Results and Prospects of Neutrino Oscillation Experiments at Reactors

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6! 5! 4! 1 2! 3!! Results and Prospects of Neutrino Oscillation Experiments at Reactors Survival Probability 1 0.8 0.6 0.4 0.2 0 20 4! 15 Karsten M.

1 6! 5! 4! 1 2! 3!! Results and Prospects of Neutrino Oscillation Experiments at Reactors Survival Probability ! 15 Karsten M. Heeger University of Wisconsin Data - BG - Geo & e 99.73% C.L. Expectation based on osci. parameters best fit determined by KamLAND L 0 /E &e (km/mev) Karsten Heeger, Univ. of Wisconsin 10 5 ev 2 La and tan Thuile, 2 θ 12 = 0.52 March , $# ) 2 (ev 2 21 $m KamLAND 95% C.L. 99% C.L % C.L. best fit Solar 95% C.L. 99% C.L. 2! 1! tan " 12 $# FIG. 2: Allowed region for neutrino oscillation parameters from KamLAND and solar neutrino experiments. The side-panels show the χ 2 -profiles for KamLAND (dashed) and solar experiments (dotted) individually, as well as the combination of the two (solid). we also expect geo-neutrinos. We observe 1609 events. Figure 1 shows the prompt energy spectrum of selected electron anti-neutrino events and the fitted backgrounds. The unbinned data is assessed with a maximum likelihood fit to two-flavor neutrino oscillation (with θ 13 = 0), simultaneously fitting the geo-neutrino contribution. The method incorporates the absolute time of the event to account for time variations in the reactor flux and includes Earth-matter oscillation effects. The best-fit is shown in Fig. 1. The joint confidence intervals give m 2 21 = (stat) (syst) 10 5 ev 2 and tan 2 θ 12 = (syst) for tan2 θ 12 <1. A 0.07 (stat)+0.10 scaled reactor spectrum without distortions from neutrino oscillation La Thuile, is excluded at more March than 5σ. 3, An independent 2009 analysis using cuts similar to Ref. [2] finds m 2 21 = ! 0.20 The allowed contours in the neutrino oscillation parame- N osc /N no_osc Events / 0.2 MeV KamLAND data best-fit osci. accidental Data - BG - best-fit osci. Reference Geo " e [8] C(!,n) O 40 best-fit Geo " e 20 best-fit osci. + BG + best-fit Geo " e E p (MeV) 1 FIG. 3: The low-energy region of the ν e spectrum relevant for geoneutrinos. The main panel shows the data with the fitted background 0.9 and geo-neutrino contributions; the upper panel compares the background and 0.8reactor ν e subtracted data to the number of geo-neutrinos for the decay chains of U (dashed) and Th (dotted) calculated from a geological 0.7reference model [8]. Survival Probability Data - BG - Geo! e Expectation based on osci. parameters determined by KamLAND Baseline (km) L 0 /E!e (km/mev) FIG. 4: Ratio of the background and geo-neutrino subtracted ν e spectrum to the expectation for no-oscillation as a function of L 0/E. L 0 is the effective baseline taken as a flux-weighted average (L 0 = 180 km); the energy bins are equal probability bins of the best-fit including all backgrounds (see Fig. 1). The histogram and curve show the expectation accounting for the distances to the indi- 4

Neutrino Physics at Reactors Next - Discovery and precision measurement of θ 13 2008 - Precision

of reactor antineutrino disappearance 1995 - Nobel Prize to Fred Reines at UC Irvine KamLAND

and Europe 1956 - First observation of (anti)neutrinos Chooz Savannah River Chooz Past Reactor

2 Neutrino Physics at Reactors Next - Discovery and precision measurement of θ Precision measurement of Δm12 2 Daya Bay Evidence for spectral distortion First observation of reactor antineutrino disappearance Nobel Prize to Fred Reines at UC Irvine KamLAND 1980s & 1990s - Reactor neutrino flux measurements in U.S. and Europe First observation of (anti)neutrinos Chooz Savannah River Chooz Past Reactor Experiments Hanford Savannah River ILL, France Bugey, France Rovno, Russia Goesgen, Switzerland Krasnoyark, Russia Palo Verde Chooz, France

~3000 events 335 days 5 ton target ν e +

3 Past Oscillation Searches with Reactor Antineutrinos Best Limit from Chooz thermal power 8.5 GW 1 km baseline ν e ν e νe νe ν e ν e ~3000 events 335 days 5 ton target ν e + p e + + n No evidence for oscillation Absolute measurement with 1 detector

4 Measuring Reactor Antineutrinos in Japan Japanese Reactors Kashiwazaki Reactor Antineutrinos Takahama Ohi Japan Kamioka 55 reactors 235 U: 238 U: 239 Pu: 241 Pu = 0.570: 0.078: : ~ 200 MeV per fission ~ 6 ν e per fission reactor ν flux at KamLAND ~ 2 x ν ~ 6 x 10 6 /cm 2 e /GW th -sec /sec

5 KamLAND Antineutrino Detector ν e + p e + + n n light from the e gives a measu E p + E n MeV, E νe through inverse β-decay liquid scintillator target: - proton rich > protons - good light yield

KamLAND 2003: First Direct Evidence for Reactor ν e Disappearance Reactor Neutrino Physics 1956-2003 PRL 90:021802 (2003) Observed ν e 54 events No-Oscillation 86.8 ± 5.

