The Collision Energy Dependence of Dijet Cross Sections as a Probe of BFKL Physics

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.