Status of Neutrino Science

1. Status of Neutrino Science Hitoshi Murayama LBNLnu April 11, 2003

2. Two Main Directions • Neutrino Properties • Neutrino Masses • Neutrino Mixings • Nature of Neutrinos • Neutrino as a Probe • Parton Distribution Function • Precision Electroweak Physics • Neutrino Astrophysics LBNLnu Hitoshi Murayama

3. Outline • Introduction • Current Status of Neutrino Oscillation • Main Scientific Questions • Majorana vs Dirac • The last mixing angle and CP violation • Conclusion LBNLnu Hitoshi Murayama

4. Current Status of Neutrino Oscillation

5. Rare Effects from High-Energies • Effects of physics beyond the SM as effective operators • Can be classified systematically (Weinberg) LBNLnu Hitoshi Murayama

6. Unique Role of Neutrino Mass • Lowest order effect of physics at short distances • Tiny effect (mn/En)2~(eV/GeV)2=10–18! • Interferometry (i.e., Michaelson-Morley)! • Need coherent source • Need interference (i.e., large mixing angles) • Need long baseline Nature was kind to provide all of them! • “neutrino interferometry” (a.k.a. neutrino oscillation) a unique tool to study physics at very high scales LBNLnu Hitoshi Murayama

7. MNS matrix • Standard parameterization of Maki-Nakagawa-Sakata matrix for 3 generations atmospheric solar ??? LBNLnu Hitoshi Murayama

8. What we learned in 2001–2 • Atmospheric nm is lost (>10s), converted most likely to nt(>99%CL) (SK, MACRO, SOUDAN-II) • Solar ne is converted to either nm or nt(>5s) (SNO) • Reactor anti-ne are lost (99.95%CL) (KamLAND) • Only the LMA solution left for solar neutrinos • Tiny neutrino mass: the first evidence for incompleteness of Minimal Standard Model LBNLnu Hitoshi Murayama

9. Only ne produced in the Sun Wrong Neutrinosnm,t are coming from the Sun! Somehow some of ne were converted to nm,t on their way from the Sun’s core to the detector  neutrino oscillation! SNO Result LBNLnu Hitoshi Murayama

10. KamLAND result • First terrestrial expt relevant to solar neutrino problem • KamLAND will exclude or verify LMA definitively Dec 2002 Expected #events: 86.8±5.6 Background #events: 0.95±0.99 Observed #events: 54 No oscillation hypothesis Excluded at 99.95% LBNLnu Hitoshi Murayama

11. Summary of Neutrino Oscillation Before SNO and KamLAND Dec 2002 with SNO and KamLAND LBNLnu Hitoshi Murayama

12. Three-generation • Solar, reactor & atmospheric n oscillations easily accommodated within three generations • sin22q23near maximal, Dm2atm ~ 310–3eV2 • sin22q12large, Dm2solar ~ 5–2010–5eV2 • sin22q13=|Ue3|2< 0.05 from CHOOZ, Palo Verde • Because of small sin22q13, solar (reactor) & atmospheric n oscillations almost decouple LBNLnu Hitoshi Murayama

13. Seven Questions • Dirac or Majorana? • Absolute mass scale? • How small is q13? • CP Violation? • Mass hierarchy? • Verify Oscillation? • LSND? Sterile neutrino(s)? CPT violation? LBNLnu Hitoshi Murayama

14. Seven Questions • Dirac or Majorana? • Absolute mass scale? • How small is q13? • CP Violation? • Mass hierarchy? • Verify Oscillation? • LSND? Sterile neutrino(s)? CPT violation? LBNLnu Hitoshi Murayama

15. Extended Standard Model • Massive Neutrinos  Minimal SM incomplete • How exactly do we extend it? • Abandon either • Minimality: introduce new unobserved light degrees of freedom (right-handed neutrinos) • Lepton number: abandon distinction between neutrinos and anti-neutrinos and hence matter and anti-matter • Dirac or Majorana neutrino • Without knowing which, we don’t know how to extend the Standard Model LBNLnu Hitoshi Murayama

