Event generation with exponential scaling in multiplicity using AmpliCol

TL;DR

AmpliCol introduces an efficient method for generating high-multiplicity LHC events by combining leading-colour approximation with reweighting to full-colour accuracy, achieving exponential scaling instead of factorial growth.

Contribution

The paper extends a two-step event generation strategy to general Standard Model processes and presents AmpliCol, a standalone tool that significantly improves computational efficiency.

Findings

Runtime scales exponentially with multiplicity, not factorial.

AmpliCol efficiently generates events at high multiplicities.

Benchmarking shows stable performance across various processes.

Abstract

Efficient generation of LHC events is hindered by the rapidly rising cost of evaluating QCD matrix elements with increasing multiplicity. We build on a recently proposed two-step strategy in which unweighted events are first generated using the leading-colour (LC) approximation and then reweighted to full-colour (FC) accuracy, utilising the LC integration efficiency while recovering the exact FC prediction. In this work we extend the method to general Standard Model processes and present AmpliCol, a standalone implementation designed for LHC collisions. We benchmark multi-jet, $t\bar{t}$+jets, $ZZ$+jets, and Drell-Yan+jets production, measuring the time required to obtain a fixed number of unweighted events at FC accuracy. Across all processes, the runtime exhibits a stable exponential scaling with multiplicity, far milder than the factorial growth of conventional matrix-element generators. This demonstrates that the AmpliCol code enables efficient event generation at multiplicities that are otherwise computationally prohibitive.