Production of strangeness in partonic interactions at the LHC

Sammanfattning: The strong interaction is responsible for nearly all observable baryonic matter in the Universe. Quantum Chromodynamics, which describes interactions between quarks and gluons, however, cannot be solved analytically in the non-perturbative regime, involving low momentum transfers. In this regime, interesting phenomena occur, such as the formation of colour-neutral hadrons from constituent quarks and in extreme conditions, the transition of hadronic matter to a plasma of deconfined quarks and gluons. This quark-gluon plasma (QGP) is believed to have comprised the Universe in the first several microseconds after the Big Bang and can be recreated in laboratory conditions, such as in collisions of ultra-relativistic heavy nuclei at the Large Hadron Collider (LHC).The QGP exhibits certain signatures whose strength varies with the multiplicity of particles produced in the collisions, which is directly linked to the number of colliding nucleons in the collision and the energy density in the initial state. In the last decade, contrary to expectations, it has been discovered that pp collisions and pA collisions also exhibit QGP-like behaviour, including an increase in the production of strange particles and an increase in the ratio of neutral strange hadrons, Lambda to K0s, at intermediate transverse momentum p_T. However, in pp collisions, it is challenging to link particle multiplicity to the initial state.This dissertation aims to investigate the origin of QGP-like behaviour in pp collisions by analysing the production of K0s and Lambda particles and their dependence on event shape and sub-structure. Specifically, measurements are performed using the ALICE detector at the LHC for pp collisions at $\sqrt{s}=13$ TeV. For the first time ever, observables quantifying the event shape geometry, the transverse spherocity S_O, and the magnitude of the underlying event activity, the R_T, R_T,min, and R_T,max, are employed to investigate their effect on the production of K0s and Lambda particles. These observables allow for a more differentiated understanding of the collision dynamics and help access the number of colliding quarks and gluons (partons). The results of this study will contribute to the understanding of the QGP-like behaviour in pp collisions and help further the understanding of the strong interaction at low momentum transfers.