16. Theoretical Bias:Seesaw Mechanism • Why is neutrino mass so small? • Need right-handed neutrinos to generate neutrino mass , but nR SM neutral To obtain m3~(Dm2atm)1/2, mD~mt, M3~1015GeV (GUT!) Majorana Neutrinos LBNLnu Hitoshi Murayama

17. Neutrinoless Double-beta Decay • The only known practical approach to discriminate Majorana vs Dirac neutrinos 0nbb: nn  ppe–e– with no neutrinos • Matrix element  <mne>=SimniUei2 • Current limit |<mne>| ≤ about 1eV • m3~(Dm223)1/2≈0.05eV looks a promising goal • However, m3Ue32<<m3 and we can ignore m3 • Fortunately, Ue12 and Ue22 cannot cancel exactly because the maximal angle excluded by SNO: Ue12–Ue22=cos22q12>0.07 (1s) LBNLnu Hitoshi Murayama

18. Three Types of Mass Spectrum • Degenerate • All three around >0.1eV with small splittings • Possible even after WMAP+2dF: m<0.23eV • May be confirmed by KATRIN, cosmology • |<mne>|=|SimniUei2|>m cos22q12>0.07m • Inverted • m3~0, m1~m2~(Dm223)1/2≈0.05eV • May be confirmed by long-baseline experiment with matter effect • |<mne>|=|SimniUei2|>(Dm223)1/2 cos22q12>0.0035eV • Normal • m1~m2~0, m3~(Dm223)1/2≈0.05eV • |<mne>|=|SimniUei2| may be zero even if Majorana LBNLnu Hitoshi Murayama

19. Seven Questions • Dirac or Majorana? • Absolute mass scale? • How small is q13? • CP Violation? • Mass hierarchy? • Verify Oscillation? • LSND? Sterile neutrino(s)? CPT violation? LBNLnu Hitoshi Murayama

20. Now that LMA is confirmed... • Dream case for neutrino oscillation physics! • Dm2solar within reach of long-baseline expts • Even CP violation may be probable • neutrino superbeam • muon-storage ring neutrino factory • Possible only if: • Dm122, s12 large enough (LMA) • q13 large enough LBNLnu Hitoshi Murayama

21. Shootout (Lindner) LBNLnu Hitoshi Murayama

22. LBNLnu Hitoshi Murayama

23. LBNLnu Hitoshi Murayama

24. q13 decides the future • The value of q13 crucial for the future of neutrino oscillation physics • Determines the required facility/parameters/baseline/energy • Two paths to determine q13 • Long-baseline accelerator neutrino oscillation • Reactor neutrino experiment with two detectors LBNLnu Hitoshi Murayama

25. Seven Questions • Dirac or Majorana? • Absolute mass scale? • How small is q13? • CP Violation? • Mass hierarchy? • Verify Oscillation? • LSND? Sterile neutrino(s)? CPT violation? LBNLnu Hitoshi Murayama

26. Even atmospheric neutrino data do not show “oscillation” yet  MINOS, J-PARC Dm223, q23, mass hierarchy and q13 KamLAND data is consistent with overall suppression  continued running  Dm212 Verify Oscillation LBNLnu Hitoshi Murayama

27. Solar neutrino data suggest energy-dependent survival probability  tests MSW effect  q12  Helps interpretation of CP violation, double beta decay data Low-Energy Solar Neutrinos 1% 7% 20% LBNLnu Hitoshi Murayama

28. Seven Questions • Dirac or Majorana? • Absolute mass scale? • How small is q13? • CP Violation? • Mass hierarchy? • Verify Oscillation? • LSND? Sterile neutrino(s)? CPT violation? LBNLnu Hitoshi Murayama

29. Sterile neutrinos are strongly constrained by the combination of all existing data and WMAP+2dF CPT violation is strongly constrained by SNO+KamLAND If LSND correct, all previous measurements need to be re-examined by a collection of short-, medium- and long-baseline experiments. Possibly mini-muon-storage ring. If LSND right,All hell breaks loose LBNLnu Hitoshi Murayama

30. Seven Questions • Dirac or Majorana? • Absolute mass scale? • How small is q13? • CP Violation? • Mass hierarchy? • Verify Oscillation? • LSND? Sterile neutrino(s)? CPT violation? Specific recommendations to attack these questions in the context of LBNL LBNLnu Hitoshi Murayama