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Atmospheric Neutrino Oscillations in SK-I

Atmospheric Neutrino Oscillations in SK-I. An Updated Analysis. Alec Habig, Univ. of Minnesota Duluth for the Super-Kamiokande Collaboration. With much help from Masaki Ishitsuka & Mark Messier. Updated Analysis. All “SK-I” data (April 1996-July 2001) reanalyzed (1489 live-days)

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Atmospheric Neutrino Oscillations in SK-I

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  1. Atmospheric Neutrino Oscillations in SK-I An Updated Analysis Alec Habig, Univ. of Minnesota Duluth for the Super-Kamiokande Collaboration With much help from Masaki Ishitsuka & Mark Messier

  2. Updated Analysis • All “SK-I” data (April 1996-July 2001) reanalyzed (1489 live-days) • Ring selection, Particle ID, multi-ring fits improved • Up-m reduction automated and fitting improved (1646 live-days) • Monte Carlo predictions improved • New 2001 Honda 3D n flux (was Honda 1995) • Fermi Momentum, Axial Mass changed to better match K2K near detector n interaction data • (pF now flat, MA for QE, single p from 1.01.1) • New calibs. improve Outer Detector, H2O parameters in detector simulation (GEANT 3 based) Alec Habig

  3. Flux Changes • Honda 1995 1D to Honda 2001 3D • Absolute normalization lower • “3D” enhancement • At low energies • Near the horizon • But at low E, nm following angle is large • Smears out the peak near horizon • So 3D-ness changes little for Super-K (see next slide…) Alec Habig

  4. Sub-GeV Data Sub-GeV (stat.) (syst.) (note no “3D” horizon peak) No cos(q) shape information at the lowest energies, only flavor ratio is useful At higher energies, nm directionality better preserved plus shorter L nm no longer oscillate: cos(q) shape information very useful Key:  Data  MC (no osc.)  MC (best fit) Alec Habig

  5. Multi-GeV data n baseline L: 12800 6200 700 40 15 km Multi GeV+PC (stat.) (syst.) (stat.) (syst.) At even higher energies, n flux up/down symmetric and low-L nm do not have time to disappear. Compare to Ae-like= -0.0200.0430.005 MC Am-like= -0.0030.0050.009 Observed Am-like 9.5s from no-oscillation prediction! Key:  Data  MC (no osc.)  MC (best fit) Alec Habig

  6. More Data SK m nm SK m nm En ~10 GeV Up through going m - • More nm, different En and systematics Measured flux: nm+Nm+np (stat.) (syst.) Theoretical calc: En~100 GeV (theo.) Up stopping m - Measured flux: nm+Nm+np (stat.) (syst.) Theoretical calc: Key:  Data  MC (no osc.)  MC (best fit) (theo.) Alec Habig

  7. New Oscillation Results • For nmnt oscillation: • Best fit: sin2(2q)=1.0, Dm2=2.0x10-3 eV2 • c2 = 170.8/170 dof • 90% c.l. region: • sin2(2q)>0.9 • 1.3 < Dm2 < 3.0x10-3 eV2 Contours represent oscillation hypotheses which fit the observed data less well with a Dc2 corresponding to: Alec Habig

  8. Difference from Previous Results • Small improvements + the same data: • but the end result has changed by more than you might expect • What happened? • (Note this figure is highly zoomed) 90% CL regions Old result @2.5x10-3 New result @2x10-3 Preliminary Alec Habig

  9. Effects of Improvements on Fit • Changes each of which caused Dm2 region to move slightly down: • n flux change (Honda 19952001) • n interaction model (pF flat, MA 1.01.1) • Improved detector simulation (OD, H2O calib.) • Improved event reconstruction (Particle ID, ring selection, up-m fitting) • Net effect on c2 surface of several small changes in same direction is larger Alec Habig

  10. Sub-Sample Consistency • Check oscillation fits using different classes of data independently – allowed regions all overlap best fit • The low energy sub-sample’s only handle on oscillations is the m/e flavor ratio • Used to be high (alone!), is now consistent with other sub-samples Note open-ended “swoosh” shape of a one-parameter flavor ratio fit to two osc. parameters (lowest E event sub-sample) Alec Habig

  11. Unusual Models • Ways to make nm disappear without nm,nt flavor oscillations include: • Lorentz inv. violation • n decay, decoherence • Fits using all available SK n data strongly constrain many such models • Hard for model to get good fit over 5 orders of mag. in E and 4 in L • Long t nm decay and nm decoherence disfavored but not eliminated Data Used: (diff. from std.) (FC+PC (cut into 2 samples @Evis = 5 GeV)+NC+multiring+up-m, 195 bins, 190 d.o.f.) Alec Habig

  12. nm to nsterile? • High energy n experience matter effects which suppress oscillations to sterile n • Matter effects not seen in up-m or high-energy PC data • Reduction in neutral current interactions also not seen • constrains ns component of nm disappearance oscillations • Pure nmns disfavored • ns fraction < 20% at 90% c.l. Alec Habig

  13. CPT Violation • Do nm oscillate differently than nm? • SK cannot tell the difference between nm and nm event-by-event • But we see the sum of the two • One behaving very differently would show up in the total Alec Habig

  14. Summary • nmnt oscillations fit the data better than other means of making nm disappear • Best fit value is (Dm2 = 2.0x10-3 eV2, sin2(2q) = 1.0) • 1.3 < Dm2 < 3.0x10-3 eV2, sin2(2q) > 0.9 @ 90% c.l. • Analysis improvements to • n interaction & flux models • Detector simulation • Event reconstruction • No one improvement drove the changes to the final fit • Each contributed a little in the same direction • All data sub-samples now individually consistent with the overall fit The presenter gratefully acknowledges support for this presentation from the National Science Foundation via its RUI grant #0098579, and from The Research Corporation’s Cottrell College Science Award Alec Habig

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