Status of Neutrino Science Hitoshi Murayama LBNLnu April 11, 2003

LBNLnu Hitoshi Murayama2 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 Murayama3 Outline Introduction Current Status of Neutrino Oscillation Main Scientific Questions Majorana vs Dirac The last mixing angle and CP violation Conclusion

Current Status of Neutrino Oscillation

LBNLnu Hitoshi Murayama5 Rare Effects from High-Energies Effects of physics beyond the SM as effective operators Can be classified systematically (Weinberg)

LBNLnu Hitoshi Murayama6 Unique Role of Neutrino Mass Lowest order effect of physics at short distances Tiny effect (m /E ) 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 Murayama7 MNS matrix Standard parameterization of Maki- Nakagawa-Sakata matrix for 3 generations atmospheric ??? solar

LBNLnu Hitoshi Murayama8 What we learned in 2001–2 Atmospheric  is lost (>10  ), converted most likely to  (>99%CL) (SK, MACRO, SOUDAN-II) Solar e is converted to either  or  (>5  ) (SNO) Reactor anti- e 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 Murayama9 SNO Result Only e produced in the Sun Wrong Neutrinos   are coming from the Sun! Somehow some of e were converted to  on their way from the Sun’s core to the detector  neutrino oscillation!

LBNLnu Hitoshi Murayama10 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 Murayama11 Summary of Neutrino Oscillation Before SNO and KamLAND Dec 2002 with SNO and KamLAND

LBNLnu Hitoshi Murayama12 Three-generation Solar, reactor & atmospheric oscillations easily accommodated within three generations sin 2 2  23 near maximal,  m 2 atm ~ 3  10 –3 eV 2 sin 2 2  12 large,  m 2 solar ~ 5–20  10 –5 eV 2 sin 2 2  13 =|U e3 | 2 < 0.05 from CHOOZ, Palo Verde Because of small sin 2 2  13, solar (reactor) & atmospheric oscillations almost decouple

LBNLnu Hitoshi Murayama13 Seven Questions Dirac or Majorana? Absolute mass scale? How small is  13 ? CP Violation? Mass hierarchy? Verify Oscillation? LSND? Sterile neutrino(s)? CPT violation?

LBNLnu Hitoshi Murayama14 Seven Questions Dirac or Majorana? Absolute mass scale? How small is  13 ? CP Violation? Mass hierarchy? Verify Oscillation? LSND? Sterile neutrino(s)? CPT violation?

LBNLnu Hitoshi Murayama15 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 Murayama16 Theoretical Bias: Seesaw Mechanism Why is neutrino mass so small? Need right-handed neutrinos to generate neutrino mass To obtain m 3 ~(  m 2 atm ) 1/2, m D ~m t, M 3 ~10 15 GeV (GUT!) Majorana Neutrinos, but R SM neutral

LBNLnu Hitoshi Murayama17 Neutrinoless Double-beta Decay The only known practical approach to discriminate Majorana vs Dirac neutrinos 0  : nn  ppe – e – with no neutrinos Matrix element  =  i m i U ei 2 Current limit | | ≤ about 1eV m 3 ~(  m 2 23 ) 1/2 ≈0.05eV looks a promising goal However, m 3 U e3 2 <<m 3 and we can ignore m 3 Fortunately, U e1 2 and U e2 2 cannot cancel exactly because the maximal angle excluded by SNO: U e1 2 –U e2 2 =cos 2 2  12 >0.07 (1  )

LBNLnu Hitoshi Murayama18 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 –| |=|  i m i U ei 2 |>m cos 2 2  12 >0.07m Inverted –m 3 ~0, m 1 ~m 2 ~(  m 2 23 ) 1/2 ≈0.05eV –May be confirmed by long-baseline experiment with matter effect –| |=|  i m i U ei 2 |>(  m 2 23 ) 1/2 cos 2 2  12 >0.0035eV Normal –m 1 ~m 2 ~0, m 3 ~(  m 2 23 ) 1/2 ≈0.05eV –| |=|  i m i U ei 2 | may be zero even if Majorana

LBNLnu Hitoshi Murayama19 Seven Questions Dirac or Majorana? Absolute mass scale? How small is  13 ? CP Violation? Mass hierarchy? Verify Oscillation? LSND? Sterile neutrino(s)? CPT violation?

LBNLnu Hitoshi Murayama20 Now that LMA is confirmed... Dream case for neutrino oscillation physics!  m 2 solar within reach of long-baseline expts Even CP violation may be probable –neutrino superbeam –muon-storage ring neutrino factory Possible only if: –  m 12 2, s 12 large enough (LMA) –  13 large enough

LBNLnu Hitoshi Murayama21 Shootout (Lindner)

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LBNLnu Hitoshi Murayama24  13 decides the future The value of  13 crucial for the future of neutrino oscillation physics Determines the required facility/parameters/baseline/energy Two paths to determine  13 –Long-baseline accelerator neutrino oscillation –Reactor neutrino experiment with two detectors

LBNLnu Hitoshi Murayama25 Seven Questions Dirac or Majorana? Absolute mass scale? How small is  13 ? CP Violation? Mass hierarchy? Verify Oscillation? LSND? Sterile neutrino(s)? CPT violation?

LBNLnu Hitoshi Murayama26 Verify Oscillation Even atmospheric neutrino data do not show “oscillation” yet  MINOS, J-PARC   m 2 23,  23, mass hierarchy and  13 KamLAND data is consistent with overall suppression  continued running   m 2 12

LBNLnu Hitoshi Murayama27 Low-Energy Solar Neutrinos Solar neutrino data suggest energy- dependent survival probability  tests MSW effect  12  Helps interpretation of CP violation, double beta decay data 7% 1% 20%

LBNLnu Hitoshi Murayama28 Seven Questions Dirac or Majorana? Absolute mass scale? How small is  13 ? CP Violation? Mass hierarchy? Verify Oscillation? LSND? Sterile neutrino(s)? CPT violation?

LBNLnu Hitoshi Murayama29 If LSND right, All hell breaks loose 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.

LBNLnu Hitoshi Murayama30 Seven Questions Dirac or Majorana? Absolute mass scale? How small is  13 ? CP Violation? Mass hierarchy? Verify Oscillation? LSND? Sterile neutrino(s)? CPT violation?  Specific recommendations to attack these questions in the context of LBNL