CERN Accelerating science

Ultrarelativistic heavy-ion collisions in experimental facilities are conducted to investigate the dynamics of strongly interacting matter. These laboratories produce a dense soup of deconfined quarks and gluons called the quark-gluon plasma (QGP). The ALICE experiment at the LHC is dedicated to studying this exotic state of matter that probes its formation from the aftermath of heavy-ion collisions. Heavy quarks (charm and beauty) are interesting probes to examine the QGP medium. Because of their large masses, they produce at the initial stages of the collision and get to traverse the entire evolution of the medium. Their production mechanisms in proton--proton (pp) collisions are of great interest, providing stringent tests to perturbative quantum chromodynamic (pQCD) calculations. Interestingly, heavy-quark production is also correlated to event properties. Studies have shown a strong correlation between charm production and the event multiplicity in pp collision, where a significant role of multiparton interactions is suspected. The role of auto-correlation effects between charm production and multiplicity is also weighed in. Moreover, with identifiable QGP signatures in high multiplicity pp collisions, the participation of charm in collective-like effects is also worth investigating. In addition, with event shapes, charm production can be categorized into the hard and soft components that allow unfolding of the production mechanisms with event activity. This thesis outlines the studies performed in charm production via D-meson production as a function of event-multiplicity and -shapes in pp collisions at $\sqrt{s} = $ 13 TeV. $$ $$ The second focus of this thesis is on light nuclei ($\mathrm{d,~^{3}H,~^{3}He}$) production in collision experiments. Light nuclei are clusters of nucleons that survive temperatures of $\mathcal{O}(100~\mathrm{MeV})$ in heavy-ion collisions, orders higher than its binding energy. Understanding their $`$puzzling' production mechanism is a contentious topic in the community, with the coalescence of nucleons being one of the popular phenomenological models. It is based on the overlap principle between the nucleon phase-space distribution and the nuclei probability distribution. The nucleon phase space generally relies upon an event generator, to which coalescence is appended in an afterburner mode. The coalescence model is initially designed with a box nuclei distribution prescription, which is studied on $\mathrm{d,~^{3}H,~^{3}He}$ production in RHIC and LHC energies. The model is revamped with the nuclei's Wigner distribution, inspired by its quantum mechanical wavefunction. With this update, finer details can be added in terms of a common nucleon emission source. This connects the nucleon-nucleon (NN) interactions during the inception of the light cluster formation in these collision experiments. Furthermore, investigation with strong, Coulombic and quantum statistical corrections will capture the femtoscopic details in these NN interactions. This thesis includes all the stages of developing an $`$in-situ' coalescence model discussed above and its implementation.