Constraints on Oscillation Parameters from ${\nu }_e$ Appearance and ${\nu }_{\mu }$ Disappearance in NOvA

Results are reported from an improved measurement of ${\nu }_{\mu }\to {\nu }_e$ transitions by the NOvA experiment. Using an exposure equivalent to $6.05\times 10^{20}$ protons on target, 33 ${\nu }_e$ candidates are observed with a background of $8.2\pm 0.8$ (syst.). Combined with the latest NOvA ${\nu }_{\mu }$ disappearance data and external constraints from reactor experiments on ${\sin }^{2}2{\theta }_{13}$, the hypothesis of inverted mass hierarchy with ${\theta }_{23}$ in the lower octant is disfavored at greater than 93% C.L. for all values of ${\delta }_{CP}$.

Figure 1

Reconstructed energy of events selected in the ND data and simulation by the ${\nu }_e$ CC selection criteria in the three ${\nu }_e$ classifier (CVN) bins. The leftmost panel is the lowest purity classifier bin, while the rightmost has the highest purity.

Figure 2

Total number of selected ${\nu }_e$ candidate events expected at the FD. The blue represents NH and the orange IH. The bands correspond to the range ${\sin }^2{\theta }_{23}=0.40$ (lower edge) to 0.62 (upper edge), with the solid line marking the maximal mixing. The $x$ axis gives the value of the $CP$ phase, while all other parameters are held fixed at the best-fit values found by NOvA’s latest analysis of ${\nu }_{\mu }$ disappearance [30].

Figure 3

Reconstructed energy of selected FD events in three bins of the CVN classifier variable. Black points show the data, and the red line shows the predicted spectrum at the best-fit point in NH, with the blue area showing the total expected background.

Figure 4

Regions of ${\delta }_{CP}$ vs ${\sin }^2{\theta }_{23}$ parameter space consistent with the observed spectrum of ${\nu }_e$ candidates and the ${\nu }_{\mu }$ disappearance data [30]. The top panel corresponds to normal mass hierarchy ($\mathrm{\Delta }{m}_{32}^2>0$) and the bottom panel to inverted hierarchy ($\mathrm{\Delta }{m}_{32}^2<0$). The color intensity indicates the confidence level at which particular parameter combinations are allowed.

Figure 5

Feldman-Cousins corrected significance at which each value of ${\delta }_{CP}$ is disfavored for each of the four possible combinations of mass hierarchy [normal (blue curves) or inverted (red curves)] and ${\theta }_{23}$ octant [lower (solid curves) or upper (dashed curves)] by the combination of ${\nu }_e$ appearance and NOvA’s latest ${\nu }_{\mu }$ disappearance measurement [30].