Observation of Reactor Electron Antineutrino Disappearance & Future Prospect

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1 Observation of Reactor Electron Antineutrino Disappearance & Future Prospect Soo-Bong Kim (KNRC, Seoul National University) at Kyungpook National Univ., November 1, 01

2 Birth of Neutrino Physics in trouble with b decay - Energy & momentum are not conserved - Observed continuous b spectra - Total spin is not conserved b decay 14 C 14 N + e S=0 S=1 S=1/ Bohr: Energy and momentum may not be conserved in b decay? Wolfgang Pauli s introduction of an imaginary particle (1931) Neutrino : Undetectable massless neutral fermion (Weakly interacting) Discovery of Neutrino : Reines & Cowan (1957)

3 Tiny Neutrino Mass GUT SM mass kg E=mc kg 10-7 kg Neutrino mass & oscillation : window for new physics beyond the standard model

4 Neutrino Oscillation PMNS Neutrino Mixing Angles (1998) ~80% P( e Reactor Antineutrino Oscillation ) e 1. m 1sin 7 13sin E 31 L Solar Neutrinos (?) (01) 3 3 Atmospheric Neutrinos ~100%

5 RENO Collaboration (1 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 YongGwang ( 靈光 ) : Total cost : $10M Start of project : 006 The first experiment running with both near & far detectors from Aug. 011

6 Summary of RENO s History &Status RENO began design, tunnel excavation, and detector construction in March 006 RENO was the first reactor neutrino experiment to search for 13 with both near & far detectors running, from the early August 011. RENO started to see a signal of reactor neutrino disappearance from the late 011. RENO submitted the first result to PRL on April, and it appeared on May 11, 01. sin ( stat) 0.019( syst) Data-taking & data-analysis in a steady state. Shape analysis and background reduction under progress.

7 Definitive measurement of the last, smallest neutrino mixing angle 13 based on the disappearance of reactor electron antineutrinos [citation : 16] Open a bright window for CP violating phase & mass hierarchy CERN Courier

8 Included in a new edition of Particle Data Listing this year

9

10 Efforts for Finding 13 Chooz (003) & Palo Verde (000): No signal sin ( 13 ) < 0.1 at 90% C.L. TK :.5 s excess (011) 0.03 sin ( < sin 13 ) = ( ) < 0.8 at 90% (δ CP C.L. =0 for for N.H.) 0.04 sin ( < sin 13 ) = ( ) < 0.34 at 90% (δ CP C.L. =0 for for I.H.) (Neutrino 01) MINOS : 1.7 s excess (011) 0 < sin ( 13 ) < 0.1 at 90% C.L. for N.H < sin ( 13 ) < 0.19 at 90% C.L. for I.H. Double Chooz : 1.7 s measurement (011) Daya Bay (Mar ) 5. s observation sin ( 13 ) = ± 0.016(stat.)±0.005(syst.) 0.010(stat.)±0.005(syst.) (Neutrino 01) RENO (Apr.. 01) 4.9 s observation sin ( 13 ) = ± 0.013(stat.)±0.019(syst.) sin ( 13 ) = ± 0.041(stat.) 0.030(stat.) ± 0.030(syst.) 0.05(syst.) (Neutrino 01)

11 sin ( 13 ) Measurements (5. s) (4.9 s) Janet Conrad, Physics 5, 47, April 3, (01) Double-CHOOZ, arxiv: , (01)

12 13 from Reactor and Accelerator Experiments * Reactor m 31 L 4 m P ee 1sin 13sin cos 13sin 1sin 4E 4E - Clean measurement of 13 with no matter effects * Accelerator - mass hierarchy + CP violation + matter effects Precise measurement of 13 1 L Complementary : Combining results from accelerator and reactor based experiments could offer the first glimpse of CP.

13 RENO Experimental Setup Near Detector Far Detector

14 RENO Detector 354 ID +67 OD 10 PMTs Target : 16.5 ton Gd-LS, R=1.4m, H=3.m Gamma Catcher : 30 ton LS, R=.0m, H=4.4m Buffer : 65 ton mineral oil, R=.7m, H=5.8m Veto : 350 ton water, R=4.m, H=8.8m

15 Summary of Detector Construction : Start of the RENO project ~ : Civil construction including tunnel excavation ~ : Detector structure & buffer steel tanks completed : Acrylic containers installed ~ : PMT test & installation : Detector closing/ Electronics hut & control room built : Installation of DAQ electronics and HV & cabling ~ 06 : Dry run & DAQ debugging ~ 07 : Liquid scintillator production & filling : Detector operation & commissioning : Start data-taking