6 KamLAND 2003: First Direct Evidence for Reactor ν e Disappearance Reactor Neutrino Physics PRL 90: (2003) Observed ν e 54 events No-Oscillation 86.8 ± 5.6 events Background 1 ± 1 events Livetime: ton-yr Japan Thermal Power Flux (µw/cm 2 ) mean, flux-weighted reactor distance ~ 180km Many reactors, far away Distance (km) Survival Evis >2.6 MeV

7 KamLAND s Energy spectrum 2005: adds substantial information Evidence of Spectral Distortion in Energy Spectrum analysis threshold best fit χ 2 =24/17 Phys.Rev.Lett.94:081801,2005 Observed ν e 258 events No-Oscillation ± 23.7 (syst.) Background 17.8 ± 7.3 events Livetime: ton-yr fiducial volume syst.: 4.7% total systematics = 6.5% Spectral Distortions: A unique signature of neutrino oscillation! Simple, rescaled reactor spectrum is excluded at 99.6% CL(χ 2 =37.3/18) Next Step: Reduce systematic error with improved calibrations.

Neutrinos + KamLAND 2005 (ν e rate+spectrum) Agreement between

8 Measuring θ12 and Δm12 2 with Solar ν and KamLAND Solar Neutrinos Solar Neutrinos + KamLAND 2003 (ν e rate) Solar Neutrinos + KamLAND 2005 (ν e rate+spectrum) Agreement between oscillation parameters for ν and ν Beginning of precision neutrino physics

9 KamLAND 2008: Precision Measurement of Neutrino Oscillation Parameters Phys.Rev.Lett.100:221803,2008 increased livetime increased livetime: 1491 days lowered analysis threshold modified analysis to enlargen the fiducial volume Rprompt, Rdelayed < 6.0m KamLAND 2008 data set March 9, 2002 May 12, 2007 improved calibration reduced uncertainty in 13 C(α,n) 16 O backgrounds reduced systematics in target protons by calibrating fiducial volume FV

10 calibration deck KamLAND Full-Volume Calibration 4π calibration system inside Karsten view Heeger, of Univ. KamLAND of Wisconsin detector La Thuile, March 3, 2009

11 Full-Volume Calibration Design Concept glovebox with motion spools control cables calibration source calibration pole Z [m] Calibration Data 8 6 Z [m] X [m] X [m] 60Co sources along pole the level of detected activity. The source activity traces the outline of the calibration of the system location. The outer dotted line represents the balloon boundary. The inner lots like these were used during the deployment to confirm the location of the system The progression from left to right illustrates the sequence in which the pole was swept he detector. 60Co/ 68 Ge source at end ing the stability of this temperature gradient is critical to of the Wisconsin success of the low-background La Thuile, phase pu- March 3, 2009 Karsten Heeger, Univ. rification effort.

4 2 0-2 -4-6 -6-4 -2 0 2 4 6 X [m] -6-4 -2 0 2 4 6 X [m] the level of detected

The source activity traces the outline of the calibration of the system location.

The inner lots like these were used during the deployment to confirm the location of

distribution the sequence in which of 60 the Co/ pole 68 was Ge swept he detector.

12 Full-Volume Calibration Design Concept glovebox with motion spools control cables calibration source calibration pole Z [m] Calibration Data 8 6 Z [m] X [m] X [m] the level of detected activity. The source activity traces the outline of the calibration of the system location. The outer dotted line represents the balloon boundary. The inner lots like these were used during the deployment to confirm the location of the system The progression Reconstructed from left to right vertex illustrates distribution the sequence in which of 60 the Co/ pole 68 was Ge swept he detector. composite source in 4π calibration runs. ing the stability of this temperature gradient is critical to of the Wisconsin success of the low-background La Thuile, phase pu- March 3, 2009 Karsten Heeger, Univ. rification effort.

