Exploring the baryon correlation puzzle via multiplicity-dependent two-particle angular correlations in pp, p–Pb, and Pb–Pb collisions at the LHC energies

The fundamental queries surrounding the creation of one of the most abundant particles in the universe, protons, and the intricate mechanisms underlying the production of baryons remain largely unanswered, posing significant challenges in high-energy physics. This study fully investigates the angular correlations between pairs of particles to illuminate these mechanisms and improve our understanding of the underlying physical processes. 
The study of angular correlations is one of the most effective tools one has for that purpose, opening up the possibility of studying physical phenomena such as mini-jets, quantum statistics, and various conservation laws, which are themselves the basis of the baryon production mechanism and from which the complex interplay governing particle interactions in high-energy collisions is revealed. Each of these effects is a distinct correlation source and exhibits individual behavior in $\Delta\eta, \Delta\varphi$ space (where $\Delta\eta$ is the pseudorapidity difference and $\Delta\varphi$ is the azimuthal angle difference of two particles), which is why each pair particle correlation is unique. 

Recent experimental results of proton-proton collisions at the energy of $\sqrt{s}$ = 7 TeV have revealed an anticorrelation in particle distributions that poses a challenge to existing Monte Carlo models. This observation has led to the emergence of what is called the "baryon correlation puzzle". Although several studies have already been conducted, it remains an area for further exploration and understanding.
In this thesis, a new piece is added on the baryon correlation puzzle, analyzing the behavior of anticorrelation but also comparing with the correlation functions of mesons. Taking advantage of the advanced particle identification capabilities of the ALICE experiment at the Large Hadron Collider (LHC), a first study in ALICE of the angular correlation functions for pairs of particles, $\pi^{+}\pi^{+}+\pi^{-}\pi^{-}$, $\pi^{+}\pi^{-}$, K$^{+}$K$^{+}$+K$^{-}$K$^{-}$, K$^{+}$K$^{-}$, pp+$\bar{\rm{p}}\bar{\rm{p}}$, and p$\bar{\rm{p}}$ is done across different multiplicity classes and various collision systems: proton-proton (pp), proton--lead (p--Pb), and lead--lead (Pb--Pb) at LHC energies.

Previous results obtained in ALICE employed the probability ratio definition. However, this approach has limitations when applied to different multiplicity classes, mainly because of the underlying scaling factor of 1/N, where N represents the number of particles within each class. To isolate this effect, an alternative method is introduced using a rescaled two-particle correlation function, a concept originally proposed by the STAR collaboration.
By investigating angular correlations new insights into the underlying physics governing these particle interactions and the mechanisms of baryon production can be provided.
Although our analysis does not lead to definitive conclusions, it lays important groundwork for future investigations and encourages theorists to refine and improve existing models.