Reweighting QCD matrix-element and parton-shower calculations

TL;DR

This paper introduces a method to efficiently evaluate theoretical uncertainties in QCD simulations by computing variational event weights on-the-fly, reducing computational costs.

Contribution

It presents a novel implementation that traces full alpha_s and PDF dependences, including parton-shower components, within the Sherpa framework.

Findings

Significantly reduces computational costs for uncertainty estimation.

Validates the method within the Sherpa event-generator framework.

Enables on-the-fly evaluation of theoretical uncertainties.

Abstract

We present the implementation and validation of the techniques used to efficiently evaluate parametric and perturbative theoretical uncertainties in matrix-element plus parton-shower simulations within the Sherpa event-generator framework. By tracing the full $\alpha_s$ and PDF dependences, including the parton-shower component, as well as the fixed-order scale uncertainties, we compute variational event weights on-the-fly, thereby greatly reducing the computational costs to obtain theoretical-uncertainty estimates.