Neutrino oscillation physics potential of the T2K experiment

The observation of the recent electron neutrino appearance in a muon neutrino beam and the high-precision measurement of the mixing angle $\theta _{13}$ have led to a re-evaluation of the physics potential of the T2K long-baseline neutrino oscillation experiment. Sensitivities are explored for CP violation in neutrinos, non-maximal $\sin ^22\theta _{23}$, the octant of $\theta _{23}$, and the mass hierarchy, in addition to the measurements of $\delta _{{\rm CP}}$, $\sin ^2\theta _{23}$, and $\Delta m^2_{32}$, for various combinations of $\nu$-mode and $\bar {\nu }$-mode data-taking.With an exposure of $7.8\times 10^{21}$ protons-on-target, T2K can achieve 1$\sigma$ resolution of 0.050 (0.054) on $\sin ^2\theta _{23}$ and $0.040\ (0.045)\times 10^{-3}\,\rm {eV}^2$ on $\Delta m^2_{32}$ for 100% (50%) neutrino beam mode running assuming $\sin ^2\theta _{23}=0.5$ and $\Delta m^2_{32} = 2.4\times 10^{-3}\,\hbox {eV}^2$. T2K will have sensitivity to the CP-violating phase $\delta _{\rm {CP}}$ at 90% C.L. or better over a significant range. For example, if $\sin ^22\theta _{23}$ is maximal (i.e. $\theta _{23}=45^\circ$) the range is $-115^\circ \lt \delta _{\rm {CP}}\lt -60^\circ$ for normal hierarchy and $+50^\circ \lt \delta _{\rm {CP}}\lt +130^\circ$ for inverted hierarchy. When T2K data is combined with data from the NO$\nu$A experiment, the region of oscillation parameter space where there is sensitivity to observe a non-zero $\delta _{{\rm CP}}$ is substantially increased compared to if each experiment is analyzed alone.