CERN Accelerating science

High energy heavy-ion collisions provide us with the unique opportunity to study the Quark-Gluon Plasma (QGP) in a laboratory setting. The QGP is a special state of matter in which quarks and gluons, fundamental particles that compromise the nuclei of atoms, are deconfined, not bound into larger particles (hadrons). The QGP lasts for only a short time - on the order of $10^{-23}$ seconds - and therefore cannot be measured directly. However, a useful probe of the QGP is the beauty quark, which is created in the first moments of a heavy-ion collision and experiences the full evolution of the QGP. As they travel through the QGP, beauty quarks interact with the other partons (quarks and gluons) via elastic and inelastic scattering [gluon bremsstrahlung], produce quark and antiquark pairs, and lose energy. The beauty quarks later form larger bound states (like B mesons), which further decay into particles such as electrons before reaching detectors. In this thesis, electrons from beauty hadron decays (beauty-decay electrons) are measured in heavy ion collisions of lead-on-lead ions (Pb-Pb) at center-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV with the ALICE detector at the LHC. The analysis is conducted separately for collisions with 0-10% centrality (i.e.\ most ``head-on" collisions) and 30-50% centrality (i.e.\ slightly off-center collisions). The results will be compared with previous measurements of heavy-flavor (charm and beauty) decay electrons and with theoretical predictions.