Recent Discoveries in Neutrino Oscillation Physics & Prospects for the Future

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1 Recent Discoveries in Neutrino Oscillation Physics & Prospects for the Future Karsten M. Heeger Lawrence Berkeley National Laboratory SNO φ ES SNO φ CC SNO φ NC SSM φ NC φe (10 6 cm-2 s-2)

Reactor (KamLAND) Neutrinos are not massless Evidence for neutrino

2 Recent Discoveries in Neutrino Oscillation Physics 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

Early Indications Solar Neutrino Flux Measurements 4p + 2e 4He + 2ν e + 26.

3 Early Indications Solar Neutrino Flux Measurements 4p + 2e 4He + 2ν e MeV (pp chain) 1960 s Ray Davis Chlorine detector First Solar Model calculations For 30 years CC and ES measurements of solar ν e (CC) 37 Cl + ν e 37 Ar + e - 71 Ga + ν e 71 Ge + e - (ES) ν x + e - ν x + e - Data are incompatible with standard and non-standard solar models

4 What is the Solution? Are experiments in error? But all experiments show similar effect. Is astrophysics wrong? Perhaps, but even with solar ν fluxes (Φ pp, Φ 7Be, Φ 8B ) as free parameters, cannot reproduce the data. Data are incompatible with standard and non-standard solar models! KMH, PRL 77:3270 (1996) New neutrino physics such as oscillations? Cl-Ar and Ga detectors are only sensitive to ν e. Flux would appear low.

Experimental Studies Sun Solar core ~10 8 kilometers Earth Underground νe detector Natural Sources Man-Made Sources The Sun Atmospheric Neutrinos Accelerators K2K Opera Nuclear Reactors 37 Cl

5 Experimental Studies Sun Solar core ~10 8 kilometers Earth Underground νe detector Natural Sources Man-Made Sources The Sun Atmospheric Neutrinos Accelerators K2K Opera Nuclear Reactors 37 Cl Kamiokande GALLEX SuperKamiokande SAGE SNO IMB Soudan MACRO Kamiokande SuperKamiokande Chorus (LSND) Primary neutrino source p + p D + e+ + νe p ~30 kilometers target horn νe e+ µ + ν µ ν µ Underground νe, νe, ν µ, ν µ detector π + π+ decay pipe π + µ + π0 Cosmic-ray shower Atmospheric neutrino source π + µ + + νµ e+ + νe + ν µ π µ + ν µ e + νe + ν µ absorber detector Bugey ILL Palo Verde Goesgen Chooz KamLAND

6 Neutrino Observations with Super-K Atmospheric Neutrino Studies π+ π 0 Cosmic-ray shower ~30 kilometers µ + νe e+ ν µ ν µ Atmospheric neutrino source Underground νe, νe, ν µ, ν µ detector π + µ + + ν µ π e+ + νe + ν µ µ + νµ e + νe + ν µ

7 Super-Kamiokande Atmospheric Neutrino Studies ν µ ν τ 2-flavor osc.

8 KEK to Kamioka (K2K) Experiment Accelerator-based long baseline neutrino oscillation experiment to test atmospheric oscillations atm K2K L km 250 km E ν 0.1~100 GeV ~ 1.3 GeV Δm ~10-4 ev 2 > 2x10-3 ev 2 ν e /ν µ 50% ~1% data from expected: 80.1 events observed: 56 events

9 Super-Kamiokande L/E Analysis Searching for Direct Evidence of Oscillations Neutrino oscillation Neutrino decay Neutrino decoherence

10 Super-Kamiokande Solar Neutrino Detection ν e + e ν e + e Seasonal Variation Elastic Scattering Observed/SSM = ± ± 0.015

11 Sudbury Neutrino Observatory 2092 m to Surface (6010 m w.e.) PMT Support Structure, 17.8 m cm PMTs ~55% coverage within 7 m Acrylic Vessel, 12 m diameter 1000 Tonnes D 2 O Need solar model-independent measurement Tonnes H 2 O, Outer Shield Urylon Liner and Radon Seal Need experiment that measures ν e and ν µ,τ separately.

