arXiv subjects
Publications and source records attributed to Osamu Yasuda.
Superkamiokande atmospheric neutrino data for 990 days are analyzed in the framework of four neutrinos without imposing constraints of Big Bang Nucleosynthesis. It is shown that the wide range of the oscillation parameters is allowed at 90% confidence level ($0.1\lsim |U_{s1}|^2+|U_{s2}|^2\le 1$).
Superkamiokande atmospheric neutrino data (contained and upward going through $μ$ events) for 990 days are analyzed in the framework of four neutrinos (three active and one sterile neutrinos) without imposing constraints of Big Bang Nucleosynthesis. It is shown that the wide range of the oscillation parameters is allowed at 90% confidence level ($0.1\lesssim |U_{s1}|^2+|U_{s2}|^2\le 1$), where the best fit point has some contribution of $ν_μ\leftrightarrowν_s$ and contribution of $Δm^2_{\rm\scriptsize LSND}$. The case of pure $ν_μ\leftrightarrowν_s$ oscillation is excluded at 99.7%CL (3.0$σ$) which is consistent with the recent analysis by the Superkamiokande group. Combining this result with the analysis by Giunti, Gonzarez-Garcia and Peña-Garay, it is found that the Large Mixing Angle and Vacuum Oscillation solutions of the solar neutrino problem are also allowed.
I discuss the effects of neutrino oscillations on high energy cosmic neutrinos which come from cosmologically distant astrophysical sources. I incorporate all the up-to-date constraints from the solar, atmospheric, reactor, accelerator data and give the possible pattern for the ratio of the high energy cosmic neutrinos in the cases of three and four neutrino schemes.
It is shown in the three flavor framework that neutrino factories enable us to measure some of the oscillation parameters, such as the sign of $Δm_{32}^2$, $θ_{13}$, $δ$. Some efforts are made to determine the parameters (the muon energy and the neutrino path length) of a neutrino factory to optimize the signals.
Using the result of the three flavor analysis of the old Kamiokande data, the recent Superkamiokande data of atmospheric neutrinos and the CHOOZ reactor data, it is shown that the third mixing angle $θ_{13}$ is small. It is proposed to determine the small value of $θ_{13}$ and the CP violating phase $δ$ in very long baseline experiments by measuring the appearance probability $P(ν_μ\toν_e)$ and the T violating effect $P(ν_e\toν_μ)-P(ν_μ\toν_e)$ which are enhanced by the matter effect of the Earth.
Superkamiokande atmospheric neutrino data for 414 days are analyzed in the framework of three flavor oscillations with mass hierarchy. It is shown that the best fit point is very close to the pure maximal $ν_μ\leftrightarrowν_τ$ case and $Δm^2 \simeq 7\times10^{-3}$ eV$^2$. The allowed region at 90 %CL is given and the implications to the long baseline experiments are briefly discussed. It is also shown that the threefold maximal mixing model fits to the data of atmospheric neutrinos and the reactor experiments for $Δm^2 \sim 1\times10^{-3}$ eV$^2$.
The $ν_μ\leftrightarrowν_τ$ and $ν_μ\leftrightarrowν_s$ solutions to the atmospheric neutrino problem are compared with Superkamiokande data. Both the solutions with a large mixing angle seem to be consistent with the data.
Superkamiokande atmospheric neutrino data for 535 days are analyzed in the framework of three flavor oscillations with mass hierarchy. It is shown that the best fit point is very close to the pure maximal $ν_μ\leftrightarrowν_τ$ case and $Δm^2 \simeq 7\times10^{-3}$ eV$^2$. The allowed region at 90 %CL is given and the implications to the long baseline experiments are briefly discussed.
It has been known that there are two schemes in the framework of three flavor neutrinos to accommodate the global features of the hot dark matter neutrinos, the solar neutrino deficit and the atmospheric neutrino anomaly in a manner consistent with terrestrial neutrino experiments, i.e., hierarchical mass neutrinos and almost degenerate neutrinos. We demonstrate that the recent result by the CHOOZ experiment excludes the scheme of hierarchical neutrinos. We also point out in the scheme of almost degenerate neutrinos that if neutrinos are Majorana particles then the double $β$ decay experiments must see positive signals on their way to reach a limit more stringent than the present one by a factor of 5.
