Recent results on atomospheric neutrino oscillation from Super-Kamiokande

Abstract

Super-Kamiokande is a large water Cerenkov detector which consists of 50 kton pure water as a target of observation of atmospheric, solar, supernovae and accelerator neutrino and as a source of nucleon decay. Cherenkov lights emitted by charged particles from neutrino interaction at 22.5 kton of ducial volume are viewed by 11,146 inward-facing 20-inch photomultiplier tubes(PMTs) during the rst run of the detector, SK-I. The two subsequent run periods, SK-II and SK-III had 5,182 and 11,129 PMTs respectively. The outer detector surrounding the inner volume has been instrumented with 1,885 outward-facing 8-inch PMTs and used primarily as a veto. Although Super-Kamiokande has provided enormous amount of data and physics results [1] for more than 10 years since the observation started in 1996, DAQ electronics and computers are upgraded in September 2008. There are several motivations from physics to upgrade the electronics and online system. A wider charge dynamic range enables us improvement of energy resolution of high energy atmospheric neutrino events. A trigger window with much longer time enables us to improve muon decay electron nding ef ciency in atmospheric neutrino study and nucleon decay search. After the commissioning of new DAQ system, intensive calibration works have been performed, then, SK started its physics data taking as SK-IV in October 2008. In the paper, atmospheric neutrino oscillation analysis results from SK-I+II+III (before electronics upgrade) data on standard 2avor oscillation, 3avor oscillation with normal and inverted hierarchy, and search for CPT violation, and Early data of atmospheric neutrino from SK-IV are reported.