A positive-weight next-to-leading order simulation of weak boson pair production

Keith Hamilton

doi:10.1007/jhep01(2011)009

Abstract

In this article we describe simulations of ZZ, WZ and WW production based on the positive weight next-to-leading-order matching scheme, Powheg, in the Herwig++ event generator. Building on earlier efforts within the Herwig++ framework, the simulation includes a full description of truncated showering effects, required to correctly model soft, wide angle, emissions in angular-ordered parton showers. We utilize simple relations among each of the diboson cross sections, holding to order alpha_S, in constructing the simulation. Spin correlation effects are also included in the decays of the vector bosons at the tree order. A large part of this work is concerned with a full and thorough validation of the simulations through comparisons with alternative methods and calculations.

Highlights

Combined, has the potential to surpass the sensitivity of the LEP2 data to such effects
In this article we describe simulations of ZZ, W ±Z and W +W − production based on the positive weight next-to-leading-order (NLO) matching scheme, Powheg, in the Herwig++ event generator
In order to check the calculation of the Powheg differential cross section and B (ΦB) functions, eqs. (2.1)–(2.2), we have compared our predictions for total cross sections and numerous inclusive observables against those of the NLO Monte Carlo calculator Mcfm [36, 90, 91]

Summary

Introduction

Combined, has the potential to surpass the sensitivity of the LEP2 data to such effects. Further improvements were made by Campbell and Ellis who extended the results of the latter work beyond the narrow width approximation, including contributions from singly resonant Feynman diagrams and interference effects between intermediate Z bosons and photons [36] Following these results, in the early part of the last decade, a number of ground breaking developments took place in the field of Monte Carlo event generator research, most significantly, the invention of the CKKW(-L) and MLM algorithms, combining parton shower simulations together with those based on tree level matrix elements [37,38,39,40,41,42] and, separately, the Mc@nlo [43] and Powheg [44, 45] formalisms for consistently including fully differential NLO corrections in parton shower simulations. For reasons of technical simplicity, greatly increased computational efficiency, and minded to best utilize the existing Herwig++ infrastructure, e.g. the facility to include higher order QCD and QED corrections to the decays of vector bosons, we have based our work on the original calculations of Frixione et al [28, 32, 33], as in Mc@nlo, valid in the double pole approximation

Objectives

Results

Conclusion