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1 Measuring θ 13 and the Search for Leptonic CP Violation - Future Prospects in Oscillation Physics - Karsten M. Heeger Lawrence Berkeley National Laboratory ν e flux θ 13 =? P ee, (4 MeV) 1/r 2

(KamLAND) Neutrinos are not massless Evidence for neutrino

2 Evidence for Mixing of Massive Neutrinos ν µ ν τ Atmospheric (Super-K) Accelerator (K2K) ν e ν µ,τ Solar (SNO) Reactor (KamLAND) Neutrinos are not massless Evidence for neutrino flavor conversion ν e ν µ ν τ Experimental results show that neutrinos oscillate

3 Open Questions in Neutrino Physics Is U 13 = 0? Is there CP violation for neutrinos? What are the values of Δm 2, U ij? Future reactor and accelerator experiments Is U 3-dimensional? 4? 6?? or, is the 3-D version unitary? or, are there sterile ν? MiniBoone What are the absolute masses? What is the level ordering of 2,3 (or 1,3)? Are ν s Dirac or Majorana particles? Direct mass measurements and 0νββ

4 Neutrino Mixing Angles and Leptonic Unitarity Triangle Ue2 Uµ2* S = 2J Ue1 Uµ1* Karsten Heeger, LBNL CWRU - April 29, 2004 Ue3Uµ3*

5 U MNSP, θ 13, and CP U MNSP Neutrino Mixing Matrix U e1 U e2 U e 3 U = U µ1 U µ2 U µ 3 Dirac phase Majorana phases U τ1 U τ 2 U τ 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 tan 2 θ 13 < 0.03 at 90% CL θ 12 ~ 32 1σ sin θ Ref: Smirnov

6 U MNSP, θ 13, and CP U MNSP Neutrino Mixing Matrix U e1 U e2 U e 3 U = U µ1 U µ2 U µ 3 Dirac phase Majorana phases U τ1 U τ 2 U τ 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 tan 2 θ 13 < 0.03 at 90% CL θ 12 ~ 32 maximal small at best large No good ad hoc model to predict θ 13. If θ 13 < 10-3 θ 12, perhaps a symmetry? θ 13 yet to be measured determines accessibility to CP phase

7 Unknown Oscillation Parameters sin 2 (2θ 13 ) sign of Δm 13 2 δ CP

8 Three Questions I) What is size of sin 2 (2θ 13 )? Δm 23 2 from SK II) What is the mass hierarchy? Sign of Δm 13 2 hep-ph/ Δm 2 Δm atm 2 III) Is there CP violation? Measure δ. Amount of CP violation is given by J lepton ~ cos 2 (θ 13 )sin(2θ 12 )sin(2θ 23 )sin(2θ 13 )sin(δ CP ) ~1 ~ 0.9 ~1

Oscillation Measurements Probe Fundamental Physics Physics at high mass scales, physics of flavor, and unification: Why are the mixing angles large, maximal, and small?

9 Oscillation Measurements Probe Fundamental Physics Physics at high mass scales, physics of flavor, and unification: Why are the mixing angles large, maximal, and small? Is there CP violation, T violation, or CPT violation in the lepton sector? Is there a connection between the lepton and the baryon sector? U MNSP = V CKM = big big small? big small tiny big big big? small big tiny big big big tiny tiny big θ 13 Leptogenesis and the role of neutrinos in the early Universe The Mystery of the Matter-Antimatter Asymmetry

10 S. Glashow L. Wofenstein

11 Mass Spectrum and Mixing U e3 2 ν 3? ν 2 ν 1 Δm 2 sun mass ν 2 ν 1 Δm 2 atm Δm 2 sun mass U e3 2 ν 3 Δm 2 atm Normal mass hierarchy (ordering) Inverted mass hierarchy (ordering) Type of mass spectrum: Normal, Inverted, Degenerate Absolute mass scale U e3 =?

Desired Experimental Sensitivity to θ 13? if sin 2 2θ 13 < 0.01 smaller values of θ 13 harder to understand. For MSSM shift of Δsin 2 2θ 13 > 0.01 is plausible.

