Automatic generation of quarkonium amplitudes in NRQCD

TL;DR

This paper introduces an automated method for calculating tree-level amplitudes involving heavy quark pairs in NRQCD, streamlining quarkonium production and decay analysis in collider physics.

Contribution

The authors develop a novel, automated approach to evaluate NRQCD short-distance coefficients for arbitrary quarkonium states, integrated into MadGraph.

Findings

Method successfully computes amplitudes for various quarkonium states.

Implementation in MadGraph demonstrates practical applicability.

Results facilitate more efficient collider phenomenology studies.

Abstract

We present a simple method to automatically evaluate arbitrary tree-level amplitudes involving the production or decay of a heavy quark pair QQbar in a generic {2S+1}L_J^[1,8] state, i.e., the short distance coefficients appearing in the NRQCD factorization formalism. Our approach is based on extracting the relevant contributions from the open heavy quark-antiquark amplitudes through an expansion with respect to the quark-antiquark relative momentum and the application of suitable color and spin projectors. To illustrate the capabilities of the method and its implementation in MadGraph a few applications to quarkonium collider phenomenology are presented.