12 Neutrino Detection in SNO Neutrino Interactions on Deuterium and their Flavor Sensitivity Charged-Current (CC) ν e +d e - +p+p E thresh = 1.4 MeV Measurement of energy spectrum Neutral-Current (NC) ν x +d ν x +n+p E thresh = 2.2 MeV Measures total 8 B flux from Sun Elastic Scattering (ES) ν x +e - ν x +e - Strong directional sensitivity

13 SNO - Enhanced Neutron Detection with NaCl Higher capture cross section Higher energy release Many gammas n 36 Cl * 35 Cl 36 Cl γ σ = b σ = 44 b 35 Cl+n 8.6 MeV 2 H+n 6.0 MeV 3 H 36 Cl

14 Solar Neutrino Physics with SNO What can we learn from measuring the NC interaction rate (total active 8 B solar neutrino flux) at SNO? Total 8 B ν flux (NC) versus ν e flux (CC) [CC] [NC] = [ν e ] [ν e + ν µ +ν τ ] Test of neutrino flavor change Total flux of solar 8 B neutrinos Diurnal time dependence Test of solar models Test of neutrino oscillations Distortions of neutrino energy spectrum Test of neutrino oscillations

15 SNO Signal Extraction Isotropy Data from July 26, 2001 to Oct. 10, live days Blind analysis performed 3055 candidate events: CC NC ES Kinetic Energy Angle to Sun

16 Solving the Solar Neutrino Problem: Test of Neutrino Flavor Change SNO Flux Results 8 B from CC SNO +ES SK (2001) ES SNO (2001) CC SNO (2001) NC SNO (2002) ES SNO (2002) CC SNO (2002) Neutrino Signal (SSM/BP00) Neutral Current (NC) CC Neutral-Current shape Elastic Scattering Charged-Current constrained CC shape unconstrained ν e + ν µ +ν τ Elastic Scattering (ES) SSM ν e (ν µ +ν τ ) Charged Current (CC) ν e 2/3 of initial solar ν e are observed at SNO to be ν µ,τ Standard Solar Model predictions for total 8 B flux in excellent agreement!

17 Flavor Content of 8 B Solar Neutrino Flux 8 B Standard Solar Model (SSM01) 5.05 x 10 6 cm -2 s -1 NC Salt Constrained 4.90 ± 0.38 x 10 6 cm -2 s -1 NC Salt Unconstrained 5.21 ± 0.47 x 10 6 cm -2 s -1 CC/NC Ratio ± (stat) ± (sys)

18 Solar Neutrino Measurements Measured Rates Closed circles: experimental data Energy-dependent effect? Ref: hep-ph/

19 Neutrino Oscillations in the Sun (MSW Effect) Flavor conversion can be a resonant effect in matter Mikeheyev - Smirnov - Wolfenstein Effect

20 Neutrino Oscillations in the Sun (MSW Effect) 8 B ν 7 Be ν pp ν sin 2 2θ=

21 Oscillation Interpretation of Solar Neutrino Data 10-3 cosθ 12 sinθ 12 0 sinθ 12 cosθ SMA LMA solar ν Matter-enhanced oscillations (MSW): Energy-dependent oscillation effect Δm 2 (ev 2 ) LOW Gallium GALLEX/GNO, SAGE Chlorine Homestake Water Super-Kamiokande 10-8 SAGE&GALLEX & GALLEX Kamiokande Homestake 10-9 sin 2 2θ

22 2-ν Oscillation Region SNO gives m 1 -m 2 hierarchy (Chooz also required) m 2 >m 1 m 1 >m 2 Global fit selects Large Mixing Angle (LMA) Solution

23 Solar Neutrino Measurements Best Global Fits / Measured Rates Open circles: combined best oscillation fit Closed circles: experimental data Ref: hep-ph/

24 Oscillation Parameters and Reactor Experiments Reactor and Beamstop Neutrinos ν µ ν s ν e Atmospheric and Reactor Neutrinos ν µ ν τ Solar and Reactor Neutrinos? ν e ν µ,τ Large mixing favored LMA solution can be tested with reactor neutrinos Status: Summer 2002 Murayama

Search for Neutrino Oscillations with Reactor Neutrinos 50 Years of Reactor Neutrino Physics 1953 First reactor neutrino experiment 1956 Detection of Free Antineutrino, F.

