  We reemphasise the usefulness of angular correlations in LHC searches for
missing transverse energy ($E_T^{\mathrm{miss}}$) signatures that involve jet
$(j)$ pairs with large invariant mass. For the case of mono-jet production via
gluon-fusion, we develop a realistic analysis strategy that allows to split the
dark matter (DM) signal into distinct one jet-like and two jet-like event
samples. By performing state-of-the-art Monte Carlo simulations of both the
mono-jet signature and the standard model background, it is shown that the
dijet azimuthal angle difference $\Delta \phi_{j_1 j_2}$ in $2 j
+E_T^{\mathrm{miss}}$ production provides a powerful discriminant in realistic
searches. Employing a shape fit to $\Delta \phi_{j_1 j_2}$, we then determine
the LHC reach of the mono-jet channel in the context of spin-0 $s$-channel DM
simplified models. The constraints obtained by the proposed $\Delta \phi_{j_1
j_2}$ shape fit turn out to be significantly more stringent than those that
derive from standard $E_T^{\mathrm{miss}}$ shape analyses.
