High-energy logarithms and precision at the LHC

Abstract

We address the breakdown of fixed-order perturbation theory due to logarithms in $s/p_t^2$ for processes involving two jets or more at the energies currently explored at the LHC. The problem manifests itself in various ways: an obvious breakdown of the perturbative series for some kinematic distributions, highly asymmetric scale variations in other distributions, and the need for an artificially large renormalisation scale to even achieve numerical stability. As we demonstrate, the problem is solved through the resummation of these high-energy logarithms. The customary choice of a large renormalisation scale of $m_{j_1j_2}$ offers no systematic resolution. This breakdown in fixed order predictions is illustrated for the production of $Z$+dijets. We show that resummed predictions obtained using \HighEJ matched to fixed order obtain accurate predictions for all the relevant distributions investigated in a recent ATLAS measurement.