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Super-Kamiokande Atmospheric Neutrino Results

Super-Kamiokande Atmospheric Neutrino Results. Kimihiro Okumura ICRR Univ. of Tokyo ( okumura@icrr.u-tokyo.ac.jp) 11-September-2005 C2CR2005, Prague. Outline. Super-Kamiokande-I Results new n m → n t oscillation analysis search for tau neutrinos search for q 13 neutrino flux study

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Super-Kamiokande Atmospheric Neutrino Results

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  1. Super-Kamiokande Atmospheric Neutrino Results Kimihiro Okumura ICRR Univ. of Tokyo (okumura@icrr.u-tokyo.ac.jp) 11-September-2005 C2CR2005, Prague C2CR2005, Prague

  2. Outline • Super-Kamiokande-I Results • new nm→nt oscillation analysis • search for tau neutrinos • search for q13 • neutrino flux study • Status of Super-Kamiokande-II Analysis C2CR2005, Prague

  3. SK-II SK-III accident reconstruction SK-II PMT enclosure : Acrylic (front) and Fiberglass (back) 5182 19% SK-III will start on June 2006. Super-Kamiokande 1996199719981999 20002001200220032004200520062007 SK-I • 50kton cylindrical water Cherenkov detector(22.5kt fiducial vol.) • 1000m underground(2700m water equiv.) • optically separated into ID and OD SK-I 11146 Num. of inner detector PMTs 40% Photocathod coverage C2CR2005, Prague

  4. Fully Contained (En ~1GeV, nenm) Partially Contained (En ~10GeV, nm) Stopping m (En ~10GeV, nm) Through-going m(En ~100GeV, nm) Observation of Atmospheric Neutrino Event classification sensitive energy: 0.1GeV ~ 10TeV C2CR2005, Prague

  5. < < > > Zenith Angle Distributions (SK-I) nm–nt oscillation (best fit) null oscillation FC and PC : 1489 days Up-going m : 1646 days e-like m-like Preliminary C2CR2005, Prague

  6. Previous oscillation analysis Allowed region of previous zenith and L/E • Question: Can single analysis give the best sin2(2q) and Dm2 ? Zenith angle analysis : UP/DOWN ~ sin2(2q) good for sin2(2q) Number of events cosq L/E analysis : dip ~ l/2 good for Dm2 Data / MC C2CR2005, Prague

  7. Full oscillation 1/2 osci. Oscillation analysis with finer binning Important energy range to see the oscillation dip = multi-GeV Finer energy bins for multi-GeV events previous zenith (180bins) Expected sensitivity with 5yr MC (sin22q, Dm2)truth = (1.00, 2.510-3 eV2) L/E finer binning (370bins) zenith angle analysis with finer energy binning gives better sensitivity for both sin2(2q) and Dm2 C2CR2005, Prague

  8. Preliminary 90% CL allowed region: sin22q > 0.93 2.0 < Dm2 < 3.0×10-3eV2 Allowed region with finer binning Previous zenith-angle analysis L/E analysis C2CR2005, Prague

  9. Search for CC nt events CC nt events nt CC ntMC hadrons t nt hadrons nt events are accompanied with many hadrons event topology similar to other hadronic events  likelihood (or NN) analysis Only ～ 1.0 CC ntFC events/kton・yr ntappears only for up-going events  use down-going events for control sample C2CR2005, Prague

  10. Tau-like events selection criteria • Visible energy > 1.33 GeV (multi-GeV energy) • Multi-ring events (event w/ hadron particles) • Most energetic ring is e-like (showering event) log(likelihood) > 0 or NN > 0.5 C2CR2005, Prague

  11. Likelihood variables Preliminary Down-going data Max distance from primary and decay-e vertex t MC visible energy Down-going nm, ne MC Sphericity in the lab fame Max. momentum for m-like ring Clustered sphericity in the center of mass frame Number of candidate rings C2CR2005, Prague

  12. Tau likelihood distributions downward upward Preliminary Cut Cut DATA BG-MC tau-MC DATA BG-MC tau-MC (×1.82t MC) Number of events t-likelihood t-likelihood Tau-like events : Likelihood > 0 C2CR2005, Prague

