<chapter name="Front"> 
 
<h1>PYTHIA 8</h1> 
 
<h2>Welcome to PYTHIA - The Lund Monte Carlo!</h2> 
 
<p/> 
PYTHIA 8 is the successor to PYTHIA 6, rewritten from scratch in C++. 
With the release of PYTHIA 8.1 it now becomes the official "current" 
PYTHIA version, although PYTHIA 6.4 will be supported in  parallel 
with it for some time to come. Specifically, the new version has not 
yet been enough tested and tuned for it to have reached the same level 
of reliability as the older one. This testing will only happen if 
people begin to work with the program, however, which is why we 
encourage a gradual transition to the new version, starting now. 
There are some new physics features in PYTHIA 8.1, that would make 
use of it more attractive, but also some topics still missing, where 
6.4 would have to be used. Further, many obsolete features will not 
be carried over, so for some backwards compatibility studies again 
6.4 would be the choice. 
 
<h2>Documentation</h2> 
 
On these webpages you will find the up-to-date manual for PYTHIA 8.1. 
Use the left-hand index to navigate this documentation of program 
elements, especially of all possible program settings. All parameters 
are provided with sensible default values, however, so you need only 
change those of relevance to your particular study, such as choice of 
beams, processes and phase space cuts. The pages also contain a fairly 
extensive survey of all methods available to the user, e.g. to study 
the produced events. What is lacking on these webpages is an overview, 
on the one hand, and an in-depth physics description, on the other. 
 
<p/> 
The overview can be found in the attached PDF file 
<br/><a href="pythia8100.pdf" target="page"><b>A Brief Introduction 
to PYTHIA 8.1</b></a> 
<br/>T. Sj&ouml;strand, S. Mrenna and P. Skands, 
Comput. Phys. Comm. 178 (2008) 852 [arXiv:0710.3820]. 
<br/>You are strongly recommended to read this summary when you 
start out to learn how to use PYTHIA 8.1. Note that some details 
have changed since the 8.100 version described there. 
 
<p/> 
For the physics description we refer to the complete 
<br/><b>PYTHIA 6.4 Physics and Manual</b> 
<br/>T. Sj&ouml;strand, S. Mrenna and P. Skands, JHEP05 (2006) 026, 
<br/>which in detail describes the physics (largely) implemented also in 
PYTHIA 8, and also provides a more extensive bibliography than found 
here. 
 
<p/> 
When you use PYTHIA 8.1, you should therefore cite both, e.g. like 
<br/><b>T. Sj&ouml;strand, S. Mrenna and P. Skands, JHEP05 (2006) 026, 
Comput. Phys. Comm. 178 (2008) 852</b>. 
 
<p/> 
Furthermore, a separate 
<br/><a href="worksheet.pdf" target="page"> 
<b>PYTHIA 8 Worksheet</b></a>, 
<br/>also an attached PDF file, offers a practical introduction to 
using the generator. It has been developed for and used at a few 
summer schools, with minor variations, but is also suited for 
self-study. 
 
<h2>Authors</h2> 
 
<p/> 
<b>Torbj&ouml;rn Sj&ouml;strand</b><br/> 
Department of Astronomy and Theoretical Physics, Lund University, 
S&ouml;lvegatan 14A, SE-223 62 Lund, Sweden<br/> 
phone: + 46 - 46 - 222 48 16, e-mail: torbjorn@thep.lu.se 
 
<p/> 
<b>Jesper Roy Christiansen</b><br/> 
Department of Astronomy and Theoretical Physics, Lund University, 
S&ouml;lvegatan 14A, SE-223 62 Lund, Sweden<br/> 
e-mail: Jesper.Roy.Christiansen@thep.lu.se 
 
<p/> 
<b>Nishita Desai</b><br/> 
Institut f&uuml;r Theoretische Physik, Universit&auml;t Heidelberg, 
Philosophenweg 16, D-69120 Heidelberg, Germany<br/> 
phone: +49 - 6221 54 9424, e-mail: Nishita.Desai@cern.ch 
 
<p/> 
<b>Philip Ilten</b><br/> 
Massachusetts Institute of Technology, 
stationed at CERN, CH-1211 Geneva 23, Switzerland<br/> 
e-mail: philten@cern.ch 
 
