Mdhluli, Joyful Elma2024-02-012024-02-012024https://hdl.handle.net/10539/37489A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, School of Physics, University of the Witwatersrand, Johannesburg, 2023The differential heavy-flavour (charm and beauty quark) production as a function of the charged-particle multiplicity is investigated in pp collisions at √ s = 5.02 TeV. The heavy-quark production cross section as a function of transverse momentum (pT) and pseudorapidity (η) is also evaluated. The measurement of the inclusive yield of heavy quarks via the single-muon (µ) decay channel is done in the muon spectrometer at forward pseudorapidity (−4 < η < −2.5) and the charged-particle multiplicity using the Silicon Pixel Detector at central pseudorapidity (|η| < 1). These measurements are important in order to gain more insight into which processes are involved in the collision at a partonic level as well as provide information on the interplay between hard and soft mechanisms during particle production. Reference data taken during Run 2 in 2015 and 2017 in pp collisions at √ s = 5.02 TeV are analyzed for measurements of the inclusive heavy-flavour decay muon differential cross-section and heavy-flavour decay muon yield as a function of the charged-particle multiplicity. A total number of 102.7 M (21.34 M) events for the single muon low (high)- pT triggers are analyzed for both measurements. Minimum bias triggered events with multiplicity tracklets > 0 are used for multiplicity estimation. Two methodologies are utilized, the data-driven method and the ”Official Framework”. Results of inclusive heavy-flavour decay muon differential cross-section measured as a function of pT are compared with the theoretical model FONLL, the data and theoretical model are in agreement within systematic uncertainties. The results are also compared with measurements in pp collisions at √ s = 7 TeV, an energy dependence is observed. Results of inclusive heavy-flavour decay muon yield as a function of the charged-particle multiplicity indicated an approximately faster than linear correlation. Comparisons with other heavy-quark measurements vs charged-particle multiplicity is made and the measurements are in agreement at low charged-particle multiplicities. This thesis also reports on the Service Task work done. This entailed tests performed on detector elements of the Muon Chambers (MCH) that suffered high-voltage trips that were repaired during the long shutdown (LS2). The detector elements were successfully repaired and are currently stored as spares for the Run 3 data-taking period.enParticlesCollisionsThesis