Reconstruction of virtual photons from Au+Au collisions at 1.23 GeV/u

• Main Author: Harabasz, Szymon
• Format: Others
• Language: en
• Published: 2017
• Online Access: https://tuprints.ulb.tu-darmstadt.de/6605/1/HarabaszSzymon_thesis_tuprints_allembed_2.pdf; Harabasz, Szymon <http://tuprints.ulb.tu-darmstadt.de/view/person/Harabasz=3ASzymon=3A=3A.html> (2017): Reconstruction of virtual photons from Au+Au collisions at 1.23 GeV/u.Darmstadt, Technische Universität, [Ph.D. Thesis]

This thesis presents data analysis of dilepton excess radiation in Au+Au at beam kinetic energy 1.23A GeV experiment performed by HADES. It starts with an overview of QCD symmetries and its thermodynamics properties. It is followed by a discussion of details of experimental setup that are necessary to understand the data analysis. The data analysis itself is described in the main part of the manuscript. This starts with tools and techniques that have been used. An excellent performance of lepton identification with a neural network, in terms of lepton sample purity, has been proven. It is not possible to divide all e+ and e− in a single event into correlated pairs and combinatorial background must be estimated on a statistical way. Reconstructed signal should be corrected for efficiency in order to be compared with other measurements and theory predictions. This is done by multiplying the signal after background subtraction by a factor depending on the same pair kinematic variable as the signal spectrum. After all the analysis steps spectra are examined in order to make physical statements. Average temperature of the medium emitting dileptons was directly extracted from the fit to the invariant mass. Comparison to model calculations showed their consistency with the data in various observables.