The NOvA experiment has seen a
4.4
σ
signal of
¯
ν
e
appearance in a 2 GeV
¯
ν
μ
beam at a distance of 810 km. Using
12.33
×
10
20
protons on target delivered to the Fermilab NuMI neutrino beamline, the experiment recorded 27
¯
ν
μ
→
¯
ν
e
candidates with a background of 10.3 and 102
¯
ν
μ
→
¯
ν
μ
candidates. This new antineutrino data are combined with neutrino data to measure the parameters
|
Δ
m
2
32
|
=
2.4
8
+
0.11
−
0.06
×
10
−
3
eV
2
/
c
4
and
sin
2
θ
23
in the ranges from (0.53–0.60) and (0.45–0.48) in the normal neutrino mass hierarchy. The data exclude most values near
δ
C
P
=
π
/
2
for the inverted mass hierarchy by more than
3
σ
and favor the normal neutrino mass hierarchy by
1.9
σ
and
θ
23
values in the upper octant by
1.6
σ