  13. Zenith angle dist. and fit results NN analysis Likelihood analysis Preliminary ×1.93 t-MC Data ×1.82 t-MC Data Number of events nm, ne, & NC background nm, ne, & NC background cosqzenith cosqzenith Fitted # of t events Expected # of t events C2CR2005, Prague

  14. 1+multi-ring, e-like, 2.5 - 5 GeV Electron appearance s213=0.05 s213=0.00 null oscillation Search for non-zero q13 Three flavor oscillation analysis with Dm2solar=0 assumption : • Non-zero q13 will enhance nm→ne oscillation in multi-GeV energy due to matter effect in Earth • Electron appearance is expected in upward-going events P(nm →ne) cosqzenith cosqzenith Neutrino Energy (GeV) C2CR2005, Prague

  15. Multi-GeV electrons Zenith angle UP/DOWN asymmetry Preliminary Data single-Ring electron No oscillation Three flavor best fit (normal hierarchy) multi-Ring electron • No significant excess due to matter effect in upward-going multi-GeV electron sample C2CR2005, Prague

  16. Allowed region for q13 Preliminary • Distributions are best fitted when sin2(q13)=0 • Consistent with two flavor nm nt oscillation • sin2(q13)<0.14 allowed in 90% C.L. from SK-I data excluded by CHOOZ 99%CL Normal hierarchy (Dm2>0) 90%CL Dm2 (eV2) sin2q13 c2min/ndf = 376.82/368 @(2.5x10-3, 0.5, 0.0) sin2q23 sin2q13 C2CR2005, Prague

  17. Atmospheric n flux measurement Neutrino flux calculation cosmic-ray proton flux • Recent neutrino flux calculations have improved due to accurate measurement of comic-ray protons / muons • Approximately 20% difference still exists among flux models in higher energies nm C2CR2005, Prague

  18. ne and nm energy spectrum Preliminary • SK-I ne and nm event rates are compared with expectation in each energy range • Neutrino energies are estimated from simulation • Neutrino oscillation included for nm expected • nm→nt(Dm2, sin22q) = (2.5x10-3 eV2,1.0) assumed data expectation sub-GeV Events / yr / GeV ne multi-GeV multi-GeV nm sub-GeV Events / yr / GeV PC upmu-stop upmu-thru Neutrino energy(GeV) C2CR2005, Prague

  19. Comparison with flux models Preliminary ne • Neutrino flux models: • HKKM04 Phys. Rev. D70 043008 (2004) • Bartol Phys. Rev. D70 023006 (2004) • Fluka hep-ph/0305208 • Systematic uncertainties: • detector efficiency • n cross section ~10% • n oscillation ~4% for nm • Results: • absolute flux and spectrum are consistent within systematic errors • HKKM04 and Fluka under-estimated high energy nm flux Data / Expectation nm Error bar : (stat.)2+(sys.)2 C2CR2005, Prague

  20. New HKKM flux calculation Preliminary • HKKM flux revised: • modified hadron interaction model • see Dr. Honda’s talk • Agreement in high energy nm becomes better ne Data / Expectation nm Error bar : (stat.)2+(sys.)2 C2CR2005, Prague

  21. < < > > Zenith Angle Distributions (SK-II) nm–nt oscillation (best fit) null oscillation FC and PC : 627 days Up-going m : 609 days e-like m-like Preliminary C2CR2005, Prague

  22. Contours for SK-II SK-II SK-I Preliminary Preliminary SK-II data are consistent with SK-I data SK-I + SK-II combined analysis : next step C2CR2005, Prague

  23. SK-II L/E analysis L/E analysis was carried out for the SK-II data with the identical selection criteria as those in SK-I. SK-II SK-I Preliminary Decoh. Decay Osc. Consistent with SK-I. Oscillation still gives the best fit to the data. C2CR2005, Prague

  24. Summary • SK-I analysis results: • New nm→ nt oscillation analysis with finer binning gives more stringent constraint : • sin22q > 0.93, 2.0<Dm2<3.0x10-3 eV2 (90%C.L.) • Data are consistent with nt appearance • No evidence for multi-GeV electron appearance due to non-zero q13 • Neutrino flux calculation models are compared and consistent with data • SK-II data was analyzed independently and consistent with SK-I C2CR2005, Prague

  25. End

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