13 KamLAND 2008: Precision Measurement of Oscillation Prompt event energy spectrum for νe number of events expected: 2179 ± 89 (syst) observed: 1609 bkgd: 276 ± 23.5 systematic uncertainties: fiducial volume reduced from 4.7% 1.8% total systematics: 4.1% (and mainly affecting θ ) is 4.1%. significance of disappearance (with 2.6 MeV threshold): 8.5σ no-osc χ 2 /ndf=63.9/17 significance of distortion: > 5σ best-fit χ 2 /ndf=21/16 (18% C.L.) Detector-related (%) Reactor-related (%) m 2 21 Energy scale 1.9 ν e -spectra [7] 0.6 Event rate Fiducial volume 1.8 ν e -spectra 2.4 Energy threshold 1.5 Reactor power 2.1 Efficiency 0.6 Fuel composition 1.0 Cross section 0.2 Long-lived nuclei 0.3

14 KamLAND 2008: Precision Measurement of Oscillation L/E Dependence Data - BG - Geo & e Expectation based on osci. parameters determined by KamLAND Phys.Rev.Lett.100:221803, L0=180km L 0 /E &e (km/mev) L/E figure demonstrates ν oscillation SNO observes neutrino flavor change, finds evidence for neutrino mass KamLAND demonstrates ν oscillation, precision measurement of Δm 2

15 6! 5! 4! 1 2! 3!! KamLAND 2008: Oscillation Parameters Rate-Shape-Time Analysis 2 $# ! 3! 2! 1! ) 2 (ev KamLAND 95% C.L. 99% C.L % C.L. best fit $m 2 21 Solar 95% C.L. 99% C.L % C.L. best fit tan " 12 $# KamLAND+solar (combined under assumption of CPT invariance) KamLAND makes precise determination of Δm12 2 (~2.8%) Δm =7.59 x10-5 ev tan 2 Θ=

16 KamLAND and Solar Neutrino Fits KamLAND and solar best fit values are not quite the same. solar ν versus reactor ν CPT-violation? Other new physics? sin 2 2θ13 0? Balantekin & Yilmaz, J. Phys. G 35, (2008) (arxiv: [hep-ph] ).

17 Understanding the Mixing Angles Neutrino Mixing Matrix U e1 U e2 U e U e 3 U = U µ1 U µ2 U µ 3 = U τ1 U τ 2 U τ U MNSP Matrix Maki, Nakagawa, Sakata, Pontecorvo current best limit sin 2 2θ13 < CL arxive: cosθ 13 0 e iδ CP sinθ 13 cosθ 12 sinθ = 0 cosθ 23 sinθ sinθ 12 cosθ sinθ 23 cosθ 23 e iδ CP sinθ 13 0 cosθ 0 e iα / 2 0 iα / 2+iβ e atmospheric, K2K reactor and accelerator SNO, solar SK, KamLAND 0νββ θ 23 = ~ 45 θ 13 =? maximal? θ 12 ~ 32 large, but not maximal!

Precision Measurement of θ 13 with Reactor Antineutrinos Search for θ 13 in new oscillation experiment with multiple detectors Δm 2 P ee 1 sin 2 2θ 13 sin 2 31 L Δm cos 4 θ 13 sin 2 2θ 12 sin 2 21 4E

18 Precision Measurement of θ 13 with Reactor Antineutrinos Search for θ 13 in new oscillation experiment with multiple detectors Δm 2 P ee 1 sin 2 2θ 13 sin 2 31 L Δm cos 4 θ 13 sin 2 2θ 12 sin E ν 4E ν 2 L Small-amplitude oscillation due to θ 13 integrated over E 1.1 Large-amplitude oscillation due to θ θ 13 ~1-1.8 km > 0.1 km νe N osc /N no_osc Δm 2 13 Δm 2 23 detector 1 detector Baseline (km)

19 Concept of Reactor θ13 Experiments Measure ratio of interaction rates in multiple detectors νe near distance L ~ 1.5 km far Measured Ratio of Rates Detector Mass Ratio, H/C Detector Efficiency Ratio sin 2 2θ 13

World of Proposed Reactor θ13 Neutrino Experiments Diablo Canyon, USA Braidwood, USA Chooz, France Krasnoyasrk, Russia Kashiwazaki, Japan RENO, Korea Daya Bay, China Angra, Brazil Daya Bay,

20 World of Proposed Reactor θ13 Neutrino Experiments Diablo Canyon, USA Braidwood, USA Chooz, France Krasnoyasrk, Russia Kashiwazaki, Japan RENO, Korea Daya Bay, China Angra, Brazil Daya Bay, Double Chooz, and Reno - international collaborations - started construction Angra - R&D - nuclear proliferation studies Daya Bay - most precise experiment - only experiment to reach sin 2 2θ13 < 0.01

21 Daya Bay, China water pool RPCs antineutrino detectors ~ 900 ν events/ detector/day

e + p e + + n Gd-doped liquid scintillator steel tank acrylic tanks photomultipliers

