NLO QCD matrix elements + parton showers in e+e- -> hadrons

TL;DR

This paper introduces a new method to combine NLO QCD calculations with parton showers, improving the accuracy of simulating multi-jet events in electron-positron annihilation and better matching experimental data.

Contribution

It presents a novel approach to merge multiple NLO calculations with parton showers into a unified event simulation framework.

Findings

Accurately describes multi-jet configurations at NLO in QCD.

Achieves improved agreement with LEP experimental data.

Provides detailed analysis of renormalisation scale effects.

Abstract

We present a new approach to combine multiple NLO parton-level calculations matched to parton showers into a single inclusive event sample. The method provides a description of hard multi-jet configurations at next-to leading order in the perturbative expansion of QCD, and it is supplemented with the all-orders resummed modelling of jet fragmentation provided by the parton shower. The formal accuracy of this technique is discussed in detail, invoking the example of electron-positron annihilation into hadrons. We focus on the effect of renormalisation scale variations in particular. Comparison with experimental data from LEP underlines that this novel formalism describes data with a theoretical accuracy that has hitherto not been achieved in standard Monte Carlo event generators.