W^+W^+ plus dijet production in the POWHEGBOX

TL;DR

The paper presents the first NLO+PS implementation of a 2->4 process, W^+W^+ plus two jets, within the POWHEG BOX framework and interfaces it with PYTHIA and HERWIG. It discusses the computationally intensive nature of high-multiplicity NLO calculations, introduces efficiency techniques such as folding and tighter upper bounds, and validates the approach by comparing to pure NLO results and showered predictions. The authors provide detailed technical guidance for implementing complex processes in POWHEG BOX and demonstrate phenomenological results at 7 TeV that show good agreement for inclusive observables and highlight shower-induced effects in hadronic distributions. The work advances reliable SM background modeling for same-sign WW signatures and double parton scattering analyses, and makes the code publicly available for broader use.

Abstract

We present an implementation of the calculation of the production of W^+W^+ plus two jets at hadron colliders, at next-to-leading order (NLO) in QCD, in the POWHEG framework, which is a method that allows the interfacing of NLO calculations to shower Monte Carlo programs. This is the first 2 -> 4 process to be described to NLO accuracy within a shower Monte Carlo framework. The implementation was built within the POWHEGBOX package. We discuss a few technical improvements that were needed in the POWHEGBOX to deal with the computer intensive nature of the NLO calculation, and argue that further improvements are possible, so that the method can match the complexity that is reached today in NLO calculations. We have interfaced our POWHEG implementation with PYTHIA and HERWIG, and present some phenomenological results, discussing similarities and differences between the pure NLO and the POWHEG+PYTHIA calculation both for inclusive and more exclusive distributions. We have made the relevant code available at the POWHEGBOX web site.