#### Transcript Document 7187508

Neutrino Physics Hitoshi Murayama Taiwan Spring School March 27, 2002 中性微子物理 村山 斉 台湾春期学校 二千二年三月二十七日 Neutrinos are Everywhere 3 “Wimpy and Abundant” Neutrinos are Everywhere • They come from the Big Bang: – When the Universe was hot, neutrinos were created equally with any other particles – They are still left over: ~300 neutrinos per cm3 • They come from the Sun: – Trillions of neutrinos going through your body every second • They are shy: – If you want to stop them, you need to stack up lead shield up to three light-years 4 Outline • • • • Introduction Neutrinos in the Standard Model Atmospheric Neutrinos Solar Neutrinos 5 Neutrinos in the Standard Model Puzzle with Beta Spectrum • Three-types of radioactivity: a, b, g • Both a, g discrete spectrum because Ea, g = Ei – Ef • But b spectrum continuous F. A. Scott, Phys. Rev. 48, 391 (1935) Bohr: At the present stage of atomic theory, however, we may say that we have no argument, either empirical or theoretical, for upholding the energy principle in the case of b-ray disintegrations 7 Desperate Idea of Pauli 8 Three Kinds of Neutrinos • There are three • And no more 9 Neutrinos are Left-handed 10 Neutrinos must be Massless • All neutrinos left-handed massless • If they have mass, can’t go at speed of light. • Now neutrino right-handed?? contradiction can’t be massive 11 Anti-Neutrinos are Right-handed • CPT theorem in quantum field theory – C: interchange particles & antiparticles – P: parity – T: time-reversal • State obtained by CPT _ from nL must exist: nR 12 Standard Model • Therefore, neutrinos are strictly massless in the Standard Model of particle physics Finite mass of neutrinos imply the Standard Model is incomplete! • Not just incomplete but probably a lot more profound 13 Lot of effort since ‘60s Finally convincing evidence for “neutrino oscillation” Neutrinos appear to have tiny but finite mass 14 Atmospheric Neutrinos Super-Kamiokande (SuperK) • Kamioka Mine in central Japan • ~1000m underground • 50kt water • Inner Detector – 11,200 PMTs • Outer Detector – 2,000 PMTs Michael Smy 16 SuperKamiokaNDE Nucleon Decay Experiment • pe+p0, K+n, etc – So far not seen – Atmospheric neutrino main background • Cosmic rays isotropic – Atmospheric neutrino up-down symmetric 17 A half of nm lost! 18 Neutrinos’ clock • Time-dilation: the clock goes slower v2 t 1 2 c • At speed of light v=c, clock stops • But something seems to happen to neutrinos on their own • Neutrinos’ clock is going • Neutrinos must be slower than speed of light • Neutrinos must have a mass 19 The Hamiltonian • The Hamiltonian of a freely-propagating massive neutrino is simply H 2 m p2 m 2 p 2p • But in quantum mechanics, mass is a matrix in general. 22 case: 2 2 m 211 M2 2 m 21 2 m 12 2 m 22 M 1 m1 1 M 2 2 m22 2 20 Two-Neutrino Oscillation • When produced (e.g., p+m+nm), neutrino is of a particular type n m ,t 1 cos e im12t |/ 2 p 2 sin e im22t / 2 p 21 Two-Neutrino Oscillation • When produced (e.g., p+m+nm), neutrino is of a particular type 2 22 im t / 2 p im im | 22t / 2 p n m ,t 1 cos e 1 2 sin e • No longer 100% nm, partly n! • “Survival probability” for nm after t P n m nm ,t 2 2 4 m c GeV ct 2 2 1 sin 2 sin 1.27 2 c p km eV 22 Survival Probability p=1 GeV/c, sin2 2=1 m2=310–3(eV/c2)2 Half of the up-going ones get lost 23 Lower Energy 24 Lowest Energy 25 Higher Energy 26 27 More cross checks • Multi-ring events can be used to provide useful cross checks (Hall, HM) 28 29 Confirmation with Man-made neutrino beam 250km K2K experiment 818 events if no oscillation 56 events observed Deficit at 2 sigma level 30 MINOS (NuMI) OPERA/ICARUS (CNGS) • MINOS: precision measurements of (m232, sin2223) 2004– • OPERA/ICARUS @ CNGS: tau appearance in nmn 2005– • Both L~750 km, Extend reach in sin2213 • MONOLITH aims at verifying oscillation curves with atmospheric neutrinos 31 Public Interest in Neutrinos 32 33 Why does 2-flavor mixing work? • Maki-Nakagawa-Sakata matrix for 3 Ue1 Ue2 Ue3 generations n m ,t 1 Um1 U MNS Um1 Um 2 Um 3 U 1 U 2 U 3 im12t / 2 p im22t / 2 p e 2U e 3U m2 m3 e im32t / 2 p 34 Why does 2-flavor