Pythia

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Notes for pythia paper

http://home.thep.lu.se/~torbjorn/Pythia.html

"The Pythia program is a standard tool for the generation of events in high-energy collisions between elementary particles, comprising a coherent set of physics models for the evolution from a few-body hard-scattering process to a complex multiparticle final state. Parts of the physics have been rigorously derived from theory, while other parts are based on phenomenological models, with parameters to be determined from data. Currently the largest user community can be found among the LHC experimentalists, but the program is also used for a multitude of other phenomenological or experimental studies."

"At the onset, all code was written in Fortran 77. Pythia 8.100 [11] was the first full release of a complete rewrite to C++." Precursor was Pythia 6

 Sjöstrand, Torbjörn, Jesper Roy Christiansen, and Nishita Desai. "PYTHIA." PYTHIA. 2014. Web. 02 Feb. 2016.

http://www.pantheon.org/articles/p/pythia.html

"The Pythia operated as a vehicle for Apollo's will to be known to those on earth. A believer would make a sacrifice and present a question to a male priest. The male priest would then present the question to the Pythia."

http://people.du.ac.in/~pmehta/FinalSem/Rockyfinal.pdf

"1. Initially two beam particles are coming in towards each other. Normally each particle is characterized by a set of parton distributions, which defines the partonic substructure in terms of flavour composition and energy sharing.

 2. One shower initiator parton from each beam starts off a sequence of branchings, such as q → qg, which build up an initial-state shower.

3. One incoming parton from each of the two showers enters the hard process, where then a number of outgoing partons are produced, usually two. It is the nature of this process that determines the main characteristics of the event.

4. The hard process may produce a set of short-lived resonances, like the Z 0 /W± gauge bosons, whose decay to normal partons has to be considered in close association with the hard process itself.

5. The outgoing partons may branch, just like the incoming did, to build up final-state showers.

6. In addition to the hard process considered above, further semihard interactions may occur between the other partons of two incoming hadrons.

7.When a shower initiator is taken out of a beam particle, a beam remnant is left behind. This remnant may have an internal structure, and a net colour charge that relates it to the rest of the final state.

8. The QCD confinement mechanism ensures that the outgoing quarks and gluons are not observable, but instead fragment to colour neutral hadrons."

http://arxiv.org/pdf/0710.3820v1.pdf

"The Pythia class is the main means of communication between the user and the event-generation process. We here present the key methods for the user to call, ordered by context. Firstly, at the top of the main program, the proper header file must be included: 9 #include "Pythia.h" To simplify typing, it also makes sense to declare using namespace Pythia8; Given this, the first step in the main program is to create a generator object, e.g. with Pythia pythia; In the following we will assume that the pythia object has been created with this name, but of course you are free to pick another one. When this object is declared, the Pythia constructor initialises all the default values for the Settings and the ParticleDataTable data bases. These data are now present in memory and can be modified in a number of ways before the generator is initialised (see below). Most conveniently, Pythia’s settings and parameters can be changed by the two methods pythia.readString(string); for changing a single variable, and pythia.readFile(fileName); for changing a set of variables, one per line in the input file. The allowed form for a string/line will be explained as we consider the databases in the next section. Further, methods will be introduced to list all or only the changed settings and particle data."