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L/E analysis of the atmospheric neutrino data from Super-Kamiokande

L/E analysis of the atmospheric neutrino data from Super-Kamiokande. Itaru Higuchi ICRR for Super-Kamiokande collaboration. ICRC2005 Aug, 2005. Motivation. Other models can explain zenith angle dependent muon deficit. How can we distinguish oscillation from other hypotheses ?

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L/E analysis of the atmospheric neutrino data from Super-Kamiokande

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  1. L/E analysis of the atmospheric neutrino datafrom Super-Kamiokande Itaru Higuchi ICRR for Super-Kamiokande collaboration ICRC2005 Aug, 2005

  2. Motivation • Other models can explain zenith angle dependent muon deficit. How can we distinguish oscillation from other hypotheses ? • Muon neutrino disappearance probability as a function of neutrino flight length L over neutrino energy E was studied to distinguish neutrino oscillation from other hypotheses. • A dip in the L/E distribution was observed in the data from Super-Kamiokande-I during 1489 live-days exposure. • We report preliminary result from SK-II during 627 days live-days exposure.

  3. Survive probability Dm2L Neutrino oscillation : Pmm = 1 – sin22qsin2(1.27 ) E L m Neutrino decay : Pmm = (cos2q + sin2q x exp(– ))2 2t E L 1 Neutrino decoherence : Pmm = 1 – sin22q x (1 – exp(–g0 )) 2 E Use events with high resolution in L/E The first dip can be observed • Direct evidence for oscillations • Strong constraint to oscillation parameters, especially Dm2 value

  4. Event samples in L/E analysis FC (tracks are contained inside the ID) • Single-ring , μ-like • Multi-ring , μ-like observed charge / expectation from through-going PC (deposits visible energy in the OD) OD stopping OD through-going Classify PC events using OD charge OD through-going MC • OD stopping • OD through going OD stopping MC

  5. Reconstruction of E and L Neutrino energy Neutrino flight length En Eobserved Eobserved  En Zenith angle  Flight length Neutrino energy is reconstructed from observed energy using relations based on MC simulation Neutrino flight length is estimated from zenith angle of particle direction

  6. L/E resolution cut Select events with high resolution in L/E Full oscillation 1/2 oscillation Bad L/E resolution for horizontally going events  due to large dL/dcosq low energy events  due to large scattering angle D(L/E)=70%

  7. Event summary of L/E analysis SK-I 1489 days SK-II 627 days Data MC CC nm Data MC CC nm FC single-ring multi-ring stopping through-going 1619 2105.6 (98.3%) 502 813.0 (94.2%) 114 137.0 (95.4%) 491 670.1 (99.2%) 686 876.6 (98.6%) 222 329.4 (93.6%) 51 48.5 (94.4%) 162 269.7 (99.2%) PC 2726 3725.7 Total 1121 1524.2

  8. L/E in atmospheric neutrino data Mostly upward Mostly upward SK-I FC+PC SK-II FC+PC Preliminary Null oscillation MC Null oscillation MC Mostly downward Mostly downward Best-fit expectation Best-fit expectation

  9. L/E in atmospheric neutrino data SK-I FC+PC SK-II FC+PC Best fit expectation w/ systematic errors Best fit expectation w/ systematic errors Preliminary First dip is observed as expected from neutrino oscillation

  10. Constraint to neutrino oscillation parameters SK-I SK-II Preliminary Best fit results Dm2=2.4x10-3,sin22q=1.00 c2min=37.8/40 d.o.f (sin22q=1.02, c2min=37.7/40 d.o.f) Dm2=2.6x10-3,sin22q=1.00 c2min=54.8/40 d.o.f (sin22q=1.02, c2min=54.7/40 d.o.f) 1.9x10-3 < Dm2 < 3.0x10-3 eV2 0.90 < sin22qat 90% C.L. 1.8x10-3 < Dm2 < 4.0x10-3 eV2 0.83 < sin22qat 90% C.L.

  11. Constraint to neutrino oscillation parameters SK-I SK-II Preliminary Best fit results Dm2=2.4x10-3,sin22q=1.00 c2min=37.8/40 d.o.f (sin22q=1.02, c2min=37.7/40 d.o.f) Dm2=2.6x10-3,sin22q=1.00 c2min=54.8/40 d.o.f (sin22q=1.02, c2min=54.7/40 d.o.f) 1.9x10-3 < Dm2 < 3.0x10-3 eV2 0.90 < sin22qat 90% C.L. 1.8x10-3 < Dm2 < 4.0x10-3 eV2 0.83 < sin22qat 90% C.L.

  12. Constraint to neutrino oscillation parameters SK-I SK-II Preliminary Best fit results Dm2=2.4x10-3,sin22q=1.00 c2min=37.8/40 d.o.f (sin22q=1.02, c2min=37.7/40 d.o.f) Dm2=2.6x10-3,sin22q=1.00 c2min=54.8/40 d.o.f (sin22q=1.02, c2min=54.7/40 d.o.f) 1.9x10-3 < Dm2 < 3.0x10-3 eV2 0.90 < sin22qat 90% C.L. 1.8x10-3 < Dm2 < 4.0x10-3 eV2 0.83 < sin22qat 90% C.L.

  13. Tests for neutrino decay & decoherence SK-I SK-II Oscillation Decay Decoherence Dc2= c2decay-c2osc =11.4(3.4σ) Dc2 = c2decoherence-c2osc =14.6(3.8 σ) Dc2= c2decay-c2osc =7.9(2.8σ) Dc2 = c2decoherence-c2osc =8.7(2.9 σ) Preliminary cannot be explained by alternative hypotheses

  14. Conclusions Measurement of L/E dependence of flavor transition probability First dip was observed as expected from neutrino oscillation  cannot be explained by alternative hypotheses  gives strong constraint to neutrino oscillation parameters The results from SK-I and SK-II agree well. Next step : combine SK-I and SK-II

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