Accelerating LHC event generation with simplified pilot runs and fast PDFs

TL;DR

This paper presents methods to significantly speed up LHC event generation by optimizing PDF evaluation and matrix-element calculations, reducing computational costs while preserving accuracy.

Contribution

It introduces optimized algorithms for PDF evaluation and matrix-element generation, achieving approximately tenfold speed improvements in LHC event simulations.

Findings

LHAPDF and Sherpa computational footprint reduced by factors of 10

Maintained formal accuracy of event samples after optimization

Codes are publicly available for broader use

Abstract

Poor computing efficiency of precision event generators for LHC physics has become a bottleneck for Monte-Carlo event simulation campaigns. We provide solutions to this problem by focusing on two major components of general-purpose event generators: The PDF evaluator and the matrix-element generator. For a typical production setup in the ATLAS experiment, we show that the two can consume about 80% of the total runtime. Using NLO simulations of $pp\to\ell^+\ell^-+\text{jets}$ and $pp\to t\bar{t}+\text{jets}$ as an example, we demonstrate that the computing footprint of LHAPDF and Sherpa can be reduced by factors of order 10, while maintaining the formal accuracy of the event sample. The improved codes are made publicly available.