GR@PPA 2.9: radiation matching for simulating photon production processes in hadron collisions

TL;DR

GR@PPA 2.9 is a new event generator package that accurately simulates photon production in hadron collisions by combining matrix element calculations with parton-shower models, including associated parton processes.

Contribution

The paper introduces GR@PPA 2.9, a novel event generator that integrates matrix elements with parton showers for photon production, including up to two associated partons.

Findings

Demonstrates large contributions from parton-associated processes in photon production.

Provides practical instructions for installation and use.

Shows consistent combination of matrix elements with parton-shower simulations.

Abstract

We release an event generator package, GR@PPA 2.9, for simulating the direct (single) photon and diphoton (double photon) production in hadron collisions. The included programs were used in our previous studies, in which we have explicitly shown large contributions from parton-associated processes. The programs consistently combine simulations based on matrix elements with parton-shower simulations that reproduce the multiple parton radiation and quark fragmentation to photons. The matrix elements include associated parton production processes up to two partons. We provide instructions for the installation and execution of the programs in this article. The practical performance is also presented.