mixing work? • Maki-Nakagawa-Sakata matrix for 3 Ue1 Ue2 Ue3 generations n m ,t 1 Um1 U MNS Um1 Um 2 Um 3 U 1 U 2 U 3 im12t / 2 p im22t / 2 p e 2U e 3U m2 m3 e im32t / 2 p * * * n 1U 2 U 3U 1 2 3 n n m ,t U*1Um1 U 2Um 2 e * e im22 t / 2 p im12 t / 2 p U 3Um 3 e * im32 t / 2 p 35 Why does 2-flavor mixing work? • If m1 and m2 not very different, it reduces to the 2-flavor problem n n m ,t U*1Um1 U 2Um 2 e * U*1Um1 im22 t / 2 p U 3Um 3 e * U 2Um 2 e U 3Um 3e * e im12 t / 2 p * im12 t / 2 p im12 t / 2 p im32 t / 2 p U 3Um 3 e U 3Um 3 e * * im32 t / 2 p im32 t / 2 p 2 im 2 t / 2 p im t / 2 p 3 e sin e 1 e i 36 When is 3-flavor important? n n m ,t 2 U*iUmiUjUm*j e i mi2 m 2j t / 2 p i, j 2e U*iUmiUjUm*j sin 2 2 m m j 2 i 4p i, j m U*iUmiUjUm*j sin i, j mi2 m 2j 2p t t When all masses significantly different Anti-neutrinos: UU*, the last term flips sign Possible CP violation 37 MNS matrix • Standard parameterization of MakiNakagawa-Sakata matrix for 3 generations UMNS Ue1 Ue2 U m1 U m 2 U 1 U 2 Ue3 Um 3 U 3 1 c13 c23 s23 i s23 c23 s13e atmospheric s13e i c12 1 s12 c13 ??? s12 c12 1 solar 38 Three-generation • Solar & atmospheric n oscillations easily accommodated within three generations • sin2223 near maximal, m2atm ~ 310–3eV2 • sin2212 large, m2solar ~ 310–5eV2? • sin2213 < 0.05 from CHOOZ, Palo Verde • Because of small sin2213, solar & atmospheric n oscillations almost decouple • Need to know the solar situation, • sin2213, and mass hierarchy 39 CP Violation P(n e n m ) 2 P(n e n m ) 16s12 c12 s13 c13 s23 c23 m2 m 2 m 2 sin sin 12 L sin 13 L sin 23 L 4E 4E 4E • Possible only if: – m122, s12 large enough (LMA) – 13 large enough 40 superbeam • Existing proposals of neutrino superbeam (Debbie Harris@Snowmass2001) Name Start Year Proton Proton Neutrino Baseline Power Energy Energy (km) Years of Running CP sin 2 13 phase kton (3) (3) JHF to 2008? SuperK 0.77 MW 50GeV 0.7GeV 350km 5 yrs n JHF to 2013? HyperK 4MW 50GeV 0.7GeV 350km 2 yrs n 6 yrs n 1000 0.0025 15o CERN 2011 to UNO 4MW 2.2GeV 250MeV 130km 2 yrs n 10 yrs n 400 0.0025 40o 50 0.016 none 41 High-energy superbeam • Higher E, longer L Can study matter effect to determine the mass hierarchy (Barger, Marfatia, Whisnant@Snowmass2001) Baseline (km) Neutrino sin 2 Reach (3) 13 Energy n nbar (GeV) Sign (m232) CP phase (3) 350 1 .0013 .0016 – 20 730 2.1 .0017 .0026 – 24 1290 3.7 .0020 .0052 .04 32 1770 5 .0022 .0092 .02 40 2900 8.2 .0025 .037 .01 76 42 Solar Neutrinos How the Sun burns • The Sun emits light because nuclear fusion produces a lot of energy 2 Lsun 1 10 1 2 n 7 10 sec cm 25MeV 4p (1AU) 2 44 45 SuperK sees the Sun 46 Solar Neutrino Spectrum p p d n e e p e p d ne 7 Be p8 B 8 Be e + n e 8 7 Be e 7 Li + n e Be 2a 3 He p He + n47e e 4 We don’t get enough 48 Why? 1. Astrophysics is wrong – – pp neutrino flux tied to solar luminosity Change 7Be, 8B arbitrarily can’t fit the data 2. Some of the data are wrong – – Even if only one experiment correct, the puzzle remains Need both 1. & 2. to explain the situation 3. Something is wrong with neutrinos 49 Astrophysics wrong? Fit data with arbitrary 7Be, 8B Best fit needs negative 7Be Remember 8B is a product of 7Be! 50 Astrophysics wrong? • Helioseismology data agree well with the SSM 51 52 Josh Klein, Lepton Photon 2001 SNO comes to the rescue • SNO: ne 6 2 1 n 1.75 0.07 0.12 0.0510 cm sec 0.11 • SuperK: ne+nm,/7 6 2 1 n 2.32 0.030.08 10 cm sec 0.07 3.3 difference nm, are coming from the Sun! 53 SNO result • Total 8B flux: (5.440.99)10-9cm-2s-1 • BP2000 calculation (5.05+0.1-0.8)10-9cm-2s-1 Remarkable agreement! 54 Wrong Neutrinos • Only ne produced in the Sun • Wrong Neutrinos nm, are coming from the Sun! • Somehow some of ne were converted to nm, on their way from the Sun’s core to the detector neutrino oscillation! SNO is further studying neutral current reaction ne+nm+n Expect result in April! 55 Conclusions • Evidence for oscillation in atmoshperic neutrino very strong • More cross-checks with man-made beams • Eventually to more powerful long-baseline oscillation experiments, aiming at CP violation • Solar neutrino problem clearly not due to astrophysics 56