Speaker
Peter Skands
(Monash University (AU))
Description
We present the first public implementation of antenna-based QCD initial- and final-state showers. The shower kernels are $2\to 3$ antenna functions, which capture not only the collinear dynamics but also the leading soft (coherent) singularities of QCD matrix elements. We define the evolution measure to be inversely proportional to the leading poles, hence gluon emissions are evolved in a $p_\perp$ measure inversely proportional to the eikonal, while processes that only contain a single pole (e.g., $g\to q\bar{q}$) are evolved in virtuality. Non-ordered emissions are allowed, suppressed by an additional power of $1/Q^2$. Recoils and kinematics are governed by exact on-shell $2\to 3$ phase-space factorisations. Tree-level matrix-element corrections a la GKS are included for QCD up to $\mathcal{O}(\alpha_s^4)$ (4 jets), and for Drell-Yan and Higgs production up to $\mathcal{O}(\alpha_s^3)$ ($V/H$ + 3 jets). The perturbative shower uncertainties can be evaluated by variations of renormalization scales and non-singular terms, including an automated mode in which each event is accompanied by a vector of "uncertainty weights". As a proof-of-concept for the applicability of our method we focus on Z boson production at the LHC. The resulting algorithm has been made publicly available in VINCIA 2.0, which is written as a simple plug-in to the PYTHIA 8 event generator.
Primary author
Peter Skands
(Monash University (AU))
Co-author
Nadine Fischer
(KIT - Karlsruhe Institute of Technology (DE))
