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

Abstract

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 summaryProgram title: HELAC-Onia 2.0Catalogue identifier: AEPR_v2_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEPR_v2_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 1513282No. of bytes in distributed program, including test data, etc.: 17036140Distribution format: tar.gzProgramming 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_0Journal reference of previous version: Comput. Phys. Comm. 184(2013)2562External routines: LHAPDFDoes the new version supersede the previous version?: YesNature 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.Solution method: Based on a recursion relation, the program is able to calculate the helicity amplitudes of the high-multiplicity heavy- quarkonium-production processes. Several modules are also designed for dedicated simulations: 1.The code has been interfaced with the parton shower Monte Carlo programs;2.A decay module to let heavy quarkonia decay with correct spin-correlations has been implemented;3.The code estimates the theoretical uncertainties and analyzes the generated events on the fly;4.The code is compliant with multi-threading/multi-core usage or cluster processors.Reasons for new version: Improved and expanded functionalities.Summary of revisions: Many new features were added and several important bugs were fixed. The new features extend the range of the physical applications. With the new interface, it also helps to improve the user-friendliness of the program.Running time: It depends on the process to be calculated and the required accuracy.