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T2K reports its first results in the search for CP violation in neutrino oscillations using appearance and disappearance channels for neutrino- and antineutrino-mode beam. The data include all runs from Jan 2010 to May 2016 and comprise $7.482times10^{20}$,protons on target in neutrino mode, which yielded in the far detector 32 e-like and 135 $mu$-like events, and $7.471times10^{20}$,protons on target in antineutrino mode which yielded 4 e-like and 66 $mu$-like events. Reactor measurements of $sin^{2}2theta_{13}$ have been used as an additional constraint. The one-dimensional confidence interval at 90% for $delta_{CP}$ spans the range ($-3.13$, $-0.39$) for normal mass ordering. The CP conservation hypothesis ($delta_{CP}=0,pi$) is excluded at 90% C.L.
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This paper presents the first combined measurement of the double-differential muon neutrino and antineutrino charged-current cross sections with no pions in the final state on hydrocarbon at the off-axis near detector of the T2K experiment. The data analyzed in this work comprise 5.8$times$10$^{20}$ and 6.3$times$10$^{20}$ protons on target in neutrino and antineutrino mode respectively, at a beam energy peak of 0.6 GeV. Using the two measured cross sections, the sum, difference and asymmetry were calculated with the aim of better understanding the nuclear effects involved in such interactions. The extracted measurements have been compared with the prediction from different Monte Carlo generators and theoretical models showing that the difference between the two cross sections have interesting sensitivity to nuclear effects.
The T2K experiment reports an updated analysis of neutrino and antineutrino oscillations in appearance and disappearance channels. A sample of electron neutrino candidates at Super-Kamiokande in which a pion decay has been tagged is added to the four single-ring samples used in previous T2K oscillation analyses. Through combined analyses of these five samples, simultaneous measurements of four oscillation parameters, $|Delta m^2_{32}|$, $sin^2(theta_{23})$, $sin^2(theta_{13})$, and $delta_{CP}$ and of the mass ordering are made. A set of studies of simulated data indicates that the sensitivity to the oscillation parameters is not limited by neutrino interaction model uncertainty. Multiple oscillation analyses are performed, and frequentist and Bayesian intervals are presented for combinations of the oscillation parameters with and without the inclusion of reactor constraints on $sin^2(theta_{13})$. When combined with reactor measurements, the hypothesis of CP conservation ($delta_{CP}$$=0$ or $pi$) is excluded at 90% confidence level. The 90% confidence region for $delta_{CP}$ is [-2.95,-0.44] ([-1.47, -1.27]) for normal (inverted) ordering. The central values and 68% confidence intervals for the other oscillation parameters for normal (inverted) ordering are $Delta m^{2}_{32}=2.54pm0.08$ ($2.51pm0.08$) $times 10^{-3}$ eV$^2 / c^4$ and $sin^2(theta_{23}) = 0.55^{+0.05}_{-0.09}$ ($0.55^{+0.05}_{-0.08}$), compatible with maximal mixing. In the Bayesian analysis, the data weakly prefer normal ordering (Bayes factor 3.7) and the upper octant for $sin^2(theta_{23})$ (Bayes factor 2.4).
The T2K experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and antineutrino beams. With an exposure of $14.7(7.6)times 10^{20}$ protons on target in neutrino (antineutrino) mode, 89 $ u_e$ candidates and 7 anti-$ u_e$ candidates were observed while 67.5 and 9.0 are expected for $delta_{CP}=0$ and normal mass ordering. The obtained $2sigma$ confidence interval for the $CP$ violating phase, $delta_{CP}$, does not include the $CP$-conserving cases ($delta_{CP}=0,pi$). The best-fit values of other parameters are $sin^2theta_{23} = 0.526^{+0.032}_{-0.036}$ and $Delta m^2_{32}=2.463^{+0.071}_{-0.070}times10^{-3} mathrm{eV}^2/c^4$.
The KARMEN experiment at the spallation neutron source ISIS used umub from mup--decay at rest in the search for neutrino oscillations umubnueb in the appearance mode, with p( ueb,e+)n as detection reaction of ueb. In total, 15 candidates fulfill all conditions for the ueb signature, in agreement with the background expectation of 15.8+-0.5 events, yielding no indication for oscillations. A single event based likelihood analysis leads to upper limits on the oscillation parameters: sin^2(2theta)<1.7x10e-3 for Dm^2>100 eV^2 and Dm^2<0.055 eV^2 for sin^2(2theta)=1 at 90% confidence. Thus, KARMEN does not confirm the LSND experiment and restricts significantly its favored parameter region for umubnueb.
We report measurements by the T2K experiment of the parameters $theta_{23}$ and $Delta m^{2}_{32}$ governing the disappearance of muon neutrinos and antineutrinos in the three flavor neutrino oscillation model. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, the parameters are measured separately for neutrinos and antineutrinos. Using $7.482 times 10^{20}$ POT in neutrino running mode and $7.471 times 10^{20}$ POT in antineutrino mode, T2K obtained, $sin^{2}(theta_{23})=0.51^{+0.08}_{-0.07}$ and $Delta m^{2}_{32} = 2.53^{+0.15}_{-0.13} times 10^{-3}$eV$^{2}$/c$^{4}$ for neutrinos, and $sin^{2}({overline{theta}}_{23})=0.42^{+0.25}_{-0.07}$ and ${Deltaoverline{m}^2}_{32} = 2.55^{+0.33}_{-0.27} times 10^{-3}$eV$^{2}$/c$^{4}$ for antineutrinos (assuming normal mass ordering). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed.
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