12 Desired Experimental Sensitivity to θ 13? if sin 2 2θ 13 < 0.01 smaller values of θ 13 harder to understand. For MSSM shift of Δsin 2 2θ 13 > 0.01 is plausible. Can bound model parameters if experiment sets limit in the range of sin 2 2θ 13 < Precision of the order of quantum corrections to neutrino masses and mixings interesting. Small θ 13 : numerical coincidence or underlying symmetry? sin 2 2θ 13 < 0.01 is interesting sensitivity

13 Measuring θ 13 Method 1: Accelerator Experiments P µe sin 2 2θ 13 sin 2 2θ 23 sin 2 Δm 31 2 L 4 E ν +... appearance experiment ν µ ν e measurement of ν µ ν e and ν µ ν e yields θ 13,δ CP baseline O( km), matter effects present Method 2: Reactor Neutrino Oscillation Experiment Δm 2 P ee 1 sin 2 2θ 13 sin 2 31 L + Δm 21 4 E ν 4E ν 2 L p target horn cos 4 θ 13 sin 2 2θ 13 π + decay pipe π + µ + absorber ν e detector ν e ν e disappearance experiment ν e ν x look for rate deviations from 1/r 2 and spectral distortions observation of oscillation signature with 2 or multiple detectors baseline O(1 km), no matter effects

14 ν e Appearance Experiments For example, T2K- From Tokai To Kamioka mass hierarchy CP violation matter

15 Tokai to Kamioka (T2K)

16 Concept of the Off-Axis Beam By going off axis, beam energy is reduced and spectrum becomes very sharp at 730 km Allows experiment to pick an energy for the maximum oscillation signal Removes the high-energy flux that contributes to background "Not magic but relativistic kinematics" At Fermilab - Allows experiment to use the NuMI beam for several experiments simultaneously - Minos ν µ disappearance on-axis - Off axis ν µ ν e search "Off-axis"

17 Search for sin 2 (2θ 13 ) & Subdominant Oscillation Effects Dominant θ 12 Oscillation P(ν e ν e ) P ee 1 cos 4 θ 13 1 sin 2 θ 12 sin 2 Δm 12 2 L 4E ν Distance (m) Subdominant θ 13 Oscillation Δm 2 P ee 1 sin 2 2θ 13 sin 2 31 L + Δm 21 4 E ν 4E ν 2 L cos 4 θ 13 sin 2 2θ 12

18 Current Knowledge of θ 13 from Reactors Reactor anti-neutrino measurement at 1 km at Chooz + Palo Verde: ν e ν x M. Appollonio, hep-ex/

19 Global Constraints on θ 13 Maltoni et al., hep-ph/ Chooz Δm 23 2 from SK With added SNO CC/NC + KamLAND Constraint 90, 95, 99% CL Solar data provide constraints at low Δm 2 atm sin 2 (2θ 13 ) = 0.02 (global best fit)

20 Chooz, France Reactor on: 2991 Reactor off: 287 candidate ν e events. (9.5% backgrounds!) Chooz was unique! Determined backgrounds during reactor-off period reactor-off data to determine backgrounds Ref: hep-ex/

Overburden Requirements for Reactor Experiments Chooz candidate ν e events 2991 287 Ref: hep-ex/0301017 Chooz subtracted 9.5% of backgrounds, presumably - fast neutrons, and - spallation backgrounds.

21 Overburden Requirements for Reactor Experiments Chooz candidate ν e events Ref: hep-ex/ Chooz subtracted 9.5% of backgrounds, presumably - fast neutrons, and - spallation backgrounds. Minimum Overburden Scaling Chooz background with muon spectrum that generates spallation backgrounds: bkgd bkgd depth depth (mwe) (mwe) 10% 10% < 5% 5% > < 2% 2% > < 1% 1% >

22 Chooz Systematics theor. kinetic energy spectrum 2.1% detector response 1.7% total 2.7% Ref: Apollonio et al., hep-ex/ neutron capture: lowest efficiency, largest relative error Absolute measurements are difficult!

