Pythia 8 Event Production Electron positron distribution A basic analysis

Program Flow Initializaion. The event loop. Finishing.

Initialization - normal usage Already at the top of the main program file, you need to include the proper header file #include "Pythia.h" using namespace Pythia8; The first step is to create a generator object, e.g. with Pythia pythia;

Event Loop Inside the event generation loop you generate the next event using the next() method, pythia.next(); The generated event is now stored in the event object For instance, an event can be listed with pythia.event.list(), the identity of the i'th particle is given by pythia.event[i].id(), and so on.particle

Finishing At the end of the generation process, you can call pythia.statistics(); to get some run statistics, on cross sections and the number of errors and warnings encountered And cout<< your histograms

Histogramming As a first step you need to declare a histogram, with name, title, number of bins and x range (from, to). Hist elect("electron multiplicity", 100, -0.5, 799.5); Hist::Hist(string title, int numberOfBins, double xMin, double xMax) declare and define a histogram, where argument title : is a string with the title of the histogram at output, argument numberOfBins : is the number of bin the x range will be subdivided into, argument xMin : is the lower edge of the histogram, argument xMax : is the upper edge of the histogram.

Output format The key feature is that the Contents and Low edge have to be read vertically. For instance, the first bin has the contents 3 * 10^2 + 4 * 10^1 + 7 * 10^0 = 347. Correspondingly, the other bins have contents 179, 123, 207 and 283. The first bin stretches from -(1 * 10^1 + 0 * 10^0) = - 10 to the beginning of the second bin, at -(0 * 10^1 + 5 * 10^0) = -5. The visual representation above the contents give a simple impression of the shape. An X means that the contents are filled up to this level, a digit in the topmost row the fraction to which the last level is filled. So the 9 of the first column indicates this bin is filled 9/10 of the way from 3.00*10^2 = 300 to 3.50*10^2 = 350, i.e. somewhere close to 345, or more precisely in the range to

Example program