NLO QCD predictions for $Z+\gamma$ + jets production with Sherpa

TL;DR

This paper provides precise NLO QCD predictions for Z plus photon and jets production at the LHC using Sherpa, including full offshell Z decays, reducing uncertainties and aligning well with experimental data.

Contribution

It introduces a comprehensive NLO QCD simulation of Z+γ+jets production within Sherpa, including offshell effects and a detailed method for combining with Z+jets simulations.

Findings

Reduced systematic uncertainties with NLO corrections.

Good agreement with 8 TeV experimental data.

Predictions extended to 13 TeV with uncertainty analysis.

Abstract

We present precise predictions for prompt photon production in association with a $Z$ boson and jets. They are obtained within the Sherpa framework as a consistently merged inclusive sample. Leptonic decays of the $Z$ boson are fully included in the calculation with all offshell effects. Virtual matrix elements are provided by OpenLoops and parton shower effects are simulated with a dipole parton shower. Thanks to the NLO QCD corrections included not only for inclusive $Z\gamma$ production but also for the $Z\gamma$ + 1-jet process we find significantly reduced systematic uncertainties and very good agreement with experimental measurements at $\sqrt{s}=8$ TeV. Predictions at $\sqrt{s}=13$ TeV are displayed including a study of theoretical uncertainties. In view of an application of these simulations within LHC experiments, we discuss in detail the necessary combination with a simulation of the $Z$ + jets final state. In addition to a corresponding prescription we introduce recommended cross checks to avoid common pitfalls during the overlap removal between the two samples.