23 KamLAND - Systematic Uncertainties E > 2.6 MeV % Total liquid scintillator mass 2.1 Fiducial mass ratio 4.1 Energy threshold 2.1 Tagging efficiency 2.1 Live time 0.07 FV volume calibration energy calibration or analysis w/out threshold detection efficiency Reactor power 2.0 Fuel composition 1.0 ν e spectra 2.5 cross section 0.2 given by reactor company, difficult to improve on theoretical, model-dependent Total uncertainty 6.4 %

24 Reactor Neutrino Measurement of θ 13 - Basic Idea ν e flux θ 13 =? P ee, (4 MeV) 1/r 2 Δm 2 P ee 1 sin 2 2θ 13 sin 2 31 L + Δm 21 4 E ν 4E ν atmospheric frequency dominant 2 L cos 4 θ 13 sin 2 2θ 12 last term negligible for Δm 2 31 L ~ π /2 and sin 2 2θ E ν

Reactor Neutrino Measurement of θ 13 Present Reactor Experiments single detector Future θ 13 Reactor Experiment detector 1 detector 2 Absolute Flux and Spectrum (a) Flux at detector (b) ν

25 Reactor Neutrino Measurement of θ 13 Present Reactor Experiments single detector Future θ 13 Reactor Experiment detector 1 detector 2 Absolute Flux and Spectrum (a) Flux at detector (b) ν cross-section (c) ν spectrum in detector Ratio of Spectra independent (c) of of absolute reactor reactor ν flux flux largely largely eliminate cross-section errors errors relative detector calibration rate rate and and shape shape information (a) relative detector (b) calibration Energy (MeV) Energy (MeV)

26 Measuring θ 13 with Reactor Neutrinos Novel Oscillation Experiment with Multiple Detectors detector 1 detector 2 Δm 2 P ee 1 sin 2 2θ 13 sin 2 31 L + Δm 21 4E ν 4E ν 2 L cos 4 θ 13 sin 2 2θ 12 Diablo Canyon relative ν flux measurement between 2 detectors eliminates most systematic errors 1-2 km nuclear reactor projected sensitivity: sin 2 2θ Ref: theta13.lbl.gov, hep-ex/ underground scintillator ν detectors, t study relative rate difference and spectral distortions

27 Detector Baseline and sin 2 2θ 13 Sensitivity Δm 2 P ee 1 sin 2 2θ 13 sin 2 31 L + Δm 21 4 E ν 4 E ν 2 L cos 4 θ 13 sin 2 2θ Ratio (0.01,3.0E-3) Ratio (0.01,2.5E-3) Ratio (0.01,2.0E-3) Ratio (0.01,1.5E-3) Ratio (0.01,1.0E-3) 80% of expected oscillation effect N ib osc /Nib no osc N osc /N no-osc Ideal baseline ~1.5-2 km Distance (m) Would like to choose and optimize baseline as Δm 2 23 becomes better known

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

existing infrastructure Detector locations determined by infrastructure

29 Reactor θ 13 Experiment at Krasnoyarsk First Idea to Measure θ 13 at Reactors at Neutrino2000 Unique Feature - underground reactor - existing infrastructure Detector locations determined by infrastructure ~1.5 x 10 6 ev/year ~20000 ev/year Reactor Ref: Marteyamov et al, hep-ex/

30 Kashiwazaki, Japan - 7 nuclear power stations, World s most powerful reactors - requires construction of underground shaft for detectors far near near 70 m 70 m m Kashiwazaki-Kariwa Nuclear Power Station 6 m shaft hole, m depth

31 Improving Chooz Double-Chooz Project 10 tons detectors 8.4 GW th reactor power 300 mwe overburden at far site 50 mwe overburden at near site km 1.05 km Double-Chooz Sensitivity sin 2 (2θ 13 ) < 0.03 at 90% CL after 3 yrs, Δm atm 2 = 2 x 10-3 ev 2

01 1-2 km nuclear reactor sin 2 2θ 13 scintillator ν detectors, 50-100 t study relative rate

