Group organization Detector simulation & design Geological survey 2016 ~ 2017 : Civil engineering for tunnel excavation Underground facility ready Structure design PMT evaluation and order, Preparation for electronics, HV, DAQ & software tools, R&D for liquid scintillator and purification 2018 ~ 2020 : Detector construction 2021 ~ : Data taking & analysis

59 Summary Longer baseline (~50 km) reactor experiments is under pursuit to determine the mass hierarchy in 3σ for 5 years of data-taking, and to perform high-precision (<1%) measurements of θ 12, m 2 21, & m Domestic and international workshops held in 2013 to discuss the feasibility and physics opportunities An R&D funding (US $ 2M in next 3 years) will be given by the Samsung Science & Technology Foundation. SNU & CNU start doing various R&D works A proposal have been submitted to obtain full funding. Thanks for your attention!

62 Comparisons 18

63 θ 13 from Reactor and Accelerator Experiments First hint of δ CP combining Reactor and Accelerator data Best overlap is for Normal hierarchy & δ CP = - π/2 Is Nature very kind to us? Are we very lucky? Is CP violated maximally? Strong motivation for anti-neutrino runs and precise measurements of θ 13 Courtesy C. Walter (T2K Collaboration) Talk at Neutrino 2014

64 Expected Energy Resolution PMT coverage : 67% (15, PMTs) PMT coverage : 67% (15, PMTs) + Attenuation length : 25 m + QE : 35%

A Large Liquid Scintillator Detector for Neutrino Mass Hierarchy : RENO-50

A Large Liquid Scintillator Detector for Neutrino Mass Hierarchy : RENO-50 International Meeting for Large Neutrino Infrastructures Ecole Architecture Paris Val de Seine, APPEC, 23-24 June, 2014 Soo-Bong