Current Results from Reactor Neutrino Experiments

Transcription

1 Current Results from Reactor Neutrino Experiments Soo-Bong Kim (KNRC, Seoul National University) Tsukuba Global Science Week (TGSW015), Tsukuba, Sep. 8-30, 015

2 Neutrino Physics with Reactor 1956 Discovery of (anti)neutrino Savannah River 003 Observation of reactor neutrino oscillation ( 1 & m 1 ) KamLAND 01 Measurement of the smallest mixing angle 13 IBD rate ( /day) Near Detector Expected with no oscillation Expected with oscillation (best fit) Far Detector Aug 01 Jan 01 July 013 Jan 013 July 014 Jan

3 Reactor Neutrinos Reactor Neutrinos Nuclear Power Plants ~ /sec Cost-free, intense, low-energy & well-known neutrino source! Hanbit

4 Reactor 13 Experiments RENO at Yonggwang, Korea Daya Bay at Daya Bay, China Double Chooz at Chooz, France

5 13 Reactor Neutrino Detectors MO LS Gd-LS H O

6 RENO Collaboration Reactor Experiment for Neutrino Oscillation (11 institutions and 40 physicists) 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 YongGwang ( 靈光 ) : Total cost : $10M Start of project : 006 The first experiment running with both near & far detectors from Aug. 011

7 RENO Experimental Set-up 10 m.w.e. Near Detector Far Detector 450 m.w.e.

8 RENO Status Data taking began on Aug. 1, 011 with both near and far detectors. (DAQ efficiency : ~95%) A (0 days) : First 13 result [11 Aug, 011~6 Mar, 01] PRL 108, (01) A Near Detector 1400 days of data B (403 days) : Improved 13 result [11 Aug, 011~13 Oct, 01] NuTel 013, TAUP 013, WIN 013 C (~800 days) : New result Shape+rate analysis ( 13 and m ee ) [11 Aug, 011~31 Dec, 013] 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] B Far Detector C (new results) Now

9 Detection of Reactor Antineutrinos (prompt signal) γ(0.511mev) (delayed signal) ~180 s + p D + (. MeV) ~8 s (0.1% Gd) + Gd Gd + s (8 MeV) e - Neutrino energy measurement ν e e + p γ(0.511mev) prompt signal Delayed signal γ γ Gd n γ 30μs γ E ~8MeV

10 New RENO Results ~800 days of data New measured-value of 13 from rate-only analysis Observation of energy dependent disappearance of reactor neutrinos to measure m ee and 13 (work in progress) Observation of an excess at 5 MeV in reactor neutrino spectrum

11 Improvements after Neutrino 014 Relax Q max /Q tot cut : allow more accidentals to increase acceptance of signal and minimize any bias to the spectral shape More precisely observed spectra of Li/He background - reduced the Li/He background uncertainty based on an increased control sample More accurate energy calibration - best efforts on understanding of non-linear energy response and energy scale uncertainty Elaborate study of systematic uncertainties on a spectral fitter - estimated systematic errors based on a detailed study of spectral fitter in the measurement of m ee

12 Neutron Capture by Gd

13 Measured Spectra of IBD Prompt Signal Bkg.: 5.6 % Bkg.: 1.0 % Near Live time = days # of IBD candidate = 470,787 # of background = 6,375 (5.6 %) Far Live time = days # of IBD candidate = 5,50 # of background = 6,9 (1.0 %)

14 Observed Daily Averaged IBD Rate IBD rate ( /day) Near Detector Expected with no oscillation Expected with oscillation (best fit) preliminary Far Detector Aug 01 Jan 01 July 013 Jan 013 July 014 Jan Good agreement with observed rate and prediction. Accurate measurement of thermal power by reactor neutrinos

15 Observed vs. Expected IBD Rates - Good agreement between observed rate & prediction - Indication of correct background subtraction

16 New 13 Measurement by Rate-only Analysis (Preliminary) sin θ (stat.) 0.008(syst.) Uncertainties sources Statistics (near) (far) Systematics (near) (far) Uncertainties (%) Errors of sin 13 (fraction) 0.1 % 0.54 % 0.94% 1.06% Reactor 0.9 % (39.5 %) Detection efficiency 0. % (45.7 %) Backgrounds (near) (far) 0.14 % 0.51 % (86.4 %)

17 Observation of an excess at 5 MeV ~.5% ~.5%

18 Correlation of 5 MeV Excess with Reactor Power two or three reactors are off All the six reactors are on 5 MeV excess has a clear correlation with reactor thermal power! A new reactor neutrino component!! ** Recent ab initio calculation [D. Dwyer and T.J. Langford, PRL 114, 0150 (015)] : The excess may be explained by addition of eight isotopes, such as 96 Y and 9 Rb

19 The 5 MeV Excess Seen at Double-Chooz and Daya Bay Daya Bay, ICHEP 014 Double Chooz, Neutrino 014

20 Why n-h IBD Analysis? Motivation: 1. Independent measurement of 13 value.. Consistency and systematic check on reactor neutrinos. * RENO s low accidental background makes it possible to perform n-h analysis. -- low radio-activity PMT -- successful purification of LS and detector materials.

