  The dependence of the subprocess cross section for dijet production at fixed
transverse momentum on the (large) rapidity separation Delta y of the dijets
can be used to test for `BFKL physics', i.e. the presence of higher--order
(alphas log(Delta y)^n contributions. Unfortunately in practice these subtle
effects are masked by the additional, stronger dependence arising from the
parton distributions. We propose a simple ratio test using two different
collider energies n which the parton distribution dependence largely cancels.
Such a ratio does distinguish between the `asymptotic' analytic BFKL and
lowest-order QCD predictions. However, when subasymptotic effects from overall
energy-momentum conservation are included, the BFKL predictions for present
collider energies change qualitatively. In particular, the real gluon emission
contributions to the BFKL cross section are suppressed. The proposed ratio
therefore provides an interesting laboratory for studying the interplay of
leading-logarithm and kinematic effects.
