Top Pair Threshold Revisited

TL;DR

This paper revisits the non-relativistic Green's function formalism for top quark pair production near threshold, updating it for modern use and integrating it into the Pythia event generator.

Contribution

It revives and refines a 35-year-old formalism, making it suitable for Monte Carlo simulations and current experimental conditions.

Findings

Below-threshold cross section estimated at 6.5 pb, aligning with CMS and ATLAS data.

Formalism integrated into Pythia for detailed phenomenological studies.

Provides a consistent framework for analyzing top pair production near threshold.

Abstract

Recently the CMS and ATLAS collaborations have found evidence for an unexpectedly large ttbar cross section in the threshold region, with an excess of the order of 5-10 pb relative to continuum perturbative calculations. A convenient approach to the theoretical study of this region, unifying the above- and below-threshold behaviour, is the non-relativistic Green's function formalism. It was first applied to top production more than 35 years ago, well before the discovery of the top. We therefore revive and dissect the old formalism, and put it back together in a more consistent form, suited for Monte Carlo event generation. Combined with some practical prescriptions, it can be applied to current conditions. As an example, the below-threshold cross section comes out to be of the order of 6.5 pb, i.e. comparable with the CMS and ATLAS numbers. The new code is publicly available in the Pythia event generator so can be used for more detailed comparisons.