Introduction

This project simulates the generation and decay of elementary particles following collisions of subatomic objects. In particular, among pions, kaons, protons and electrons, K* particles are generated. While the first ones are stable, the last one rapidly decays in equal proportions into a positive kaon and a negative pion, or a negative kaon and a positive pion.

The aim of the program is to detect the K* decay from the distributions of invariant masses of all particles. In particular, since the decay of K* produces pions and kaons of opposite charge, by analysing the distribution of invariant masses of all possible couples of particles with same charge and the distribution of invariant masses of all possible couples of particles with opposite charge, one can subtract the second from the first one and retrieve the distribution of invariant masses the distribution of invariant masses of all couples of particles generated by the decay. The same reasoning is repeated considering only pions and kaons in order to get more precise data.

Particles are generated in predefined proportions, with momentum distributed according to an exponential distribution and polar and azimuthal angle according to uniform distributions.

main_gen.C ( main.cpp if you prefer to compile not in root environment ) simulates the generation of subatomic particles and k*'s decay, and additionally shows useful distributions. All data regarding the simulated event are saved in a root file in order to be analysed later.

analize_histo.C, instead, is a ROOT macro that analyses the data acquired, prints statistics on terminal and draws useful histograms and fits. This macro must be run after after the simulation has been completed.

This project relies on ROOT Data Analysis Framework developed by CERN. Installing root is required in order to execute the simulation and the analysis macro. Code is written in C++ and uses root libraries to create histograms and analyze data.

To get more information about the project, please read the report relazione.pdf.

Compilation

The program can be compiled in two different ways. It can be done either externally using gcc compiler, or internally in the ROOT environment, which is recommended to make the program faster.
Type the following commands:

• External compilation

    user@user:~$ g++ -Wall -Wextra -o decay.exe particleType.cpp resonanceType.cpp particle.cpp main.cpp `root-config --cflags --libs`
    user@user:~$ ./decay.exe

• Internal compilation in root environment (recommended)

    user@user:~$ root
    user@user:~$ .L particleType.cxx+
    user@user:~$ .L resonanceType.cxx+
    user@user:~$ .L particle.cxx+
    user@user:~$ .L main_gen.C+
    user@user:~$ main_gen()

Data analysis

To analyze the data collected during the simulation using root type the following commands:

  user@user:~$  root 
  user@user:~$ .L analyze_histos.C 
  user@user:~$ analyze_histos() 

Credits

Last but not least, the program has been developed by Matteo Mirabelli, Riccardo Pagnoni, Andrea Maria Varisano and Alberto Zaghini for Laboratiorio di Elettromagnetismo e Ottica, OOP and Root module.