CERN Accelerating science

Studies related to heavy-ion collisions at the most powerful particle accelerators in the world, the Large Hadron Collider (LHC) at CERN, Switzerland, and the Relativistic Heavy Ion Collider (RHIC) at BNL, USA, have primarily focused on the creation and properties of the primordial matter consisting quarks and gluons. This extremely dense and hot state of thermalized partons is also known as quark-gluon plasma (QGP). Due to the shorter lifetime of QGP, experiments rely on several indirect signatures that hint towards the formation of QGP in ultra-relativistic collisions of nuclear matter. While the formation of QGP has been established for a long time in heavy-ion collisions, its presence in small collision systems still needs to be determined. However, recent measurements of heavy-ion-like behavior in high-multiplicity pp collisions at the LHC have drawn the attention of the heavy-ion physics community. The appearance of ridge-like structures and the enhancement of strangeness add to these speculations. Increased production of strange hadrons can only be explained via forming a strongly interacting medium at thermal and chemical equilibrium. To determine whether the underlying physics processes involved in the strangeness production can also be probed with topological event selection instead of the average charged-particle multiplicity, a relatively new event shape classifier has been introduced at the LHC, known as the transverse spherocity ($S_0$). This event-shape observable can decouple the jet-dominated events from the events with spherical soft emission of particles. The first event is called the jetty type, and the latter is called the isotropic type. Jetty events result from enhanced contributions of perturbative QCD processes; however, isotropic events arise due to the interplay of several soft QCD processes, such as the multi-parton interactions and the initial and final state radiations. It is found that the production rates of strange particles are slightly higher for soft isotropic events and highly suppressed in hard jetty events. This supports the hypothesis that in high-multiplicity pp collisions, heavy-ion-like effects such as strangeness enhancement and radial flow are manifested in the isotropic events. Thus, transverse spherocity can separate events based on azimuthal topology and control heavy-ion-like effects in high-multiplicity pp collisions. A similar study of strange hadron production with topological event selection can also be performed for the case of charm hadrons. In the presence of QGP, the yield of charmonium ($c\bar{c}$) is suppressed compared to the yield in the non-QGP scenarios in hadronic collisions. Therefore, studies involving charm hadrons with different topological event selections can help us understand its production mechanism and constrain various phenomenological models. Additionally, it can help us understand the observed heavy-ion-like effects in isotropic events in high-multiplicity pp collisions at the LHC. With these motivations, this analysis measures the $p_{\rm T}$-differential yield of inclusive $J/\psi$ as a function of transverse spherocity in high-multiplicity pp collisions at $\sqrt{s} = 13$~TeV with ALICE. For this analysis, the reconstruction of $J/\psi$ is performed through the electromagnetic decay channel, $J/\psi \rightarrow \mu^{+}\mu^{-}$ , B.R.~=~($5.961 \pm 0.033)\%$ in forward rapidity, $2.5