32 Precision Measurement of θ 13 with Reactor Neutrinos Deep Horizontal-Access Experiment to reach sin 2 2θ 13 < km nuclear reactor sin 2 2θ 13 scintillator ν detectors, t study relative rate difference and spectral distortions projected sensitivity: sin 2 2θ days Overburden: Possible Sites: Near mwe Far >700 mwe Diablo Canyon, CA Daya Bay, China

33 Tunnel design Adjustable Baseline to maximize oscillation sensitivity to demonstrate oscillation effect

34 Tunnel design Movable Detectors allow relative efficiency calibration allow background calibration in same environment (overburden) simplify logistics (construction off-site)

35 Detector Concept acrylic vessel muon veto 5 m liquid scintillator buffer oil 1.6 m passive shield Movable Detectors allow relative efficiency calibration allow background calibration in same environment (overburden) simplify logistics (construction off-site)

36 Detector Room Concept

37 Experimental Challenges of a θ 13 Measurement at Reactors I. Backgrounds Uncorrelated Backgrounds - ambient radioactivity - accidentals Correlated Backgrounds - cosmic rays induce neutrons in the surrounding rock and buffer region of the detector - radioactive nuclei that emit delayed neutrons in the detector eg. 8 He (T 1/2 =119ms) 9 Li (T 1/2 =178ms) II. Relative Uncertainty Acceptance Energy scale and linearity III. Detector size (fiducial volume) signal statistics and muon deadtime

38 A Disappearance Measurement of θ 13 with Reactor Neutrinos Experimental Challenges Backgrounds Chooz Future Reactor Exp. Ref: hep-ph/ Ref: hep-ph/ Will we be able to measure background contributions? Backgrounds in near and far detector will be different.

39 Overburden and Muon Flux

40 Neutron Production in Rock A. da Silva PhD thesis, UCB 1996

41 Muon-Induced Production of Radioactive Isotopes in LS Isotope T 1/2 E max (MeV) Type β - 12 B 0.02 s 13.4 Uncorrelated 11 Be s 11.5 Uncorrelated 11 Li 9 Li 8 Li 8 He 0.09 s 0.18 s 0.84 s 0.12 s Correlated correlated: Correlated correlated: β-n β-n cascade, cascade, τ~few τ~few 100ms. 100ms. Uncorrelated Only Only 8 8 He, He, 9 9 Li, Li, Li Li (instable (instable isotopes). Correlated isotopes). 6 He 0.81 s 3.5 Uncorrelated β +, EC 11 C 10 C m s Uncorrelated uncorrelated: uncorrelated: single Uncorrelated single rate rate dominated dominated by by C 9 C 0.13 s 16.0 Uncorrelated 8 B 0.77 s 13.7 Uncorrelated 7 Be 53.3 d 0.48 Uncorrelated rejection through muon muon tracking and and depth depth

42 Detector and Shielding Concept Active muon tracker + passive shielding + inner liquid scintillator detector

43 Detector and Shielding Concept µ µ rock 3-layer muon tracker and active veto n passive shielding

44 Statistics and Systematics Detector Event Rate/Year ~250,000 ~60,000 ~10,000 N obs /N no-osc Statistical error: σ stat ~ 0.5% for L = 300t-yr Reactor Flux near/far ratio, choice of detector location Detector Efficiency near and far detector of same design calibrate relative detector efficiency Target Volume & no fiducial volume cut Backgrounds external active and passive shielding σ flux < 0.2% σ rel eff 1% σ target ~ 0.3% σ acc < 0.5% σ n bkgd < 1% Total Systematics σ syst ~ 1-1.5%

45 Past and Present Reactor Neutrino Experiments

46 Future Diablo Canyon Experiment

47 Goals of a Reactor Neutrino Oscillation Experiment Discovery and measurement of θ 13. Confirmation of Δm 232. Search for the effect of sterile ν. Resolving parameter degeneracy and limits on CP (from a combination with long baseline exp.) Supernova watch.

