VINCIA User Reference

April 2015 © P. Z. Skands, W. T. Giele, D. A. Kosower, E. Laenen, A. Larkoski, J. J. Lopez-Villarejo, M. Ritzmann

The VINCIA code is a plugin to the high-energy physics event generator PYTHIA 8. It is based on the dipole-antenna picture of Quantum Chromodynamics (QCD) and focusses on describing jets and jet substructure with high precision. It is currently implemented for QCD final-state evolution and includes helicity dependence, for massless partons, and mass corrections, for massive ones.

LO and NLO matrix elements can be incorporated in the evolution, as process-dependent 2→n antenna functions. In hard parts of phase space, these functions generate matrix-element corrections to the shower. In soft parts, they should improve the logarithmic accuracy of it, via unitarity. Due to the Markovian nature of VINCIA's correction scheme, very high orders of matching can be achieved with only a modest increase in calculational time per unweighted event.

The remaining perturbative uncertainties are estimated by systematic (and automated) variations of scales, shower functions, evolution variables, etc. In the automated mode, a vector of output weights is produced for each event, the central value of which is unity (for an ordinary unweighted event sample), with the uncertainty variations spreading out around it. The calculation is significantly faster than generating N separate samples, and there is only one event sample to analyse, pass through detector simulations, etc.

Event Generation. When activated, VINCIA replaces the internal PYTHIA parton cascades. The rest of the run proceeds as a normal PYTHIA 8 run, i.e., using the same functions to initialize, generate, analyse, and store events as usual. Hadronization is performed as usual in PYTHIA, with the Lund string fragmentation model. In addition, runtime displays with plots updated in realtime can be created using the VINCIAROOT interface.

This documentation contains brief descriptions of each of the user-specifiable parameters of the VINCIA code, together with instructions how to install, link, and initialize it. Use the menu to the left to navigate. These files are purely for documentation and should not be modified by the user. Instead, see the section on Initialization for how to set and change parameters.

Types of Parameters

As in PYTHIA 8, there are 4 types of parameters:

Note: both PYTHIA and VINCIA interpret parameter names in a case-insensitive (but spelling-sensitive!) way.

VINCIA and PYTHIA

To ensure accurate reproducibility, when quoting VINCIA results, please state both the exact PYTHIA and VINCIA versions used, along with any relevant non-default settings (for both programs). On plots, please give both PYTHIA and VINCIA versions.

VINCIA relies on PYTHIA 8 for both technical aspects (everything from four-vectors and the event record to its particle and settings database structures) and physics (e.g., particle decays and hadronization). When citing the VINCIA code, please respect the work of the PYTHIA authors by including a reference to PYTHIA as well, see the section on useful references.

Name

The name VINCIA stands for "VIrtual Numerical Collider with Interleaved Antennae". With roots in PYTHIA - a name taken from ancient greek mythology - the naming of VINCIA is also intended to carry an allusion to the name of Leonardo da Vinci, as a representative of creativity and science in the renaissance era. The logo of VINCIA is the "Vitruvian Man", by da Vinci, a choice which also reflects the combination of art and accuracy which is necessary to write a good event generator. Finally, the logo contains a further indirect connection to the classical era, via its namesake, Vitruvius, a first-century (BC) Roman author, architect, and engineer.

Licence

VINCIA is licenced under the GNU GPL version 2. Please respect the MCnet Guidelines for Event Generator Authors and Users.