22 Daya Bay Antineutrino Detectors 8 identical, 3-zone detectors no position reconstruction, no fiducial cut calibration system liquid scintillator mineral oil ν e + p e + + n Gd-doped liquid scintillator steel tank acrylic tanks photomultipliers target mass: 20t per detector detector mass: ~ 110t photosensors: 192 PMTs energy resolution: 12%/ E

23 Daya Bay Antineutrino Detector Construction detector tank calibration system photomultipliers acrylic target vessels

24 Antineutrino Event Rates and Signal Daya Bay near site 840 Ling Ao near site 760 Far site 90 ν e + p e + + n 0.3 b events/day per 20 ton module + p D + γ (2.2 MeV) (delayed) 49,000 b Prompt Energy Signal + Gd Gd* Gd + γʼs (8 MeV) (delayed) Delayed Energy Signal 1 MeV 8 MeV 6 MeV 10 MeV

25 Systematic Uncertainties Detector-Related Uncertainties Absolute measurement Relative measurement O( %) precision for relative measurement between detectors at near and far sites Ref: Daya Bay TDR

26 Construction Progress and Schedule entrance portal tunneling surface assembly building March 2009: Assembly building occupancy Summer 2009: Near Hall occupancy Summer 2010: Near Hall ready for data Summer 2011: Far Hall ready for data

27 Expected Precision and Sensitivity of Daya Bay Expected Precision to νe Flux past reactor experiments = 1 detector past Daya Bay - projected uncertainty next generation of experiments > 2 detectors KamLAND Daya Bay Sensitivity to sin 2 2θ13 sin 2 2θ13 < 90% CL in 3 years of data taking

28 Search for θ13: A Possible Scenario Sin 2 2θ 13 (90%CL) 10-1 MINOS OPERA Chooz Excluded Fig: M. Mezzetto World limit Double Chooz first hint of θ13 by Double Chooz possible if θ13 large T2K precision measurement at 1% level by Daya Bay % CL sensitivity Computed with: δ CP =0 sign( m 2 )=+1 Daya Bay early measurement of θ13 will help make decision on future long-baseline experiments Year precision measurement of θ13 for unambiguous discovery and combined analysis with T2K and NOvA

29 Summary and Conclusions Non-accelerator experiments were key in discovering neutrino mass and oscillations in the past decade ( ). Reactor experiments have made and will make significant contributions: KamLAND discovered reactor νe oscillation and has made precise measurement of Δm 2 12 Daya Bay reactor experiment will be able to provide the most accurate measurement of sin 2 2θ13 in the next few years. Day Bay is funded, civil and detector construction are progressing. Data taking at near site will begin in Reactor θ13 experiments will help determine the future of neutrino oscillation physics (long-baseline, CP) and provide input to analysis of accelerator experiments.

KamLAND Collaboration Text RCNS, Tohoku University University of Alabama UC Berkeley/LBNL California Institute of Technology Colorado State University Drexel University University

30 KamLAND Collaboration Text RCNS, Tohoku University University of Alabama UC Berkeley/LBNL California Institute of Technology Colorado State University Drexel University University of Hawaii Kansas State University Louisiana State University Stanford University University of Tennessee UNC/NCSU/TUNL IN2P3-CNRS and University of Bordeaux University of Wisconsin

Daya Bay Collaboration Europe (3) (9) JINR, Dubna, Russia Kurchatov Institute, Russia Charles University, Czech Republic North America (14)(73) BNL, Caltech, George Mason Univ., LBNL, Iowa state Univ.

31 Daya Bay Collaboration Europe (3) (9) JINR, Dubna, Russia Kurchatov Institute, Russia Charles University, Czech Republic North America (14)(73) BNL, Caltech, George Mason Univ., LBNL, Iowa state Univ. Illinois Inst. Tech., Princeton, RPI, UC-Berkeley, UCLA, Univ. of Houston, Univ. of Wisconsin, Virginia Tech., Univ. of Illinois-Urbana-Champaign ~ 210 collaborators Asia (18) (125) IHEP, Beijing Normal Univ., Chengdu Univ. of Sci. and Tech., CGNPG, CIAE, Dongguan Polytech. Univ., Nanjing Univ.,Nankai Univ., Shandong Univ., Shenzhen Univ., Tsinghua Univ., USTC, Zhongshan Univ., Hong Kong Univ., Chinese Hong Kong Univ., National Taiwan Univ., National Chiao Tung Univ., National United Univ.

Reactor Neutrino Oscillation Experiments: Status and Prospects

6! 5! 4! 1 2! 3!! Reactor Neutrino Oscillation Experiments: Status and Prospects Survival Probability 1 0.8 0.6 0.4 0.2 0 20 4! 15 Karsten M. Heeger University of Wisconsin Data - BG - Geo & e 99.73% C.L.