Multiple (multi-)strange hadron production in proton-proton collisions at $\sqrt{s}$ = 5.02 TeV with ALICE at the LHC

The increased production of strange hadrons in heavy-ion collisions compared to minimum-bias pp collisions has historically been interpreted as one of the earliest signatures of the formation of a deconfined quark-gluon plasma. One of the most significant findings from Run 1 and Run 2 of the LHC is the observation by the ALICE Collaboration of an enhanced production of (multi-)strange to non-strange hadron yields, gradually rising from low-multiplicity to high-multiplicity pp and p–Pb collisions, reaching values close to those measured in peripheral Pb–Pb collisions. Despite these observations, the origin of this phenomenon in small collision systems remains unclear. Furthermore, none of the current QCD-inspired Monte Carlo generators can quantitatively describe the observed behavior. This emphasizes the need for additional experimental data, new observables and theoretical advancements to uncover the microscopic mechanisms driving strangeness enhancement. A deeper understanding of the mechanisms behind strangeness production, and hadronization more in general, could be achieved by measuring the (multi-)strange particle multiplicity distribution (P($\textit{n}_{S}$)). A novel method involving event-by-event count-ing of strange particles offers a promising approach. In this thesis, the first ALICE results of the multiplicity distributions for K$^{0}_{S}$, $\Lambda$, $\overline{\Lambda}$, $\Xi^{-}$, $\overline{\Xi}^{+}$ , $\Omega^{-}$, and $\overline{\Omega}^{+}$ in pp collisions at $\sqrt{s}$ = 5.02 TeV are presented as a function of charged particle multiplicity. These results provide a unique perspective on the correlation between charged and strange particles' production. Furthermore, the measurement of P($\textit{n}_{S}$) enables the determination of the average yields of multiplets for each type of strange particle, widening the scope of strangeness production studies beyond average values and enabling the investigation of extreme cases where up to six strange quarks coalesce into hadrons in a single event. Additionally, by comparing hadron combinations with varying $u$ and $d$ quark compositions but identical total strange ($s$) quark content, it becomes possible to isolate the contributions to the enhancement pattern that arise from mechanisms unrelated to strangeness. These findings are compared with state-of-the-art phenomenological models implemented in commonly used Monte Carlo event generators, drastically enhancing the sensitivity to the different processes implemented in each approach. This thesis also provides an overview of the data quality of the MUon IDentifier (MID) during pp and Pb–Pb collisions in Run 3 (2022–2024), with a focus on monitoring the asynchronous quality control.