Jet shape modification in Pb-Pb collisions at √S[sub]N[sub]N= 2.76 TeV using two-particle correlations

Abstract

This thesis focuses on two separate topics. The first topic concerns the upgrade of the Time Projection Chamber (TPC) detector of the ALICE experiment. The upgrade will take place during the second Long Shutdown (2019-2020). The part of the upgrade I participated in was the replacement of the detector’s current readout electronics with Gas Electron Multiplier (GEM) foils. This change would allow for the continuous readout of the data, resulting in a hundredfold increase in the amount of data the ALICE experiment can process, as the TPC is the central tracking detector. I was involved in the Quality Assurance (QA) of these GEM foils. The advanced QA procedure consists of three measurements, a long-term high-voltage measurement, a direct gain measurement and an optical scan. I have developed a graphical software to aid the QA of the optical and the high-voltage part, and that program is used in both advanced QA centers. I also developed software for the gain measurement of the foils, and carried out a correlation study between the GEM foil’s optical parameters and its gain [1]. The second topic is the analysis of the ALICE data, the measurement of the jet shape modification as a function of pseudorapidity in √sNN = 2.76 TeV Pb–Pb and pp collisions. In Pb–Pb collisions, the quark gluon plasma (QGP) is created, while in pp collisions, it provides only weak hints for its existence at very high multiplicity events (see e.g. Ref. [2]). Comparing results from these two collisions thus sheds light on the behavior of the new phase of the strongly interacting matter. I have carried out a two-particle correlation analysis, developed the analysis software, and performed the systematic error analysis. The results are also compared to AMPT simulations, as well as a custom Monte Carlo simulation. The structure of the thesis is therefore dissected into three distinct parts. In Part I a broad introduction preludes the two main topics, chapter 1 provides the physics background for the ALICE data analysis of Part III, while chapter 2 details the experimental layout that is necessary to appreciate the detector upgrade presented in Part II. Part II starts with the description of the TPC detector in chapter 3, and continues with the introduction of the GEM foils in chapter 4. The QA procedures of the GEMs are presented in chapter 5, which then streams into the correlation study between the GEM’s hole diameters and gain in chapter 6. It also covers the establishment of the QA criteria for the foils. Part III starts with a literature overview of the analysis topic in chapter 7, then describes the cuts applied to the data in chapter 8. It then discusses the method of the analysis in chapter 9. Corrections (chapter 10) and the evaluation of the systematic uncertainties (chapter 11) follow, before presenting the results of the jet shape analysis and conclude in chapter 12. The thesis closes with a complete summary.