48 Classes of Reactor θ 13 Experiments & Sensitivity small medium large - existing underground facility - deep, good overburden - optimized baseline and detector size

49 Future Constraints on θ 13 Experiment sin 2 (2θ 13 ) θ 13 When? CHOOZ < 0.11 < 10 NUMI Off- Axis (5 yr) < < JPARC-nu (5 yr) < < MINOS < 0.07 < ICARUS (5 yr) < 0.04 < OPERA (5 yr < 0.06 < Angra dos Reis (Brazil) < < 5? Braidwood (US) < < 5 [2009] Chooz-II (France) < 0.03 < 5 [2009] Daya Bay (China) < < 3 [2009] Diablo Canyon (US) < < 2.9 [2009] Krasnoyarsk (Russia) < < 3.6? Kashiwazaki (Japan) < < 4.6 [2008] Upper limits correspond to 90% C.L.

50 Reactor & Long Baseline Experiments Measuring sin 2 (2θ 13 ) 3 σ Sensitivity to sin 2 (2θ 13 ) Minos Chooz 90% CL sin 2 (2θ 13 ) 0.14 NuMI Off-Axis Reactor Exp Minos 3-σ sensitivity sin 2 (2θ 13 ) = 0.07 θ 13 Reactor Exp sin 2 (2θ 13 ) < % CL NuMI Off-Axis 3-σ sens. sin 2 (2θ 13 ) < at Δm atm 2 = 2.5 x 10-3 ev 2 Ref: NuMI Off-Axis Collaboration, Progress Report 12/2003 sin 2 (2θ 13 ) reactor 90% CL= 0.01 and δ(sin 2 (2θ 13 )) = 0.006

51 sin 2 2θ 13 Sensitivity Limits.10 Years From Now Ref: Huber et al., hep-ph/

52 Oscillation Parameters 10 years from now Ref: Huber et al., hep-ph/

53 Reactor & Long Baseline Experiments Determining Mass Hierarchy sin 2 (2θ 13 ) vs P(ν e ) for P(ν e )=0.02 sin 2 (2θ 13 ) ν µ ν e appearance Ref: NuMI Off-Axis Collaboration, Progress Report 12/2003 reactor 90% CL= 0.01 and δ(sin 2 (2θ 13 )) = 0.006

54 Reactor Experiment & Noνa Ref: McKeown

55 δ CP Measurement (with / without Reactor) ν + ν JHF ν + ν JHF+NuMI ν + ν JHF+NuMI +Reactor ν + ν JHF+Reactor δ = 270 Ref: Shaevitz

56 Reactor & Long Baseline Experiments Combination of Experiments Can Detect CP Violation Accelerator ν e appearance + reactor disappearance measurement δ CP Ref: hep-ph/

57 Superbeams and Beyond - Another Approach Wide Band Beam Over Long Distance Ref: Diwan et al. PRD 68, (2003)

58 Superbeams and Beyond Ref: Diwan et al. PRD 68, (2003)

59 Motivation for Reaching sin 2 2θ 13 < 0.01 Theory and Model Building Reactor experiments can reach precision that probe quantum correction to neutrino mass and mixings. Limits on model parameters can be obtained if sin 2 2θ 13 < Input to Future Neutrino Program Reactor measurement of sin 2 2θ 13 sets the scale for pursuing mass hierarchy and CP violation. If too small (sin 2 2θ 13 < 0.01), they will be out of reach for offaxis experiments. Complementarity with Accelerator Experiments Ambiguities in off-axis experiments (sin 2 2θ 13, sin 2 2θ 23, mass hierarchy, δ). Reactor measurements help extract physics parameters. If lucky, may find indication of CP and mass hierarchy with nextgeneration experiments (precision θ 13 reactor + off-axis acc. experiment)!

µ Measurement of θ 13 with reactor neutrinos

60 Possible Future of Neutrino Oscillation Physics The Next 10 Years Accelerator neutrino studies of ν e ν µ Measurement of θ 13 with reactor neutrinos Constraining CP-violating parameters in combined analysis

Neutrino Experiments with Reactors

Neutrino Experiments with Reactors 1 Ed Blucher, Chicago Lecture 2 Reactors as antineutrino sources Antineutrino detection Reines-Cowan experiment Oscillation Experiments Solar Δm 2 (KAMLAND) Atmospheric