1. 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)

2. 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 

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

4. 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:

5. 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

6. 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

7. 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

8. 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

9. 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 

10. 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.)

11. 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)

12. 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 m2m2 m2m2 (preliminary)

13. SK - II

14. 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 

15. 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