Open heavy-flavour production in high-energy proton-proton and nucleus-nucleus collisions at CERN-LHC energies

Abstract

The field of relativistic heavy-ion collisions focuses on the study of matter under extreme temperatures and/or densities. Understanding the predicted quark matter phase is a necessary step in understanding the origin of our Universe. Cross-section measurements in proton-proton collisions are, besides providing an important test for perturbative quantum chromodynamic calculations, essential as a baseline for the heavy-ion analyses. Furthermore, correlation observables hold great promise for the study of final-state radiation and the dynamical properties of the hot strongly interacting matter phase. This thesis consists of both parts: a measurement of the D*+ meson invariant production cross-section with the ALICE experiment and a theoretical model study using EPOS3+HQ on a new observable based on heavy-flavour correlations.

First of all, the D*+ meson production cross-section in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 5.02 TeV is reported. The D*+ meson is reconstructed in the exclusive hadronic decay channel using the invariant mass method: D*+ -> D0 pi+ -> K- pi+ pi+. The reconstruction was performed in the transverse momentum (pT) range 1-24 GeV/c, using 116 million minimum-bias events. A heavy-flavour enriched Monte-Carlo sample was used to compare the results and extract the reconstruction efficiencies. The pT-differential cross-sections are compared with Fixed Order plus Next-to-Leading Logarithm calculations. The overall production is well described, however, the data is on the higher side of the theoretical uncertainty band. The results were approved by the ALICE Collaboration as preliminary results for the Quark Matter conference in 2017.

The influence of final-state radiation of heavy quarks in high-energy proton-proton collisions is studied using a new proposed transverse momentum correlation observable. The transverse momentum correlation of D and Dbar mesons, which have been emitted with an azimuthal difference angle close to 180 degrees, is identified as an observable which is sensitive to the final-state radiation. This is demonstrated performing calculations with the event generator Pythia 6 and the EPOS3+HQ model. The initial symmetric pT = pT' correlation in proton-proton collisions is not completely vanished, neither for the final DDbar nor for the ccbar and bbbar before hadronisation. Also a difference in the shape of the distribution for EPOS3+HQ and Pythia 6 is found. The use of the new observable to differentiate between collisional and collisional+radiative in-medium energy loss mechanisms in Pb-Pb collisions is limited. Different centrality classes have been studied, but no significant difference in the distribution for both energy loss mechanisms was found. The work for this part of the thesis has been done during an internship for three months at Subatech in Nantes. The results of this theoretical study are presented in a paper, which will be submitted soon.