  We propose a new approach to the LHC dark matter search analysis within the
effective field theory (EFT) framework by utilising the K-matrix unitarisation
formalism. This approach provides a reasonable estimate of the dark matter
production cross section at high energies, and hence allows reliable bounds to
be placed on the cut-off scale of relevant operators without running into the
problem of perturbative unitarity violation. We exemplify this procedure for
the effective operator D5 in monojet dark matter searches in the collinear
approximation. We compare our bounds to those obtained using the truncation
method and identify a parameter region where the unitarisation prescription
leads to more stringent bounds.
