We report measurements by the T2K experiment of the parameters
θ
23
and
Δ
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
×
1
0
20
POT in neutrino running mode and
7.471
×
1
0
20
POT in antineutrino mode, T2K obtained
sin
2
(
θ
23
)
=
0.5
1
+
0.08
−
0.07
and
Δ
m
2
32
=
2.5
3
+
0.15
−
0.13
×
10
−
3
 
 
eV
2
/
c
4
for neutrinos, and
sin
2
(
¯
θ
23
)
=
0.4
2
+
0.25
−
0.07
and
Δ
¯
m
2
32
=
2.5
5
+
0.33
−
0.27
×
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.