Abstract
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 T2K's 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 $\sin^2\left(\theta_{23}\right)=0.51^{+0.06}_{-0.07} \left(0.43^{+0.21}_{-0.05}\right)$ 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.
Highlights
We present an update of T2K’s νμ and νμ disappearance measurement from Ref. [1] with a larger statistical sample and significant analysis improvements
No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed
We report measurements by the T2K experiment of the parameters θ23 and Δm232, which govern the disappearance of muon neutrinos and antineutrinos in the three-flavor PMNS neutrino oscillation model at T2K’s neutrino energy and propagation distance
Summary
We present an update of T2K’s νμ and νμ disappearance measurement from Ref. [1] with a larger statistical sample and significant analysis improvements. § at National Research Nuclear University “MEPhI” and Moscow Institute of Physics and Technology, Moscow, Russia. To test consistency with the PMNS formalism, we present an analysis in which the oscillation probability is allowed to exceed the maximum possible PMNS value In this analysis, for computational simplicity we approximate the probability for muon neutrino disappearance using a “two-flavor”-only oscillation formula with an effective mixing angle and mass splitting that takes into account the information we know about “three-flavor” mixing. Sin[2] ð2θÞ is allowed to take values exceeding 1, where θ is the effective neutrino mixing angle in this framework This two-flavor approximation gives probabilities that agree within better than 0.5% with the full PMNS calculation across T2K’s neutrino energy range at the best-fit parameter values from T2K’s joint muon and electron-like event analysis [2]
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