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 ${ \Delta\overline{ m}^2}_{ 32} = 2.55^{ +0.33}_{ -0.27} \times 10^{ -3}$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.
Categories: hep-ex