Status of Neutrino Science Hitoshi Murayama LBNLnu April

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

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 2

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

Current Status of Neutrino Oscillation LBNLnu Hitoshi Murayama

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

Unique Role of Neutrino Mass • Lowest order effect of physics at short distances • Tiny effect (mn/En)2~(e. V/Ge. V)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 6

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

What we learned in 2001– 2 • Atmospheric nm is lost (>10 s), converted most likely to nt (>99%CL) (SK, MACRO, SOUDAN-II) • Solar ne is converted to either nm or nt (>5 s) (SNO) • Reactor anti-ne are lost (99. 95%CL) (Kam. LAND) • Only the LMA solution left for solar neutrinos • Tiny neutrino mass: the first evidence for incompleteness of Minimal Standard Model LBNLnu Hitoshi Murayama 8

SNO Result • Only ne produced in the Sun • Wrong Neutrinos nm, 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! LBNLnu Hitoshi Murayama 9

Kam. LAND result • First terrestrial expt relevant to solar neutrino problem • Kam. LAND 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 10

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

Three-generation • Solar, reactor & atmospheric n oscillations easily accommodated within three generations • sin 22 q 23 near maximal, Dm 2 atm ~ 3 10– 3 e. V 2 • sin 22 q 12 large, Dm 2 solar ~ 5– 20 10– 5 e. V 2 • sin 22 q 13=|Ue 3|2< 0. 05 from CHOOZ, Palo Verde • Because of small sin 22 q 13, solar (reactor) & atmospheric n oscillations almost decouple LBNLnu Hitoshi Murayama 12

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

Seven Questions • • Dirac or Majorana? Absolute mass scale? How small is q 13? CP Violation? Mass hierarchy? Verify Oscillation? LSND? Sterile neutrino(s)? CPT violation? LBNLnu Hitoshi Murayama 14

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 15

Theoretical Bias: Seesaw Mechanism • Why is neutrino mass so small? • Need right-handed neutrinos to generate neutrino mass , but n. R SM neutral To obtain m 3~(Dm 2 atm)1/2, m. D~mt, M 3~1015 Ge. V (GUT!) Majorana Neutrinos LBNLnu Hitoshi Murayama 16

Neutrinoless Double-beta Decay • The only known practical approach to discriminate Majorana vs Dirac neutrinos 0 nbb: nn ppe–e– with no neutrinos • Matrix element <mne>=Simni. Uei 2 • Current limit |<mne>| ≤ about 1 e. V • m 3~(Dm 223)1/2≈0. 05 e. V looks a promising goal • However, m 3 Ue 32<<m 3 and we can ignore m 3 • Fortunately, Ue 12 and Ue 22 cannot cancel exactly because the maximal angle excluded by SNO: Ue 12 –Ue 22=cos 22 q 12>0. 07 (1 s) LBNLnu Hitoshi Murayama 17

Three Types of Mass Spectrum • Degenerate – – All three around >0. 1 e. V with small splittings Possible even after WMAP+2 d. F: m<0. 23 e. V May be confirmed by KATRIN, cosmology |<mne>|=|Simni. Uei 2|>m cos 22 q 12>0. 07 m • Inverted – m 3~0, m 1~m 2~(Dm 223)1/2≈0. 05 e. V – May be confirmed by long-baseline experiment with matter effect – |<mne>|=|Simni. Uei 2|>(Dm 223)1/2 cos 22 q 12>0. 0035 e. V • Normal – m 1~m 2~0, m 3~(Dm 223)1/2≈0. 05 e. V – |<mne>|=|Simni. Uei 2| may be zero even if Majorana LBNLnu Hitoshi Murayama 18

Seven Questions • • Dirac or Majorana? Absolute mass scale? How small is q 13? CP Violation? Mass hierarchy? Verify Oscillation? LSND? Sterile neutrino(s)? CPT violation? LBNLnu Hitoshi Murayama 19

Now that LMA is confirmed. . . • Dream case for neutrino oscillation physics! • Dm 2 solar within reach of long-baseline expts • Even CP violation may be probable – neutrino superbeam – muon-storage ring neutrino factory • Possible only if: – Dm 122, s 12 large enough (LMA) – q 13 large enough LBNLnu Hitoshi Murayama 20

Shootout (Lindner) LBNLnu Hitoshi Murayama 21

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q 13 decides the future • The value of q 13 crucial for the future of neutrino oscillation physics • Determines the required facility/parameters/baseline/energy • Two paths to determine q 13 – Long-baseline accelerator neutrino oscillation – Reactor neutrino experiment with two detectors LBNLnu Hitoshi Murayama 24

Seven Questions • • Dirac or Majorana? Absolute mass scale? How small is q 13? CP Violation? Mass hierarchy? Verify Oscillation? LSND? Sterile neutrino(s)? CPT violation? LBNLnu Hitoshi Murayama 25

Verify Oscillation • Even atmospheric neutrino data do not show “oscillation” yet MINOS, J-PARC Dm 223, q 23, mass hierarchy and q 13 • Kam. LAND data is consistent with overall suppression continued running Dm 212 LBNLnu Hitoshi Murayama 26

Low-Energy Solar Neutrinos • Solar neutrino data suggest energydependent survival probability tests MSW effect q 12 Helps interpretation of CP violation, double beta decay data LBNLnu Hitoshi Murayama 1% 7% 20% 27

Seven Questions • • Dirac or Majorana? Absolute mass scale? How small is q 13? CP Violation? Mass hierarchy? Verify Oscillation? LSND? Sterile neutrino(s)? CPT violation? LBNLnu Hitoshi Murayama 28

If LSND right, All hell breaks loose • Sterile neutrinos are strongly constrained by the combination of all existing data and WMAP+2 d. F • CPT violation is strongly constrained by SNO+Kam. LAND • If LSND correct, all previous measurements need to be reexamined by a collection of short-, medium- and longbaseline experiments. Possibly mini-muon-storage ring. LBNLnu Hitoshi Murayama 29

Seven Questions • Dirac or Majorana? • Absolute mass scale? • How small is q 13? • CP Violation? • Mass hierarchy? • Verify Oscillation? • LSND? Sterile neutrino(s)? CPT violation? Specific recommendations to attack these questions in the context of LBNLnu Hitoshi Murayama 30