A Higher Order Perturbative Parton Evolution Toolkit (HOPPET)

TL;DR

HOPPET is a Fortran 95 toolkit for efficient and accurate DGLAP evolution of parton distribution functions, supporting unpolarized and polarized cases with flexible input and extension capabilities.

Contribution

It introduces a grid-based, high-precision method for PDF evolution with a user-friendly interface and extendable structure, covering NNLO unpolarized and NLO polarized evolutions.

Findings

Achieves good speed and accuracy in PDF evolution

Supports NNLO unpolarized and NLO polarized evolutions

Provides a flexible, extendable code structure

Abstract

This document describes a Fortran 95 package for carrying out DGLAP evolution and other common manipulations of parton distribution functions (PDFs). The PDFs are represented on a grid in x-space so as to avoid limitations on the functional form of input distributions. Good speed and accuracy are obtained through the representation of splitting functions in terms of their convolution with a set of piecewise polynomial basis functions, and Runge-Kutta techniques are used for the evolution in Q. Unpolarised evolution is provided to NNLO, including heavy-quark thresholds in the MSbar scheme, and longitudinally polarised evolution to NLO. The code is structured so as to provide simple access to the objects representing splitting functions and PDFs, making it possible for a user to extend the facilities already provided. A streamlined interface is also available, facilitating use of the evolution part of the code from F77 and C/C++.