arXiv subjects
Publications and source records attributed to Yuichi Oyama.
The atmospheric muon neutrino deficit, which was possible evidence of $ν_μ\leftrightarrow ν_τ$ oscillation, was reported by the Kamiokande experiment from 1988. Many experimental efforts were made to examine the Kamiokande results. Experiments which contributed to the confirmation of $ν_μ\leftrightarrow ν_τ$ oscillation are reviewed. Especially, long-baseline neutrino-oscillation experiments are described in detail.
The seven seconds' gap in the Kamiokande-II SN1987A neutrino data is reexamined.
High-energy neutrinos from SN1987A were searched for using upward-going muons recorded by the Kamiokande-II experiment and the IMB experiment. Between 1987 August 11 and October 20, and from an angular window of 10 degree radius, two upward-going muon events were recorded by Kamiokande-II, and also two events were recorded by IMB. The probability that these upward-going muons were explained by a chance coincidence of atmospheric neutrinos was calculated to be 0.27%. This shows possible evidence of high-energy neutrinos from SN1987A.
J-PARC neutrino beamline has been operated since 2009. Until May 2018, the maximum beam power achieved was ~500 kW. In future, the beam power will be upgraded to 1.3 MW. After the stable operation in late 2020s, we can accumulate ~30 x 10^20 POT data per year. It is almost the same number as total POT accumulated in recent 10 years. The upgrade plan of the Main Ring as well as the neutrino beamline is reported.
The T2K long-baseline neutrino-oscillation experiment accumulated approximately 11.0x10^20 POT (protons on target) data until June 2015. The results of ν_e appearance as well as ν_μdisappearance for 6.57x10^20 POT neutrino beam data are reported. A comparison with the results of reactor ν_e disappearance experiments provides possible hints toward negative δ_CP phase with normal mass hierarchy. Preliminary results based on 4.04x10^20 POT anti-neutrino beam data are also presented.
The T2K long-baseline neutrino-oscillationexperiment was started in January 2010 for the purpose of physics data-taking. Until the massive earthquake on March 11, 2011 in Japan, $1.43\times 10^{20}$ pot data were accumulated. In this data, 6 possible $ν_{e}$ appearance candidates are found forexpected background of 1.5$\pm$0.3(syst.)if $\sin^{2}2θ_{13}=0$ is assumed.The probability that 6 or more events can be observed for1.5$\pm$0.3 expected events is 7$\times10^{-3}$,equivalent to 2.5$σ$ significance. This is the first indication of a $ν_{e}$ appearance or, in other words, the first indication of a non-zero $\sin^{2}2θ_{13}$.
A first-ever 2-dimensional celestial map of primary cosmic-ray flux was obtained from 2.10x10^8 cosmic-ray muons accumulated in 1662.0 days of Super-Kamiokande. The celestial map indicates an (0.104 \pm 0.020)% excess region in the constellation of Taurus and a -(0.094 \pm 0.014)% deficit region toward Virgo. Interpretations of this anisotropy are discussed.
Results from the K2K experiment and status of the T2K experiment are reported.
New results from the K2K (KEK to Kamioka) long-baseline neutrino-oscillation experiment is presented.
Current status of the K2K (KEK to Kamioka) long-baseline neutrino-oscillation experiment is presented.
New physics results from the Super-Kamiokande experiment in 2000 are presented.
The K2K (KEK to Kamioka) long-baseline neutrino-oscillation experiment was successfully started in early 1999. A total intensity of 7.20 x 10^18 protons on target, which is about 7% of the goal of the experiment, was accumulated in 39.4 days of data-taking in 1999. We obtained 3 neutrino events in the fiducial volume of the Super-Kamiokande detector, whereas the expectation based on observations in the front detectors is 12.3 +1.7/-1.9. An analysis of oscillation searches from the view points of absolute event numbers, distortion of neutrino energy spectrum, and nu_e/nu_mu ratio is in progress.
A long-baseline neutrino-oscillation experiment using a well-defined neutrino beam is in preparation at KEK. Neutrinos generated at KEK will be detected by the Super-kamiokande detector 250 km away. The design of the neutrino beam line, beam monitors and detector are briefly presented. The sensitivities for neutrino oscillations are also discussed.