  We present the first combined measurement of the rapidity and transverse
momentum dependence of dijet azimuthal decorrelations, based on the recently
proposed quantity $R_{\Delta \phi}$. The variable $R_{\Delta \phi}$ measures
the fraction of the inclusive dijet events in which the azimuthal separation of
the two jets with the highest transverse momenta is less than a specified value
for the parameter $\Delta \phi_{\rm max}$. The quantity $R_{\Delta \phi}$ is
measured in $p\bar{p}$ collisions at $\sqrt{s}=1.96\,$TeV, as a function of the
dijet rapidity interval, the total scalar transverse momentum, and $\Delta
\phi_{\rm max}$. The measurement uses an event sample corresponding to an
integrated luminosity of $0.7\,$fb$^{-1}$ collected with the D0 detector at the
Fermilab Tevatron Collider. The results are compared to predictions of a
perturbative QCD calculation at next-to-leading order in the strong coupling
with corrections for non-perturbative effects. The theory predictions describe
the data, except in the kinematic region of large dijet rapidity intervals and
large $\Delta \phi_{\rm max}$.
