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Register a new userImproved constraints on neutrino mixing from the T2K experiment with $mathbf{3.13times10^{21}}$ protons on target
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The T2K experiment reports updated measurements of neutrino and antineutrino oscillations using both appearance and disappearance channels. This result comes from an exposure of $14.9~(16.4) times 10^{20}$ protons on target in neutrino (antineutrino) mode. Significant improvements have been made to the neutrino interaction model and far detector reconstruction. An extensive set of simulated data studies have also been performed to quantify the effect interaction model uncertainties have on the T2K oscillation parameter sensitivity. T2K performs multiple oscillation analyses that present both frequentist and Bayesian intervals for the PMNS parameters. For fits including a constraint on ssqthonethree from reactor data and assuming normal mass ordering T2K measures $sin^2theta_{23} = 0.53^{+0.03}_{-0.04}$ and $Delta{}m^2_{32} = (2.45 pm 0.07) times 10^{-3}$ eV$^{2}$c$^{-4}$. The Bayesian analyses show a weak preference for normal mass ordering (89% posterior probability) and the upper $sin^2theta_{23}$ octant (80% posterior probability), with a uniform prior probability assumed in both cases. The T2K data exclude CP conservation in neutrino oscillations at the $2sigma$ level.
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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 $Delta m^2_{32}=2.463^{+0.071}_{-0.070}times10^{-3} mathrm{eV}^2/c^4$.
We report measurements by the T2K experiment of the parameters $theta_{23}$ and $Delta m^2_{32}$ which govern the disappearance of muon neutrinos and antineutrinos in the three-flavor PMNS neutrino oscillation model at T2Ks neutrino energy and propagation distance. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, muon-like events from each beam mode are used to measure these parameters separately for neutrino and antineutrino oscillations. Data taken from $1.49 times 10^{21}$ protons on target (POT) in neutrino mode and $1.64 times 10^{21}$ POT in antineutrino mode are used. The best-fit values obtained by T2K were $sin^2left(theta_{23}right)=0.51^{+0.06}_{-0.07} left(0.43^{+0.21}_{-0.05}right)$ and $Delta m^2_{32}=2.47^{+0.08}_{-0.09} left(2.50^{+0.18}_{-0.13}right)$evmass for neutrinos (antineutrinos). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed. An analysis using an effective two-flavor neutrino oscillation model where the sine of the mixing angle is allowed to take non-physical values larger than 1 is also performed to check the consistency of our data with the three-flavor model. Our data were found to be consistent with a physical value for the mixing angle.
We report on measurements of neutrino oscillation using data from the T2K long-baseline neutrino experiment collected between 2010 and 2013. In an analysis of muon neutrino disappearance alone, we find the following estimates and 68% confidence intervals for the two possible mass hierarchies: Normal Hierarchy: $sin^2theta_{23}=0.514^{+0.055}_{-0.056}$ and $Delta m^2_{32}=(2.51pm0.10)times 10^{-3}$ eV$^2$/c$^4$ Inverted Hierarchy: $sin^2theta_{23}=0.511pm0.055$ and $Delta m^2_{13}=(2.48pm0.10)times 10^{-3}$ eV$^2$/c$^4$ The analysis accounts for multi-nucleon mechanisms in neutrino interactions which were found to introduce negligible bias. We describe our first analyses that combine measurements of muon neutrino disappearance and electron neutrino appearance to estimate four oscillation parameters and the mass hierarchy. Frequentist and Bayesian intervals are presented for combinations of these parameters, with and without including recent reactor measurements. At 90% confidence level and including reactor measurements, we exclude the region: $delta_{CP}=[0.15,0.83]pi$ for normal hierarchy and $delta_{CP}=[-0.08,1.09]pi$ for inverted hierarchy. The T2K and reactor data weakly favor the normal hierarchy with a Bayes Factor of 2.2. The most probable values and 68% 1D credible intervals for the other oscillation parameters, when reactor data are included, are: $sin^2theta_{23}=0.528^{+0.055}_{-0.038}$ and $|Delta m^2_{32}|=(2.51pm0.11)times 10^{-3}$ eV$^2$/c$^4$.
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.
The STEREO experiment is a very short baseline reactor antineutrino experiment. It is designed to test the hypothesis of light sterile neutrinos being the cause of a deficit of the observed antineutrino interaction rate at short baselines with respect to the predicted rate, known as the reactor antineutrino anomaly. The STEREO experiment measures the antineutrino energy spectrum in six identical detector cells covering baselines between 9 and 11 m from the compact core of the ILL research reactor. In this article, results from 179 days of reactor turned on and 235 days of reactor turned off are reported at a high degree of detail. The current results include improvements in the modelling of detector optical properties and the gamma-cascade after neutron captures by gadolinium, the treatment of backgrounds, and the statistical method of the oscillation analysis. Using a direct comparison between antineutrino spectra of all cells, largely independent of any flux prediction, we find the data compatible with the null oscillation hypothesis. The best-fit point of the reactor antineutrino anomaly is rejected at more than 99.9% C.L.
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