HELAC-Onia 2.0: An upgraded matrix-element and event generator for heavy quarkonium physics

We present an upgraded version (denoted as version 2.0) of the program HELAC-Onia for the automated computation of heavy-quarkonium helicity amplitudes within non-relativistic QCD framework. The new code has been designed to include many new and useful features for practical phenomenological simulations. It is designed for job submissions under cluster environment for parallel computations via Python scripts. We have interfaced HELAC-Onia to the parton shower Monte Carlo programs Pythia 8 and QEDPS to take into account the parton-shower effects. Moreover, the decay module guarantees that the program can perform the spin-entangled (cascade-)decay of heavy quarkonium after its generation. We have also implemented a reweighting method to automatically estimate the uncertainties from renormalization and/or factorization scales as well as parton-distribution functions to weighted or unweighted events. A further update is the possibility to generate one-dimensional or two-dimensional plots encoded in the analysis files on the fly. Some dedicated examples are given at the end of the writeup. Program title: HELAC-Onia 2.0 Catalogue identifier: AEPR_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEPR_v2_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 1513282 No. of bytes in distributed program, including test data, etc.: 17036140 Distribution format: tar.gz Programming language: Python, Fortran 77, Fortran 90, C++. Operating system: Unix-like platform. Classification: 4.4, 11.1, 11.2, 11.5. Catalogue identifier of previous version: AEPR_v1_0 Journal reference of previous version: Comput. Phys. Comm. 184(2013)2562 External routines: LHAPDF Does the new version supersede the previous version?: Yes Nature of problem: Heavy quarkonium production processes provide an important way to investigate QCD in its poorly known non-perturbative regime. Its production mechanism has attracted extensive interests from the high-energy physics community in decades. The qualitative and quantitative description of heavy-quarkonium production requires complex perturbative computations for high-multiplicity processes in the framework of the well established non-relativistic effective theory, NRQCD, and reliable Monte Carlo simulations to reproduce the collider environment. Sol