Pion (non-) correlations in hadronic events at the Z resonance

Abstract

In this thesis, a study is presented of the interference, or Bose-Einstein correlation, of pions. Pions can be created in high energy electron-positron collisions, in so called hadronic events. In these events, most of the initial energy is transformed into pions. The exact mechanism of this conversion, the hadronization process, is not understood. One important parameter, the size of the region in which the hadronization takes place, can be accessed by studying Bose-Einstein correlations of identical pions. The hadronic events studied in this thesis were produced in electron-positron collisions in the LEP collider at CERN (Geneve, Switzerland). Both neutral and charged pions were identified and their properties were measured with the L3 detector. It is found that the (spherically shaped) region in which neutral pions appear has a radius of approximately 0.31 femtometre. For charged pions the radius is of the order of 0.46 femtometre. These results are not identical, which indicates a fundamental property of the hadronization process. Further study is required to precisely understand this difference