25 Search for Neutrino Oscillations with Reactor Neutrinos 50 Years of Reactor Neutrino Physics 1953 First reactor neutrino experiment 1956 Detection of Free Antineutrino, F. Reines and C.L. Cowan Nobel Prize in 1995 No signature of neutrino oscillations until 2002! Results from solar experiments suggest study of reactor neutrinos with a baseline of ~ 180 km Japan

26 KamLAND Underground Laboratory

27 Reactor Antineutrinos Spectrum from Principal Reactor Isotopes From Japanese Reactors Kashiwazaki Takahama Ohi ~ 200 MeV per fission ~ 6 ν e per fission ~ 2 x ν e /GW th -sec

capture, ~ 190 µs capture time (a) Flux at detector (b) ν cross-section (c) Interactions in detector (c)

28 KamLAND - Kamioka Liquid Scintillator Antineutrino Detector Uses reactor neutrinos to study ν oscillation with a baseline of L ~ km Coincidence Signal: ν e + p e + + n Prompt e + annihilation Delayed n capture, ~ 190 µs capture time (a) Flux at detector (b) ν cross-section (c) Interactions in detector (c) (b) Ty (a) Energy (MeV) KamLAND studies the disappearance of ν e and measures interaction rate energy spectrum

29 Event Selection Delayed Energy Window Muon veto from 12 C(n,γ) t cap = 188 +/- 23 msec Vertex and Time Correlation R < 5 m 0.5 < dt < 660 msec dr < 1.6 m dz > 1.2 m

First Direct Evidence for Reactor ν e Disappearance Reactor Neutrino Physics 1956-2003 PRL

8 ± 5.6 events Background 1 ± 1 events accidental 0.0086 ± 0.0005 9 Li/ 8 He 0.94 ± 0.

30 First Direct Evidence for Reactor ν e Disappearance Reactor Neutrino Physics PRL 90:021802, 2003 Observed 54 events syst err. 6.4% 162 ton yr, E prompt > 2.6 MeV Expected 86.8 ± 5.6 events Background 1 ± 1 events accidental ± Li/ 8 He 0.94 ± 0.85 fast neutron < 0.5 KamLAND provides evidence for neutrino oscillations together with solar experiments.

31 Is the KamLAND Neutrino Spectrum Distorted? 2-ν oscillation: best-fit No oscillation, flux suppression χ 2 / 8 d.o.f = 0.31 Data and best oscillation fit consistent at 93% C.L. Data and best oscillation fit consistent at 53% C.L. as determined by Monte Carlo

32 Oscillation Parameters Before and After KamLAND Before KamLAND After KamLAND Region favored by solar ν experiments

33 Determination of Oscillation Parameters Δm 122, θ 12 Before SNO-Salt With SNO-Salt Assume CPT Δm ν 2 - Δm ν 2 < 1.3 x 10-3 ev 2 at 90% CL LMA I only at > 99% CL Maximal mixing ruled out (5.4σ) Possible Sterile Admixture? KamLAND + SNO-Salt sin 2 η sterile < 0.09

34 What we have learned ν transform flavor Atmospheric ν data explained extremely well by oscillations - primarily ν µ ν τ conversion - mixing angle θ 23 is very large, possibly maximal - Δm 2 ~ 2 x 10-3 ev 2 Solar ν e change primarily to other active ν s - if oscillations, mixing angle θ 12 is large but not maximal and Δm 12 ~ 7 x 10-5 ev 2 (LMA solution) - matter predicted to play a role in transformation - other modes for solar neutrino flavor transformation (sterile, RSFP, CPT ) can play only a subdominant role. convincingly show that the flavor transitions of solar neutrinos are affected by Mikheyev- Smirnov-Wolfenstein (MSW) effects G.L. Fogli et. al, hep-ph/

35 Cosmological Implications Experimental Results Atmospheric neutrinos: Δ m ev 2 one neutrino mass > 0.04 ev SNO + KamLAND: Δ m x 10-5 ev 2 one neutrino mass > ev Limits on ν e mass give: m(ν 1,2,3 ) < 2.2 ev Implications Σ of neutrino masses: Laboratory limit on ν fraction of universe closure density: Large-scale structure limit : < m 1 +m 2 +m 3 < 6.6 ev < Ω ν < < Ω ν < 0.02

36 Neutrinos in the Universe 1 Ω Cosmological Density 1.0 ± 0.1 Matter & Energy Dark Energy 0.7 ± 0.1 Matter 0.3 ± 0.1 Matter Composition? Cold Dark Matter 0.35 ± 0.1 Observed Particle Dark Matter 0.1? Non-Baryonic Dark Matter < 0.15 Baryons ± < ? Dark Baryons Neutrinos Stars ~0.003 >