16 PMT Mounting (010. 8~10)

17 PMT Mounting (010. 8~10)

18 Detector Closing (011. 1) Near : Jan. 1, 011 Far : Jan. 4, 011

19 Observed Daily Averaged IBD Rate A new way to measure the reactor thermal power remotely!!!

20 Reactor Antineutrino Disappearance R Far observed Far expected ( stat) 0.014( syst) A clear deficit in rate (8.0% reduction) Consistent with neutrino oscillation in the spectral distortion sin s significant signal ( stat.) 0.019( syst.) Near detector: 1.% reduction Far detector: 8.0% reduction

21 Future Plan for Precision Measurement of 13 sin ( stat.) (4.9 s) (30 days) (3 years) 0.019( syst.) 3 years of data : ±0.01 for the total measurement error - statistical error : ±0.013 (~00 days) ± systematic error : ±0.019 ±0.014 (background reduction) ±0.010 (reduction of reactor uncertainty + shape analysis) ±0.005 (reduction of detection efficiency uncertainty) Remove backgrounds Spectral shape analysis (with precise energy calibration) Reduce uncertainties of reactor neutrino flux & detector efficiency

22 Summary RENO was the first experiment to take data with both near and far detectors, from August 1, 011. RENO observed a clear disappearance of reactor antineutrinos. R ( stat) 0.014( syst) RENO measured the last, smallest mixing angle 13 unambiguously that was the most elusive puzzle of neutrino oscillations. sin ( stat) 0.019( syst) A surprisingly large value of 13 will strongly promote the next round of neutrino experiments to find the CP phase, and could reduce the costs by reconsideration of their designs.

23 Data-Taking & Data Set Data taking began on Aug. 1, 011 with both near and far detectors. Data-taking efficiency Data-taking efficiency > 90%. Trigger rate at the threshold energy of 0.5~0.6 MeV : 80 Hz Data-taking period (0 430 days) Aug. 011 ~ Oct. 01 A candidate for a neutron capture by Gd

24 Energy Calibration Cs 137 (66 kev) -Near Detector -Far Detector Ge 68 (1,0 kev) Co 60 (,506 kev) Cf 5 (./7.96 MeV)

25 Detection of Reactor Antineutrinos (prompt signal) γ(0.511mev) (delayed signal) ~180 ms + p D + (. MeV) ~8 ms (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

26 Gd Loaded Liquid Scintillator C n H n+1 -C 6 H 5 (n=10~14) Recipe of Liquid Scintillator Aromatic Solvent & Flour WLS Gd-compound LAB PPO + Bis-MSB 0.1% Gd+(TMHA) 3 (trimethylhexanoic acid) Steady properties of Gd-LS Stable light yield (~50 pe/mev) & transparency Stable Gd concentration (~0.11%)

27 IBD Event Signature and Backgrounds IBD Event Signature Prompt signal (e + ) : 1 MeV s + e + kinetic energy (E = 1~10 MeV) Delayed signal (n) : 8 MeV s from neutron s capture by Gd ~6 ms (0.1% Gd) in LS Prompt Energy Delayed Energy Backgrounds Random coincidence between prompt and delayed signals (uncorrelated) 9 Li/ 8 He b-n followers produced by cosmic muon spallation Fast neutrons produced by muons, from surrounding rocks and inside detector (n scattering : prompt, n capture : delayed)

28 Spectra & Capture Time of Delayed Signals Far Detector Observed spectra of IBD delayed signals t = 6. ± 0.3 msec Near Detector t = 6. ± 0.1 msec

29 Detector Stability

30 Expected Reactor Antineutrino Fluxes Reactor neutrino flux isotopes Pth E ) fi isotopes i ( E ) i f E ( - 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 - i (E ) : Neutrino spectrum of each fission isotope [* P. Huber, Phys. Rev. C84, (011) T. Mueller et al., Phys. Rev. C83, (011)] - E i : Energy released per fission [* V. Kopeikin et al., Phys. Atom. Nucl. 67, 198 (004)] i i i

31 Observed Daily Averaged IBD Rate R R1 R5 R4 R6 R5

32 Contribution of Reactor to Neutrino Flux at Near & Far Detectors Reactor # Far ( % ) Near (% ) Accurate measurement of baseline distances to a precision of 10 cm using GPS and total station Accurate determination of reduction in the reactor neutrino fluxes after a baseline distance, much better than 0.1%

33 Problems in Neutrino Physics (1) High precision measurement of neutrino oscillations : Why so large (compared to the quark mixing)? Precise values of mixing angles and mass difference? CP violating phase? (Asymmetry of matter and anti-matter) Dirac or Majorana? : Neutrinoless double beta decay?