<p/> 
<b>Stephen Mrenna</b><br/> 
Computing Division, Simulations Group, 
Fermi National Accelerator Laboratory, 
MS 234, Batavia, IL 60510, USA<br/> 
phone: + 1 - 630 - 840 - 2556, e-mail: mrenna@fnal.gov 
 
<p/> 
<b>Stefan Prestel</b><br/> 
Theory Group, DESY, Notkestrasse 85, D-22607 Hamburg, Germany<br/> 
phone: + 49 - 40 - 8998-4250, e-mail: stefan.prestel@thep.lu.se 
 
<p/> 
<b>Peter Skands</b><br/> 
Theoretical Physics, CERN, CH-1211 Geneva 23, Switzerland<br/> 
phone: + 41 - 22 - 767 2447, e-mail: peter.skands@cern.ch 
 
<h2>Former authors</h2> 
 
<p/><b>Stefan Ask</b>, e-mail: ask.stefan@gmail.com 
 
<p/><b>Richard Corke</b>, e-mail: r.corke@errno.net 
 
<h2>Further contributions</h2> 
 
Makefiles, configure scripts and HepMC interface by <b>Mikhail Kirsanov</b>. 
<br/>Conversion of XML files to PHP ones by <b>Ben Lloyd</b>. 
<br/>Simple Makefile for Win32/NMAKE by <b>Bertrand Bellenot</b>. 
<br/>Extended Higgs sector partly implemented by <b>Marc Montull</b>. 
<br/>Parts of charm and bottom decay tables courtesy <b>DELPHI</b> and 
<b>LHCb</b> collaborations. 
<br/>Tunes and comparisons with data, based on Rivet and Professor, 
by <b>Hendrik Hoeth</b>. 
<br/>Text and code on the use of ROOT in conjunction with PYTHIA 
by <b>Rene Brun</b>, <b>Andreas Morsch</b> and <b>Axel Naumann</b>. 
<br/>Code and data for MRST/MSTW PDFs by <b>Robert Thorne</b> and 
<b>Graeme Watt</b>. 
<br/>Code and data for the CTEQ/CT PDFs by <b>Joey Huston</b> 
and colleagues. 
<br/>Help with implementing new proton PDFs by <b>Tomas Kasemets</b>. 
<br/>Code and data for Pomeron PDFs by <b>H1</b> collaboration and 
especially <b>Paul Newman</b>. 
<br/>Help with implementing new Pomeron fluxes and PDFs by 
<b>Sparsh Navin</b>. 
<br/>The new Hidden Valley code developed together with <b>Lisa Carloni</b>. 
<br/>Code for a Kaluza-Klein electroweak gauge boson provided by 
<b>Noam Hod</b> and <b>Mark Sutton</b>. 
<br/>Code for equivalent photon flux around an unresolved proton by 
<b>Oystein Alvestad</b>. 
<br/>The MBR diffractive model and central diffraction by 
<b>Robert Ciesielski</b>. 
<br/>2012 branching ratios for most light hadrons, and the tau lepton, 
by <b>Anil Pratap Singh</b>. 
<br/>The pythia8-config script has been contributed by 
<b>Andy Buckley</b>, along with many other helpful suggestions. 
<br/>Code and data for several of the NNPDF2.3 QCD+QED sets provided by 
<b>Juan Rojo</b> and <b>Stefano Carrazza</b>. 
<br/>The fjcore code from FastJet provided by <b>Matteo Cacciari</b>, 
<b>Gavin Salam</b> and <b>Gregory Soyez</b>. 
 
<br/><b>Note</b>: in several cases modifications have been made to 
the original code, in order to integrate it with PYTHIA. In these cases 
the blame for any mistakes has to rest with the regular authors. 
 
<h2>Licence</h2> 
 
PYTHIA 8 is licensed under the 
<a href="COPYING" target="page"><b>GNU General Public Licence 
version 2</b></a>. 
<br/>Please respect the 
<a href="GUIDELINES" target="page"><b>MCnet Guidelines</b></a> 
for Event Generator Authors and Users. 
 
<p/> 
The program and the documentation is 
Copyright &copy; 2014 Torbj&ouml;rn Sj&ouml;strand 
  
 
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