Have Superkamiokande Really Measured the Direction of the Atmospheric Neutrinos which Produce Fully Contained Events and Partially Contained Events ?

摘要

Quasi Elastic Scattering (QEL) is the dominant source for producing bothFully Contained Events and Partially Contained Events in theSuperkamiokande(SK) detector for the atmospheric neutrinos, in the range 0.1GeV to 10 GeV. In the analysis of SK events, it is assumed that the directionof the incident neutrino is the same as that of the detected charged lepton. Inthe present letter, we derive the distribution function for the scatteringangle of the charged leptons, their averaged scattering angle and theirstandard deviation due to QEL. Then, it is shown that the SK assumption for thescattering angle of the charged leptons in the QEL is not valid. Further, weexamine the influence of the azimuthal angle of the charged leptons over theirzenith angle. As the result, we conclude that the zenith angle distribution ofthe neutrino under the SK assumption does not reflect the real zenith angledistribution of the atmospheric neutrino which produces Fully Contained Eventsand Partially Contained Events. This result has clear implication for attemptsto detect neutrino oscillations from the analyses of Fully Contained Events andPartially Contained Events in Superkamiokande.