W and Z/gamma* boson production in association with a bottom-antibottom pair

TL;DR

The paper delivers fully automated, NLO QCD predictions for l nu b bbar and l l b bbar production with massive bottom quarks and exact spin correlations, matched to parton showers via MC@NLO. It shows that NLO corrections—especially gluon-initiated channels at the LHC—significantly affect rates and kinematic distributions and that differences between W b bbar and Z b bbar arise from their distinct production mechanisms. By retaining mb and including showering, hadronization, and spin correlations, the work provides high-precision, hadron-level backgrounds relevant for Higgs (WH/ZH) searches and top-quark studies, with public event files enabling broader use.

Abstract

We present a study of lνb\bar{b} and l+ l- b\bar{b} production at hadron colliders. Our results, accurate to the next-to-leading order in QCD, are based on automatic matrix-element calculations performed by MadLoop and MadFKS, and are given at both the parton level, and after the matching with the Herwig event generator, achieved with aMC@NLO. We retain the complete dependence on the bottom-quark mass, and include exactly all spin correlations of final-state leptons. We discuss the cases of several observables at the LHC which highlight the importance of accurate simulations.

Figures (12)

• Figure 1: Representative diagrams contributing to $\ell\nu b\bar{b}$ and $\ell^+ \ell^- b\bar{b}$ production at the leading order. $\ell\nu b\bar{b}$ production can proceed only via a $q\bar{q}^\prime$ channel, diagram (a). For $\ell^+ \ell^- b\bar{b}$ production the $q\bar{q}$ channel, diagram (a), is dominant at the Tevatron, while the $gg$ channel, diagram (b), largely dominates at the LHC.
• Figure 2: Fractions of events (in percent) that contain: zero $b$-jets, exactly one $b$-jet, and exactly two $b$-jets. The rightmost bin displays the fraction of $b$-jets which are $bb$-jets. The two insets show the ratio of the a MC@NLO results over the corresponding NLO (solid), a MC@LO (dashed), and LO (symbols) ones, separately for $Wb\bar{b}$ (upper inset) and $Zb\bar{b}$ (lower inset) production.
• Figure 3: Invariant mass distribution of final-state lepton pairs, as predicted by a MC@NLO.
• Figure 4: Transverse momentum of the charged leptons in $\ell\nu b\bar{b}$ (left panel) and $\ell^+ \ell^- b\bar{b}$ (right panel) production, shown separately for positive and negative charges. The upper and middle insets follow the same patterns as those in fig. \ref{['fig:rates']}. The lower inset (magenta solid histogram) is the ratio of the a MC@NLO results relevant to positively-charged leptons over those relevant to negatively-charged ones.
• Figure 5: As in fig. \ref{['fig:WZbb_pt_e']}, for the pseudorapidity of the charged leptons.