An Improved Measurement of Neutrino Oscillation Parameters by the NOvA Experiment

Abstract: We present new $\nu_\mu\rightarrow\nu_e$, $\nu_\mu\rightarrow\nu_\mu$, $\overline{\nu}\mu\rightarrow\overline{\nu}_e$, and $\overline{\nu}\mu\rightarrow\overline{\nu}\mu$ oscillation measurements by the NOvA experiment, with a 50% increase in neutrino-mode beam exposure over the previously reported results. The additional data, combined with previously published neutrino and antineutrino data, are all analyzed using improved techniques and simulations. A joint fit to the $\nu_e$, $\nu\mu$, $\overline{\nu}e$, and $\overline{\nu}\mu$ candidate samples within the 3-flavor neutrino oscillation framework continues to yield a best-fit point in the normal mass ordering and the upper octant of the $\theta_{23}$ mixing angle, with $\Delta m^{2}_{32} = (2.41\pm0.07)\times 10^{-3}$ eV$^2$ and $\sin^2\theta_{23} = 0.57^{+0.03}_{-0.04}$. The data disfavor combinations of oscillation parameters that give rise to a large asymmetry in the rates of $\nu_e$ and $\overline{\nu}e$ appearance. This includes values of the CP-violating phase in the vicinity of $\delta\text{CP} = \pi/2$ which are excluded by $>3\sigma$ for the inverted mass ordering, and values around $\delta_\text{CP} = 3\pi/2$ in the normal ordering which are disfavored at 2$\sigma$ confidence.