The Les Houches Accord PDFs (LHAPDF) and Lhaglue

TL;DR

The paper addresses the need for a scalable, modular interface to parton distribution functions (PDFs) that can handle many sets and uncertainty representations beyond PDFLIB. It presents LHAPDF, a framework that separates parameter files from compiled code and enables on-the-fly evolution, along with a multi-set concept for error PDFs. The development timeline (V1–V4) highlights integration of grid-based and analytic approaches, a PDFLIB-like LHAGLUE interface, and inclusion of photon/pion PDFs, plus a revised numbering scheme. LHAPDF 4.1 (Aug 2005) further standardised installation and compatibility, positioning LHAPDF/LHAGLUE as the de facto replacement for PDFLIB access in Monte Carlo workflows.

Abstract

We describe the development of the LHAPDF library from its initial implementation following the Les Houches meeting in 2001 to its present state as a functional replacement for PDFLIB. Brief details are given of how to install and use the library together with the PDF sets available. We also describe LHAGLUE, an add-on PDFLIB look-a-like interface to LHAPDF, which facilitates using LHAPDF with existing Monte Carlo generators such as PYTHIA and HERWIG.