Transverse-momentum resummation for heavy-quark hadroproduction

TL;DR

This paper develops a comprehensive resummation formalism for small transverse momentum distributions in heavy-quark pair production, accounting for complex color flow and azimuthal correlations, improving predictions in QCD calculations.

Contribution

It introduces a novel all-order resummation framework for heavy-quark production that includes color flow effects and azimuthal correlations at NNLL accuracy.

Findings

Resummation formalism includes color flow evolution factors.

Explicit analytical results up to NNLL accuracy.

Accounts for azimuthal correlations from soft radiation.

Abstract

We consider the production of a pair of heavy quarks ($Q{\bar Q}$) in hadronic collisions. When the transverse momentum $q_T$ of the heavy-quark pair is much smaller than its invariant mass, the QCD perturbative expansion is affected by large logarithmic terms that must be resummed to all-orders. This behavior is well known from the simpler case of hadroproduction of colourless high-mass systems, such as vector or Higgs boson(s). In the case of $Q{\bar Q}$ production, the final-state heavy quarks carry colour charge and are responsible for additional soft radiation (through direct emission and interferences with initial-state radiation) that complicates the evaluation of the logarithmically-enhanced terms in the small-$q_T$ region. We present the all-order resummation structure of the logarithmic contributions, which includes colour flow evolution factors due to soft wide-angle radiation. Resummation is performed at the completely differential level with respect to the kinematical variables of the produced heavy quarks. Soft-parton radiation produces azimuthal correlations that are fully taken into account by the resummation formalism. These azimuthal correlations are entangled with those that are produced by initial-state collinear radiation. We present explicit analytical results up to next-to-leading order and next-to-next-to-leading logarithmic accuracy.