الفهرس | Only 14 pages are availabe for public view |
Abstract In particle collisions such as proton-proton collisions, a number of very interesting phenomena have been observed, which are still not entirely understood. The observation of the heavy ion like ridge that observed in pp collisions suggests the need for a study of the correlations and thus also Bose-Einstein effects in high multiplicity pp collisions. Interesting phenomena have been observed in pp collisions already in 2011: an unexplained ridge structure was observed in two-particle correlations in angular difference, which created excitement in the field but was left until now unexplained. Intensity interferometry in particle physics is a direct and powerful experimental method to determine the shapes, sizes and lifetimes of the emitting sources of particles. In particular, boson interferometry which plays an important rule in investigating the space-time structure of particle production processes. Bose-Einstein correlations (BEC) between two identical bosons reflect both geometrical and dynamical properties of the particle emitting source. In this thesis we study Bose Einstein Correlations, i.e. measurements of the distance distribution of particles in the 4-vector momentum space. It will be of great interest to make such measurements in pp collisions and study the evolution of the ’source sizes’ of the interference regions as function of produced pair kinematics. The CMS experiment is especially well tailored for these kinds of measurements, since it has an excellent central tracker allowing make very precise measurements of the charged particles that leave the interaction region of the collision. We therefore make these measurements based on charged particles, i.e. basically study the charged pion correlations. This is the main topic of the thesis. In this thesis we study Bose-Einstein correlations in proton-proton at the highest energies available in the laboratory. The experimental data is collected with the Compact Muon Solenoid (CMS) detector located at the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) near Geneva, Switzerland. We investigated BEC for proton-proton colliding beams at 7 TeV centre-of-mass energy recorded at CMS in 2010, in addition to the 13 TeV centre-of-mass energy proton-proton collisions recorded in 2015. The minimum bias (MB) and high multiplicity (HM) events from both energies were used in our study. The first chapter of the current thesis introduces the historical and theoretical background of Bose-Einstein Correlations. It also explains the derivation of BEC correlation function and its parametrization. A brief introduction to the LHC collider and the structure of the CMS experiment and its sub-systems is introduced in the second chapter. The third chapter states the different data sets and MC simulations used in the present analysis, and explains the methods of event and track selections used in our analysis. It also contains the analysis of Bose Einstein Correlations and results of fitting the Bose- Einstein correlation function. The correlation function parameters are also studied as functions of both charged-particle multiplicity and mean-transverse momentum of the correlated pairs. |