Z0 - boson production in association with a top anti-top pair at NLO accuracy with parton shower effects

Abstract

We present predictions for the production cross section of a Standard Model Z0-boson in association with a top-antitop pair at the next-to-leading order accuracy in QCD, matched with shower Monte Carlo programs to evolve the system down to the hadronization energy scale. We adopt a framework based on three well established numerical codes, namely the POWHEG-BOX, used for computing the cross section, HELAC-NLO, which generates all necessary input matrix elements, and finally a parton shower program, such as PYTHIA or HERWIG, which allows for including t-quark and Z0-boson decays at the leading order accuracy and generates shower emissions, hadronization and hadron decays.

Figures (5)

• Figure 1: Transverse momentum (left) and rapidity (right) distributions of the $Z^0$-boson at NLO and after first radiation (PowHel). The lower panels show the ratio of the two predictions with combined uncertainties.
• Figure 2: Transverse momentum (left) and rapidity (right) distributions of the hardest jet after decay and after full SMC. The lower panels show the ratio of all predictions to PowHel+SMC using PYTHIA.
• Figure 3: Transverse momentum (left) and rapidity (right) distributions of the hardest jet after decay and after full SMC (PYTHIA), under selection cuts (1--8) implemented at both levels. The lower panels show the ratio of the predictions at different levels.
• Figure 4: Invariant mass distribution of the t-quark reconstructed from the decay products at both decay and full SMC levels, for the t$\bar{{\rm t}}Z$ signal and, at the decay level, for one background (t$\bar{{\rm t}}$+jet) after selection cuts (1--8) (wider distributions in abscissa values) and after selection cuts (1--10) (narrower distributions).
• Figure 5: Distribution of the missing transverse momentum after decay, under physical cuts (1--10) applied to the signal (t$\bar{{\rm t}}Z$) and to one background (t$\bar{{\rm t}}$+jet).