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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 – oscillation analysis – L/E analysis – 3-flavor analysis Status of Super-Kamiokande II(SK-II)

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

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

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

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Zenith angle distributions ~15km ~13000km~500km ~13000km ~500km 2-flavor oscillations Best fit sin 2 2 =1.0, m 2 =2.1x10 -3 eV 2 Null oscillation

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Oscillation Analysis Results ● Best fit: sin 2 2 =1.0 m 2 = 2.1x10 -3 eV 2 2 = 175.2/177 dof ● 90% C.L. region: sin 2 2 > 0.92 1.5 < m 2 < 3.4x10 -3 eV 2 2-flavor oscillations (FC + PC + UP- ) Full paper will be soon 0.70.80.910.750.850.95 10 -3 10 -2

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

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

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L/E Significance Oscillation Decay Decoherence The first dip of the data cannot be explained by other models 2 ( decay – oscillation) =11.4 3.4 2 ( decoherence - oscillation) =14.6 3.8

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L/E Oscillation result m 2 =2.4x10 -3,sin 2 2 =1.00 2 min =37.9/40 d.o.f (sin 2 2 =1.02, 2 min =37.7/40 d.o.f) 1.9x10 -3 < m 2 < 3.0x10 -3 eV 2 0.90 < sin 2 2 @ 90% C.L. Strong constraint on m 2 standard zenith angle analysis(90%C.L.)

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3-flavor Oscillation P( e ) = sin 2 (2 13 ) x sin 2 23 x sin 2 (1.27 m 2 L/E) P( ) = cos 4 13 x sin 2 (2 23 ) x sin 2 (1.27 m 2 L/E) P( e e ) = 1 - sin 2 (2 13 ) x sin 2 (1.27 m 2 L/E) assuming m 2 12 = 0 eV 2 3 parameters; m 2 23 = m 2 13, , 23 neutrino oscillation probabilities are described as; m3m3 m2m2 m1m1 m 2 23 m 2 12 Oscillation probability matter effect log10(E(GeV)) P( e e) ( cos =-0.6)

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3-Flavor Analysis result normal inverted Bestfit: m 2 = 2.7x10 -3 ev 2, sin 2 23 = 0.5, sin 2 13 = 0.0 no evidence for non zero 13 m3m3 m2m2 m1m1 m3m3 m2m2 m1m1 sin 2 23 sin 2 13 m2m2 m2m2 (preliminary)

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SK - II

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

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Conclusion SK-II analysis is in progress - preliminary data are consistent with SK-I oscillation – SK-I full data set (FC,PC 1489days, up- 1646days) – Improved MC prediction and oscillation analysis – allowed region @ 90% C.L. 1.5 0.92 – SK-I final result will be published soon L/E analysis – Evidence for oscillatory signature 1.9 0.90@90%C.L. 3 - flavor oscillation - no evidence for non zero 13 SK-I analysis

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