Using the published Kamiokande binned data for sub-GeV and multi-GeV atmospheric neutrinos, we have searched for the optimum set of three flavor neutrino oscillation parameters within the constraints of reactor experiments. It is found that chi^2 is minimized for (Delta m_{21}^2, Delta m_{32}^2, theta_{12}, theta_{13}, theta_{23}) = (7.4x10^{-1} eV^2, 2.6x 10^{-2} eV^2, 2 deg, 3 deg, 45 deg) and (2.6x 10^{-2} eV^2, 7.4x10^{-1} eV^2, 0 deg, 87 deg, 46 deg) with chi_{min}^2 = 87.8 (76%CL). The sets of parameters which are suggested by the two flavor analysis turn out to be close to the minimum (0.2sigma).
We discuss constraints on a scenario of almost degenerate three-flavor neutrinos imposed by the solar and the atmospheric neutrino anomalies, hot dark matter, and neutrinoless double $β$ decays. It is found that in the Majorana version of the model the region with relatively large $θ_{13}$ is favored and a constraint on the CP violating phases is obtained.
We discuss a model in which three active and one sterile neutrino account for the solar, the atmospheric and the LSND neutrino anomalies. It is shown that if $N_ν<4$ then these and other experiments and big bang nucleosynthesis constrain all the mixing angles severely, and allow only the small-angle MSW solution. If these neutrinos are of Majorana type, then negative results of neutrinoless double beta decay experiments imply that the total mass of neutrinos is not sufficient to account for all the hot dark matter components.
We discuss constraints on three flavor neutrino mixings from the accelerator and reactor experiments, the Kamiokande multi-GeV data, and the solar neutrino observations. The LSND result is excluded at 90\%CL by the constraints imposed by all the data of reactor and accelerator experiments and the Kamiokande multi-GeV data if the mass scale required for the solution to the solar neutrino problem is hierarchically small. The region of a set of the effective two-flavor mixing parameters ($Δm^2$, $\sin^22θ$) is given for the channel $ν_μ\rightarrowν_e$ which is allowed at 90\%CL by the multi-GeV Kamiokande data alone.
Using the published Kamiokande data of the multi-GeV atmospheric neutrinos, we have searched the optimum set of the neutrino oscillation parameters among three flavors. It is found that $χ^2$ is minimized for ($Δm_{21}^2$, $Δm_{31}^2$) = (3.8$\times 10^{-2}~$eV$^2$, 1.4$\times 10^{-2}~$eV$^2$), ($θ_{12}$, $θ_{13}$, $θ_{23}$) = ($19^\circ$,$43^\circ$,$41^\circ$) with $χ_{\rm min}$ = 3.2 (42\%CL). The sets of parameters ($Δm_{21}^2$, $Δm_{31}^2$) = (${\cal O}$($10^{-11}$eV$^2$) or ${\cal O}$($10^{-5}$eV$^2$), ${\cal O}$($10^{-2}$eV$^2$)) which are suggested by the two flavor analysis fall within 0.7$σ$.
Possible breakdown of the universality of the gravitational couplings to different neutrino flavors can be tested in long-baseline neutrino-oscillation experiments, such as a proposed experiment at SOUDAN 2 or one at the DUMAND project. Such a breakdown could be detected with sensitivity to the order of $10^{-14}$ or $10^{-15}$. For generic case of neutrino oscillations, it is emphasized that one can identify the spin of the particle which mediates the force causing the oscillation, by investigating the energy spectrum of the outgoing charged leptons. (based on talk presented at the Workshop on General Relativity and Gravitation held at Univ. of Tokyo, January 17-20, 1994)
We show that a breakdown of the universality of the gravitational couplings to different neutrino flavors can be tested in long-baseline neutrino-oscillation experiments. In particular we have analyzed in detail a proposed experiment at SOUDAN 2 with $ν_μ$ beams from the Fermilab Main Injector. It turns out that we can study both masses of neutrinos and such a breakdown with sensitivity to the order of $10^{-14}$ by investigating the energy spectrum of the resulting muons.