D*+ nuclear modification factor versus centrality in lead-lead collisions at sqrt(s_NN) = 2.76 TeV at ALICE

Abstract

From Quantum Chromodynamics it follows that at extremely high energies, quarks and gluons can be found in a deconfined state, called the Quark-Gluon Plasma (QGP). The ALICE detector at CERN was built to study lead-lead collisions at energies high enough to produce the QGP. In this thesis we study the production of D*+ mesons versus centrality in lead-lead collisions at sqrt(s_NN) = 2.76 TeV with the ALICE experiment at the Large Hadron Collider at CERN. With this study we will calculate the systematic uncertainty of the measurement. Also, we will determine the reconstruction efficiency of the detector. Then we can calculate the Nuclear Modification Factor RAA, which is the ratio of produced D mesons in Pb-Pb collisions compared to p-p collisions. Because particles lose energy in the dense QGP, we will measure less D mesons at high pT in Pb-Pb collisions. The actual RAA enables us to test the models which are used to predict the properties of the QGP.

Three detectors of the ALICE experiment are used for this study: the Inner Tracking System (ITS), the Time Projection Chamber (TPC) and the Time of Flight detector (TOF). We need those to reconstruct the D*+ and the D0 daughter from the measured particles. We then determined the raw yield in 2 pT ranges and 5 centrality bins. To determine the systematic uncertainty, we analyzed the stability of the yield when using different fitting functions and ranges, and also bin counting. The systematic error of the yield was approximately 3-6%, but varied with the centrality and pT. The efficiency turned out to be approximately 10%. Then calculating the RAA, we found it was approximately 0.2 for the most central collisions and was closer to unity for the more peripheral collisions.