Hadroproduction of $W^+ W^- b \bar{b}$ at NLO accuracy matched with shower Monte Carlo programs

TL;DR

This paper computes the differential cross section for W+W- b b̄ production at NLO accuracy matched with Shower Monte Carlo, including off-shell effects and spin correlations, providing detailed predictions for Tevatron and LHC.

Contribution

It introduces a comprehensive NLO QCD calculation for W+W- b b̄ production matched with SMC, incorporating off-shell effects, spin correlations, and a new decay program DECAYER.

Findings

Differences observed between full off-shell calculations and narrow width approximation.

Predictions show significant effects of off-shell and spin correlation treatments.

The DECAYER program effectively simulates t-quark decays with finite width and spin correlations.

Abstract

We present the computation of the differential cross section for the process $pp(\bar{p}) \to (W^+\,W^-\,b\,\bar{b} \to)\;e^+\,\nu_e\,\mu^-\,\bar{\nu}_\mu\,b\, \bar{b}+X$ at NLO QCD accuracy matched to Shower Monte Carlo (SMC) simulations using PowHel, on the basis of the interface between HELAC-NLO and POWHEG-BOX. We include all resonant and non-resonant contributions. This is achieved by fully taking into account the effect of off-shell t-quarks and off-shell W-bosons in the complex mass scheme. We also present a program called DECAYER that can be used to let the t-quarks present in the event files for $pp(\bar{p}) \to {t\,\bar{t}\,X}$ processes decay including both the finite width of the t-quarks and spin correlations. We present predictions for both the Tevatron and the LHC, with emphasis on differences emerging from three different $W^+\,W^-\,b\,\bar{b}$ hadroproduction computations: (i) full implementation of the $p\,p(\bar{p}) \to W^+\,W^-\,b\,\bar{b}$ process, (ii) generating on-shell t-quarks pushed off-shell with a Breit-Wigner finite width and decayed by DECAYER, and (iii) on-shell t-quark production followed by decay in the narrow width approximation, as described by the SMC.