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	PYTHIA 8




Authors:



	P. Skands H. Brooks A. Lifson R. Verheyen



Additional Contributors:



	N. Fischer W. T. Giele L. Hartgring D. A. Kosower E. Laenen A. J. Larkoski J. J. Lopez-Villarejo S. Prestel M. Ritzmann



VINCIA is supported by:

VINCIA LHC

The VINCIA code is a plugin to the high-energy physics event generator PYTHIA 8.2.

Starting from PYTHIA 8.3, VINCIA will be distributed as part of the PYTHIA source code, and hence this standalone plugin will not be relevant to PYTHIA 8.3 users.

VINCIA is based on the dipole-antenna picture of Quantum Chromodynamics (QCD) and focusses on describing jets and jet substructure with high precision.

The current version includes both initial- and final-state QCD and QED showers.

In previous versions of VINCIA, LO matrix elements could be incorporated in the evolution, as process-dependent 2→n antenna functions. This functionality was removed in the 2.3 series as part of an ongoing effort to move from a matrix-element interface based on MadGraph 4 to one based on MadGraph 5. At the same time, VINCIA is in the process of being merged into the PYTHIA code, where it will be available starting from PYTHIA 8.3. Future development of VINCIA (such as ME corrections based on MG5) will then take place as part of the PYTHIA development.

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. Hadronisation is performed with the usual Lund string fragmentation model, with VINCIA-specific default parameters. Instead of the PYTHIA initialisation step in the main program the same function is called on the VINCIA object. Apart from that, the events are generated and analysed as in a normal PYTHIA 8 run. In addition, runtime displays with plots updated in realtime can be created using the LiveDisplays interface.

Installation

The following simple steps set up a standalone VINCIA installation from scratch, complete with linking to PYTHIA 8 and ready-to-run example programs (assuming you have working C++ and F77 compilers which are mutually compatible):

Download and compile PYTHIA 8.
Download VINCIA. Place the tarball in your PYTHIA 8 main directory (e.g., pythia8215/), and untar it.
Go to the thus created subfolder vincia-N.N.NN/ (with N.N.NN being the version number you downloaded) and run "./configure" (use "./configure --help" to see configuration options), then run "make".
Move to the examples/ subfolder ("cd examples") and run "make" there. The default test program should now be ready to run: ./vincia01

Linking and initialization of VINCIA is done automatically when the VinciaPlugin object is created.

More examples, and more complete instructions on how to install, link, and use VINCIA also in more complicated setups can be found in the HTML User Reference and Manual and in the README.

Documentation

User Guides and Reviews

VINCIA HTML User Reference: Brief descriptions of each of the user-specifiable parameters of the VINCIA code.
Introduction to QCD: Lecture notes for a course given at TASI 2012 (updated several times since), with special focus on event generators, showers, and matching.
General-Purpose Event Generators for LHC Physics: long review by the MCnet authors (including Herwig, Pythia, and Sherpa) on the physics of event generators.

VINCIA Articles & References

2019	Coherent Showers in Decays of Coloured Resonances. Introduction of "resonance-final" (RF) antennae with focus on radiation in top decays.
2017	Final-State QED Multipole Radiation in Antenna Parton Showers. Definition of VINCIA's coherent QED showers, by R. Kleiss and R. Verheyen.
	Helicity Antenna Showers for Hadron Colliders. Initial-state showers and matrix-element corrections with helicity dependence.
	Combining states without scale hierarchies with ordered parton showers. Iterated ME corrections for strongly ordered showers. Multi-leg merging with ME-corrected showers.
2016	A framework for second-order parton showers. Conceptual proposal for extending antenna showers with 2→4 branchings and one-loop-corrected 2→3 ones.
	Vincia for Hadron Colliders. Comprehensive reference for initial-state showers in VINCIA.
2013	Antenna Showers with One-Loop Matrix Elements. Original reference for (multileg) NLO matching with VINCIA. Incorporating the NLO correction to ee → 3 jets in the evolution from ee → 2 jets. Studies of dependence on evolution and renormalization scale choices. NLO-corrected tune to ee event-shape, jet-rate, and fragmentation data.
2013	Helicity-Dependent Showers and Matching with VINCIA. First paper on helicity-dependence in VINCIA. Using individual helicity amplitudes (squared) to drive the matrix-element corrections improves the speed of the matching algorithm. Comparisons to VINCIA without helicity dependence and to CKKW-based SHERPA.
2012	Antenna Showers with Hadronic Initial States. First VINCIA paper treating initial-state showers.
2011	Efficient Matrix-Element Matching with Sector Showers. First paper on sector-based final-state showers (and corresponding sector-based GKS matching). Speed comparison to CKKW-based SHERPA.
2011	Timelike Dipole-Antenna Showers with Massive Fermions. Mass corrections to final-state phase space and antenna functions. Comparisons to analytical resummation, b-quark fragmentation, and b-tagged events shapes.
2011	Higher-order Corrections to Timelike Jets. Original reference for unitarity-based "GKS" matching (iterated matrix-element corrections), smooth ordering, and automated uncertainty bands by Sudakov reweighting. Comparisons to LEP for massless quarks.
2008	Time-Like Showers Based on Dipole-Antenna Radiation Functions. Massless quarks + analytical comparisons to ARIADNE functions + numerical comparisons to PYTHIA 8 for Z decays
2007	A Simple Shower and Matching Algorithm. Original VINCIA antenna-shower reference. Basic shower formalism, gluons only + first comparison to PYTHIA 8