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Recent Results from Super-Kamiokande on Atmospheric Neutrino Measurements

Recent Results from Super-Kamiokande on Atmospheric Neutrino Measurements. Choji Saji ICRR,Univ. of Tokyo for the Super-Kamiokande collaboration. ICHEP 2004, Beijing. Contents. Atmospheric neutrino oscillation studies using full Super-Kamiokande I(SK-I) data

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Recent Results from Super-Kamiokande on Atmospheric Neutrino Measurements

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  1. Recent Results from Super-Kamiokande on Atmospheric Neutrino Measurements Choji SajiICRR,Univ. of Tokyofor the Super-Kamiokande collaboration ICHEP 2004, Beijing Contents • Atmospheric neutrino oscillation studies using full Super-Kamiokande I(SK-I) data • nm  nt oscillation analysis • L/E analysis • 3-flavor analysis • StatusofSuper-Kamiokande II(SK-II)

  2. Zenith angle p, He … , K  Flux(m-2sec-1sr-1GeV-1)   Zenith angle dist. of Atmospheric n flux Atmospheric neutrinos  Downward （L=10~100 km） e± e Upward （L=up to 13000 km） cosq En > a few GeV Up/Down Symmetry

  3. Event classification n energy distribution Fully Contained (E ~1GeV) Partially Contained (E ~10GeV) Stopping (E~10GeV) Through-going (E~100GeV) Atmospheric neutrinos in Super-Kamiokande

  4. 2-flavor oscillation analysis Data set: full SK-I (FC,PC 1489days, up- 1646 days) Improvements: • Expectation - Three dimensional (3D) n flux calculation -  interaction parameters (tuned by K2K data) • Treatment of systematic errors in c2 calculation • Each systematic error source is treated as independent error term(39 error terms)

  5. Zenith angle distributions    2-flavor oscillations Best fitsin22q=1.0, Dm2=2.1x10-3 eV2 Null oscillation ~13000km ~500km ~15km ~13000km ~500km

  6.  2-flavor oscillations Oscillation Analysis Results (FC + PC + UP-m) 10-3 10-2 • Best fit: sin22 =1.0 m2 = 2.1x10-3 eV2 2 = 175.2/177 dof • 90% C.L. region: sin22 > 0.92 1.5 < m2 < 3.4x10-3 eV2 0.7 0.75 0.8 0.85 0.9 0.95 1 Full paper will be soon

  7. Oscillation Decay Decoherence L/E Analysis A first dip should be observed • Direct evidence for oscillations • Strong constraint to oscillation parameters, especially Dm2 value FC single-ring 1/2 oscillation Full oscillation • Expand fiducial volume(FC) • need more statistics • Select events with highresolution in L/E • DL/E < 70% • FC(single, multi-ring) m-like • PC D(L/E)=70%

  8. L/E Distribution Mostly upward 1489.2 days FC+PC Best fit expectation w/ systematic errors Null oscillation MC Mostly downward First dip is seen as expected by neutrino oscillation

  9. Oscillation Decay Decoherence L/E Significance Dc2 (n decay –n oscillation) =11.4 3.4 s Dc2 (n decoherence -n oscillation)=14.6 3.8 s The first dip of the data cannot be explained by other models

  10. standard zenith angle analysis(90%C.L.) L/E Oscillation result Dm2=2.4x10-3,sin22q=1.00 c2min=37.9/40 d.o.f (sin22q=1.02, c2min=37.7/40 d.o.f) 1.9x10-3 < Dm2 < 3.0x10-3 eV2 0.90 < sin22q@ 90% C.L. Strong constraint on Dm2

  11. m3 Dm223 m2 Dm212 m1 3-flavor Oscillation assuming Dm212 = 0　eV2 neutrino oscillation probabilities are described as; P(negnm) = sin2(2q13) x sin2q23 x sin2(1.27Dm2L/E) P(nmgnt) = cos4q13 x sin2(2q23) x sin2(1.27Dm2L/E) P(negne) = 1 - sin2(2q13)x sin2(1.27Dm2L/E) 3 parameters; Dm223= Dm213, q13, q23 Oscillation probability ( cosQ=-0.6) P(nene) matter effect log10(E(GeV))

  12. Dm2 sin2q13 3-Flavor Analysis result (preliminary) sin2q13 Dm2 m3 normal m2 m1 m2 m1 sin2q13 inverted m3 Bestfit: Dm2 = 2.7x10-3ev2, sin2q23 = 0.5, sin2q13 = 0.0 sin2q23 no evidence for non zero q13

  13. SK - II

  14. Status of SK-II Atmospheric Neutrinos Preliminary! SK-II event • 311.5days data (preliminary) • SK-II data are consistent with SK-I • Clear deficit in upward nm

  15. Conclusion SK-I analysis  oscillation • SK-I full data set (FC,PC 1489days, up- 1646days) • Improved MC prediction and oscillation analysis •  allowed region @ 90% C.L. 1.5 < m2 < 3.4x10-3 eV2, sin22 > 0.92 • SK-I final result will be published soon L/E analysis • Evidence for oscillatory signature1.9 < Dm2 < 3.0x10-3 eV2, sin22q > 0.90@90%C.L. 3 - flavor oscillation - no evidence for non zero q13 SK-II analysis is in progress -preliminary data are consistent with SK-I

  16. Supplements

  17. CPT VIOLATION

  18. 2-flavor

  19. Definition of 2 2-flavor Calculation methods, basic idea (based on Fogli et al., hep-ph/0206162) In our current analysis, minimum χ2 is obtained by optimizing εj (j = 1,2,..) for each (sin22θ,Δm2) point. But, mathematically, χ2 is minimum ⇔ for any j . Minimizing χ2 ⇔ Solving nsys linear equation.

  20. Sub-Sample Consistency 2-flavor Check oscillation fit using different samples of data independently each allowed region overlaps with best fit point

  21. L/E Reconstruction of E and L Neutrino energy Neutrino direction FC single-ring En Preliminary 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

  22. L/E Event samples in L/E analysis 1.5m from top & bottom FC single-ring, multi-ring m-like 22.5kt →26.4kt Expand fiducial volume 1m from barrel More statistics for high energy muons observed charge / expectation from through-going PC Classify PC events using OD charge OD stopping OD through-going • OD stopping • OD through going OD through-going MC Different L/E resolution OD stopping MC

  23. Sensitivities to alternative models n decoherence obtained Dc2 Consistent with the expectation n decay Assumption nm nt 2 flavor oscillation (Dm2=2.0x10-3eV2,sin22q=1.0) L/E resolution cut at 70%

  24. L/E Definition of c2 Poisson with systematic errors Nobs : observed number of events Nexp : expectation from MC ei : systematic error term si: sigma of systematic error Various systematic effects in detector, flux calculation and neutrino interaction are taken into account

  25. 3-flavor Real Dm2 =positive assumed P(nmne) cosQ En(GeV) (No resonance for anti-neutrinos)

  26. c2 definition for 3-flavor analysis analytic calculation of Mij x ej = vi

  27. CC ne CC ne 3-flavor Single-ring e-like Multi-ring e-like NC + Others NC +Others CC ne CC ne

  28. 20inch PMT with Acrylic + FRP vessel SK-II SK-II partially-contained sample • Rebuilt in summer 2002 • Has 47% of original ID 20inch PMTs (~5200) • 20inch PMTs in acrylic shells to prevent future chain implosions • Has full OD 8inch PMTs (1885) • Started data taking inDec. 2002

  29. SK2 Number of Events / Event rate in fiducial volume Number of Events (Event rate, Ev/day)

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