Angular correlations of lepton pairs from vector boson and top quark decays in Monte Carlo simulations
S. Frixione, E. Laenen, P. Motylinski, B. R. Webber
TL;DR
The paper tackles the challenge of predicting lepton spectra from vector-boson and top-quark decays with correct production angular correlations in NLO-matched parton showers.It introduces a practical hit-and-miss approach that uses universal upper bounds derived from undecayed production matrix elements to generate leptonic momenta while retaining production spin effects.The bounds are derived for vector-boson and top decays, and generalize to multiple decays, enabling a tractable method compatible with MC@NLO/POWHEG frameworks.Illustrative MC@NLO results for $t\bar{t}$ and single-top production at the LHC and Tevatron demonstrate the method's applicability and its potential to improve lepton-spectrum predictions in complex final states.
Abstract
We explain how angular correlations in leptonic decays of vector bosons and top quarks can be included in Monte Carlo parton showers, in particular those matched to NLO QCD computations. We consider the production of $n$ pairs of leptons, originating from the decays of $n$ electroweak vector bosons or of $n$ top quarks, in the narrow-width approximation. In the latter case, the information on the $n$ $b$ quarks emerging from the decays is also retained. We give results of implementing this procedure in MC@NLO