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LHAPDF6: parton density access in the LHC precision era

Research output: Contribution to Journal/MagazineJournal articlepeer-review

Published
  • A.G. Buckley
  • James Edward Ferrando
  • Stephen Lloyd
  • Karl Nordstrom
  • B. Page
  • Martin Rüfenacht
  • Marek Schoenherr
  • G Watt
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Article number132
<mark>Journal publication date</mark>20/03/2015
<mark>Journal</mark>Eur. Phys. J.
Issue number75
VolumeC
Publication StatusPublished
<mark>Original language</mark>English

Abstract

The Fortran LHAPDF library has been a long-term workhorse in particle physics, providing standardised access to parton density functions for experimental and phenomenological purposes alike, following on from the venerable PDFLIB package. During Run 1 of the LHC, however, several fundamental limitations in LHAPDF’s design have became deeply problematic, restricting the usability of the library for important physics-study procedures and providing dangerous avenues by which to silently obtain incorrect results. In this paper we present the LHAPDF 6 library, a ground-up re-engineering of the PDFLIB/LHAPDF paradigm for PDF access which removes all limits on use of concurrent PDF sets, massively reduces static memory requirements, offers improved CPU performance, and fixes fundamental bugs in multi-set access to PDF metadata. The new design, restricted for now to interpolated PDFs, uses centralised numerical routines and a powerful cascading metadata system to decouple software releases from provision of new PDF data and allow completely general parton content. More than 200 PDF sets have been migrated from LHAPDF 5 to the new universal data format, via a stringent quality control procedure. LHAPDF 6 is supported by many Monte Carlo generators and other physics programs, in some cases via a full set of compatibility routines, and is recommended for the demanding PDF access needs of LHC Run 2 and beyond.