Initial State Radiation in the Herwig 7 Angular-Ordered Parton Shower

TL;DR

This paper investigates how different interpretations of the ordering variable in angular-ordered parton showers affect their accuracy in simulating initial-state radiation, and presents a tuned recoil scheme for improved phenomenological predictions.

Contribution

It introduces a recoil scheme consistent for both initial- and final-state radiation and provides tuned parameters for the Herwig 7 angular-ordered parton shower.

Findings

Optimal strong coupling and intrinsic transverse momentum values were determined.

The tuned showers accurately reproduce Z-boson production at the LHC.

Phenomenological studies of Drell-Yan processes at various energies were performed.

Abstract

We study the simulation of initial-state radiation in angular-ordered parton showers in order to investigate how different interpretations of the ordering variable affect the logarithmic accuracy of such showers. This also enables us to implement a recoil scheme which is consistent between final-state and initial-state radiation. We present optimal values of the strong coupling and intrinsic transverse momentum to be used in each version of the parton shower, tuned using $Z^0$-boson production at the LHC at 7 TeV. With these tuned showers, we perform a phenomenological study of the Drell-Yan process at several centre-of-mass energies.