21 IBD Sample with n-h preliminary n-h IBD Event Vertex Distribution target -catcher Near Far Live time(day) IBD Candidate 49,799 54,77 IBD( /day) Accidental ( /day) 5.16± ±0.35 Fast Neutron( /day) 5.6± ±0.08 LiHe( /day) 9.87± ±0.37

22 Very preliminary Rate-only result sin θ13 Results from n-h IBD sample preliminary (B data set, ~400 days) (Neutrino 014) 0.014(stat.) sin θ (syst.) 0.015(stat.) 0.05(syst.) Removed a soft neutron background and reduced the uncertainty of the accidental background preliminary Near Detector Far Detector

23 Reactor Neutrino Oscillations ν e ν e ν e Oscillations observed as a deficit of anti-neutrinos ν e Probability ν e 1.0 ν e ν e flux before oscillation observed here the position of the minimum is defined by Δm ee sin θ 13 Distance 100 to 1800 meters cos Δ

24 Energy Calibration from -ray Sources

25 B1 Energy Spectrum (Near & Far)

26 Energy Scale Difference between Near & Far Energy scale difference < 0.15%

27 Far/Near Shape Analysis for m ee (work in progress)

28 Results from Spectral Fit (work in progress) ee m [ (stat) 0.17(syst) ] x10-3 ev sin θ (stat ) 0.007(syst )

29 Systematic Errors of 13 & m ee (work in progress) sin θ (stat ) 0.007(syst ) (± 11 %) ee m [ (stat) 0.17(syst) ] x10-3 ev (± 10 %) Uncertainties sources Statistics (near) (far) Uncertainties (%) Errors of sin 13 Errors of m ee 0.1 % 0.54 % Total Systematics 0.94 % 1.06 % (x 10-3 ev ) Reactor 0.9 % (34. %) Detection efficiency 0. % (34. %) Energy scale diff %* (15.6 %) 0.07 Backgrounds (near) (far) (* tentative) 0.14 % 0.51 % (8. %) 0.15

30 Observed L/E Dependent Oscillation (work in progress)

31 Double Chooz Results (460 days) : No near site detector until Spectral analysis for n-gd & n-h samples Reactor-off data for direct measurement of backgrounds R+S : sin 13 =

32 Daya Bay Results (61 days) Rate+Spectral analysis for n-gd sample Rate analysis for n-h sample

33 Projected Sensitivity of 13 & m ee NDM 015 sin (5 % precision) (~800 days) (5 years of data) * Expected precision of m ee ~ ev (~ 4% precision) (5 % precision) (sensitivity goal of 13 ) 33

34 Future Prospects on 13 & m ee Precision dominated by statistics Continued efforts on improving systematics Expected ultimate precision : Experiments (sin 13 ) m ee ) [ 10-3 ev ] Daya Bay ±0.003 (±3%) ±0.07 (±3%) RENO ±0.005 (±5%) ±0.1 (±4%) Double Chooz ±0.010 (±10%) 34

35 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/ Is Nature very kind to us? Are we very lucky? Is CP violated maximally? Strong motivation for anti-neutrino run and precise measurement of θ 13 (TK: PRL 11, 06180, 014) 35

36 Summary Observed an excess at 5 MeV in reactor neutrino spectrum New measurement of 13 by rate-only analysis sin θ (stat ) 0.008(syst ) (preliminary) Observation of energy dependent disappearance of reactor neutrinos and our first measurement of m ee sin θ13 ee m [ (stat 0.19(stat) ) 0.007(syst 0.17(syst) ] x10-3 ) ev (work in progress) Measurement of 13 from on n-h IBD analysis sin θ (stat ) 0.014(syst ) (preliminary) sin( 13 ) to 5% accuracy m ee to ev (4%) accuracy within 3 years

37 Overview of RENO-50 RENO-50 : An underground detector consisting of 18 kton ultralow-radioactivity liquid scintillator & 15,000 0 PMTs, at 50 km away from the Hanbit(Yonggwang) nuclear power plant Goals : - Determination of neutrino mass ordering - High-precision measurement of 1, m 1 and m ee - 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 : 015 ~ 00 : Facility and detector construction 01 ~ : Operation and experiment

38 Determination of Neutrino Mass Hierarchy Reactor experiments: JUNO and RENO-50 - Subdominant oscillation pattern of m 31 - Large liquid scintillator detector with a baseline of ~50 km - Extraordinary energy resolution (<3% at 1 MeV) Long baseline beam experiments: TK, NOvA, THK and LBNE - Matter effects of neutrino oscillation - Small value of m 3 /E & long baseline L Atmospheric neutrino experiments with Mton scale : HK, LBNE, MEMPHIS, PINGU and INO - Matter effects of neutrino oscillation - Small value of m 3 /E & long baseline L

39 Reactor Neutrino Oscillations at 50 km Neutrino mass hierarchy (sign of m 31)+precise values of 1, m 1 & m ee Precise m 1 Large Deficit sin 1 Precise 1 Ripple Mass Hierarchy cos 1 31sin 1 sin31sin 1

40 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

41 Various Physics with RENO-50 Precise (<1%) measurement of 1, m 1 and m ee - Provide an interesting test for unitarity - Essential for the future discoveries Neutrino burst from a Supernova in our Galaxy - ~5,600 events (@8 kpc) (* NC tag from 15 MeV deexcitation ) - Study the core collapsing mechanism with neutrino cooling 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 to study the metallicity problem Detection of J-PARC beam : ~00 events/year

42 J-PARC neutrino beam Dr. Okamura & Prof. Hagiwara

43 Thanks for your attention!

44 Experimental site 44