34 Problems in Neutrino Physics () Neutrino mass hierarchy : ( m 31(3) m 1 > 0 i.e. m > m 1 ) Sign of m 31(3)? [ m 3 m > m 1 (normal; NH) or m > m 1 m 3 (inverted; IH) ] * m atm m 31(3) ( m 31 m 3 ) * m sol m 1 * m sol / m atm 0.03, m atm m sol > 0

35 Problems in Neutrino Physics (3) Neutrino masses : Why so small? How to extend the SM? (1) NH ( m 3 m > m 1 ) : m (3) = (m 1 + m 1(31) ) 1/ m ( m sol ) 1/ ev m 3 ( m atm ) 1/ ev () IH ( m > m 1 m 3 ) : m (1) = IH (m 3 + m 3(13) ) 1/ m m 1 ( m atm ) 1/ ev (3) QD ( m 1 m m 3 ) : NH m i ( m atm ) 1/ m 1 m m ev

36 P(e --> e ) RENO-50 Large 1 neutrino oscillation effects at 50 km + 5kton liquid scintillator detector RENO can be used as near detectors. Precise reactor neutrino fluxes Negligible contribution from other nuclear power plants. P R e e 4 cos 13sin 1sin 1 1 sin 13sin 1 cos 31 sin 1 1 sin 31 sin 1 1. Reactor Neutrino Oscillation Reactor Neutrino Oscillation RENO KamLAND L~50km experiment could be a natural extension of current RENO 13 experiment. (018 ~ ) RENO Competition with Daya L(km) Bay-II Timely support and start are important!

37 RENO-50 vs. KamLAND RENO-50 RENO-50 is dedicated to the YG power plant. (negligible contribution from the other nuclear power plants) RENO can be used as near detectors. Precise reactor neutrino fluxes : systematic error from ~3% to ~0.1% KamLAND uses the entire Japanese nuclear power plants as a source.

38 1 st m 1 Maximum (L~50km) ; precise value of 1 & m 1 + mass hierarchy (m 31) P R e e 4 cos 13sin 1sin 1 1 sin 13sin 1 cos 31 sin 1 1 sin 31 sin 1 sin 1 Large Deficit Precise 1 Ripple Mass Hierarchy cos 1 31sin 1 sin 31sin 1

39 5000 tons ultra-low-radioactivity Liquid Scintillation Detector RENO RENO m 8.8 m RENO OD PMTs Water 5.4 m 8.4 m 5 m 0 m LAB (5 kton) PMTs 0 m KamLAND 5 m

40 RENO-50 vs. KamLAND RENO-50 (50 km) KamLAND (180 km) Figure of Merit Oscillation Reduction Reactor Neutrino Flux 80% [6 reactors] 40% 53 0 [53 reactors] Detector Size Syst. Error on Flux Error on sin 1 5 kton ~ 0.3% ~1% 1 kton 3% 5.4% (50 km / 180 km) 13

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

42 Physics with RENO-50 (1) Precise measurement of 1 and m 1 sin sin 1 1 ~ 1.0% 1s ( 5.4%) in a year m m 1 1 ~ 1.0% 1s (.6%) in ~3 years Determination of mass hierarchy (sign of m 31 or m 3) - Quite challenging : requires extremely good energy resolution - Plan B : an additional 00 ton detector at ~10 km (L : 300 m km + 10 km + 50 km) Neutrino burst from a Supernova in our Galaxy - ~1500 events (@8 kpc) - A long-term neutrino telescope

43 Physics with RENO-50 () Geo-neutrinos : ~ 300 geo-neutrinos for 5 years - Study the heat generation mechanism inside the Earth Solar neutrinos : with ultra low radioacitivity - Matter effects on neutrino oscillation - Probe the center of the Sun and test the solar models Reactor physics : non-proliferation Detection of J-PARC beam : ~10 events/year Test of non-standard physics : sterile/mass varying neutrinos

44 Physics with RENO-50 (3) Search for neutrinoless double beta decay RENO-50 Water 5 m 0 m LAB (5 kton) PMTs 0 m 5 m

45 Closing Remarks Neutrino physics has gone through remarkable progress during the last two decades. RENO, the first Korean neutrino detector, was the first secondgeneration reactor experiment to search for the last, remaining neutrino mixing angle with both near and far detectors in operation. RENO observed a clear disappearance of reactor antineutrinos, and performed a definitive measurement of 13. A surprisingly large value of 13 will strongly promote the next round of neutrino experiments to find the CP phase and determine the mass hierarchy. RENO has elevated the Korean neutrino physics to the worldleading class level.

46 RENO will continue data-taking for next 3~4 more years, reaching its sensitivity limit, in order to obtain a precise measurement of 13. Korean reactors can be freely used as an intense neutrino source to study the neutrino properties. We need a next, flagship neutrino experimental program continuously to play a world-leading role in neutrino physics. RENO-50, a multi-purpose neutrino detector, should be pursued to perform high-precision measurements of 1 and m 1, determine the mass hierarchy, and detect neutrinos from the astrophysical sources. A competing project may be Daya Bay-II. Timely start of RENO-50 is quite necessary. Thank you!