37 Constraining the Mass of Fermions: New Limits on Neutrino Masses from Oscillation Experiments Fermion Masses Mass Differences PDG 2000 Δm 2 solar = 5.0 x 10-5 ev 2 Δm 2 atm = 3.2 x 10-3 ev 2 m ν1 <m ν2 from solar exp. ν e ν µ ν τ Tritium beta-decay m ν < 2.2 ev (95 % CL) PDG SNO + SK (ν 3 ) < ν 1 < ν 2 < (ν 3 ) 0.05 < Σm 1,2,3 < 6.6 ev Adapted from Murayama

38 What s next for KamLAND? Continued Running Enlarge Fiducial Volume Improve Calibration Search for Spectral Distortions Improve Δm 2 and θ 12 Search for geo-, supernova, and relic-supernova anti-neutrinos. Nucleon decay studies.

39 Defining θ 12 and Δm 12 2 with SNO and KamLAND Is it all consistent? Day/Night variation, Spectrum from MSW Solar versus Reactor Oscillation de Holanda et al., hep-ph/ , Barger et al., hep-ph/

7 Be Solar Neutrinos at KamLAND A Background Challenge Direct detection of solar 7 Be neutrinos through elastic scattering Singles signal 91% 7% 0.

40 7 Be Solar Neutrinos at KamLAND A Background Challenge Direct detection of solar 7 Be neutrinos through elastic scattering Singles signal 91% 7% 0.2% 0.008% 7 Be ν e measurement can improve solar models. Unlikely to improve on θ 12. Checks oscillation prediction of 7 Be ν e flux. Ref: KamLAND proposal

41 7 Be Solar Neutrinos at KamLAND A Background Challenge Backgrounds in the 7 Be signal region currently about 10 6 times too high Working on purification methods to remove 85 Kr (from nitrogen used in purification) 210 Pb, 210 Pb (from decay of radon that got into the system)

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

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

44 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

45 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 maximal tan 2 θ 13 < 0.03 at 90% CL small at best θ 12 ~ 32 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

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

46 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

47 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 4E ν 4E ν 2 L p target cos 4 θ 13 sin 2 2θ 13 horn 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

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

49 Search for Subdominant Oscillation Effects sin 2 (2θ 13 ) P(ν e ν e ) Dominant θ 12 Oscillation 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 4E ν 4E ν 2 L cos 4 θ 13 sin 2 2θ 12

50 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/

51 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 independent of of absolute reactor

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

53 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

Precision Reactor Measurement of θ 13 Deep Horizontal-Access Experiment 1-2 km nuclear reactor sin 2 2θ 13 scintillator ν detectors, 50-100 t study relative rate

54 Precision Reactor Measurement of θ 13 Deep Horizontal-Access Experiment 1-2 km nuclear reactor sin 2 2θ 13 scintillator ν detectors, t study relative rate difference and spectral distortions projected sensitivity: sin 2 2θ Overburden: Possible Sites: Near mwe Far >700 mwe Diablo Canyon, CA Daya Bay, China

55 Classes of θ 13 Experiments & Sensitivity small medium large - existing underground facility -deep -optimized baseline and detector size

56 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

57 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

58 sin 2 2θ 13 Sensitivity Limits.10 years from now Ref: Huber et al., hep-ph/

59 Reactor & Accelerator Experiments Ref: McKeown

Outlook and Milestones Search for sterile ν, test of LSND (2005?) Measurement of θ 13 (2009?

01 (for a large true θ 13 ) can provide significant new constraints when combined with 5yr superbeam

1956 First observation of neutrinos 1980s & 1990s Reactor ν measurements in U.S.

60 Outlook and Milestones Search for sterile ν, test of LSND (2005?) Measurement of θ 13 (2009?) Reactor measurements with sin 2 2θ 13 ~ 0.01 (for a large true θ 13 ) can provide significant new constraints when combined with 5yr superbeam result perhaps even decide hierarchy and yield information on δ CP First observation of neutrinos 1980s & 1990s Reactor ν measurements in U.S. and Europe 2002 Evidence for ν disappearance Other important ν questions remain: mass, CP, 0νββ 2004 and beyond Search for θ 13 Superbeam Experiments Will significantly increase precision, show correlations between sin 2 2θ 13 and δ CP

- Future Prospects in Oscillation Physics -

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 Evidence