Novel technique to access the strong interaction in three-body systems and Re-evaluated cosmic ray antinuclei fluxes

Two studies have been performed in this thesis: the measurement of strong interaction in three-body systems using the femtoscopy technique, and the estimations of cosmic ray antinuclei fluxes resulting from collisions between ordinary cosmic rays and the interstellar medium. In the past decade, the femtoscopy technique has been utilized to measure hadronic interactions between particles that were previously difficult to access through experiments, including hadron pairs with multi-strangeness or charm. The distances between particles in pp collisions at the LHC are of the order of 1 fm providing perfect conditions to measure the strong interaction. The natural next step is to extend this technique to the three-hadron case. Three-baryon interactions, especially p-p-p and p-p-$\Lambda$, are of great interest to nuclear and astrophysics, as they provide relevant input to better understand (hyper-)nuclei and the equation of state of dense systems. The latter is required to solve the hyperon puzzle, which aims to answer the question of which constituents make up the inner core of neutron stars. This thesis presents the first measurements of three-baryon correlations in non-bound systems. To achieve this goal, the femtoscopic technique was extended for the first time to the three-baryon case. The correlation functions of p-p-p and p-p-$\Lambda$ were studied in high-multiplicity pp collisions at $\sqrt{s}$ = 13 TeV, which were recorded with the ALICE detector at the LHC. The genuine three-body effects were studied using the Kubo's cumulant technique. A negative three-particle cumulant was measured for p-p-p triplets. The p-value extracted from the $\chi^2$ test corresponds to a deviation of 6.7$\sigma$ from the assumption that only two-body correlations are present in the system. It was evaluated in the kinematic region corresponding to the low relative momenta of three particles in center-of-mass system, at values of the hypermomentum $Q_3 < 0.4$ GeV/$c$. This result indicates the presence of genuine three-body effects. The measured p-p-p correlation function was also compared to the first preliminary calculations, which suggest that the observed cumulant is partially related to the antisymmetrization of the three-particle wave function. For thep-p-$\Lambda$ system, a positive cumulant was observed at low $Q_3$. The deviation from zero at $Q_3 < 0.4$ GeV/$c$ is 0.8 $\sigma$, suggesting that the data can be sufficiently well explained by assuming only two-body correlations in the system, within the current uncertainties. More conclusive results for both p-p-p and p-p-$\Lambda$ systems require a larger data sample, which is expected from the Run 3 data taking. To ensure that all events which include a collimated triplet are stored, a three-body software trigger was developed in this thesis. Cosmic ray antinuclei fluxes are an important channel for indirect dark matter searches. Some dark matter models, such as weakly interacting massive particles, are expected to annihilate into ordinary matter, including antinuclei. The produced antinuclei then propagate in the Galaxy and can reach detectors at Earth. Measuring cosmic ray antinuclei also includes a background component stemming from ordinary cosmic ray collisions with interstellar medium. Nevertheless, the fluxes from different origins are expected to have different energy distributions, leading to a signal-to-background ratio that can reach several orders of magnitude at low antinuclei energies. This thesis presents estimates of secondary cosmic ray antideuteron and antihelium-3 fluxes. The antinuclei source functions and inelastic cross-sections based on data-driven methods were implemented in GALPOP. The secondary antideuteron fluxes were studied in detail by employing different production models and propagation parameters to estimate relevant uncertainties in the field. The results showed that the dominant uncertainty at kinetic energies above 1 GeV/$A$ is due to production, as different production models provide significantly different results. In the lower energy regime, the choice of propagation parameters in GALPROP also contributes significantly to the flux uncertainty. The antideuteron inelastic cross section with matter, based on recent ALICE measurements, was implemented for the first time in GALPROP, and the experimental uncertainty was propagated to the flux predictions. The results showed that this uncertainty is only 25% at low kinetic energies, constituting the smallest contribution to the total uncertainty. The obtained results were also used to estimate the Galaxy's transparency to the propagation of secondary cosmic ray antideuterons. It was found to increase from around 35\% to 90\%, depending on the kinetic energy per nucleon. Similar studies were performed for the secondary cosmic ray antihelium-3 nuclei. The transparency increases from around 20\% to 90\% with increasing energy. The results show that the Galaxy is very transparent to the cosmic ray antinuclei and thus such fluxes could indeed be measured by the dedicated detectors in the future. Additionally, the secondary fluxes obtained from this thesis were compared to those expected from dark matter annihilation, revealing a signal-to-background ratio of several orders of magnitude for both cosmic ray antideuterons and antihelium-3 if a dark matter mass assumption of $m_{\chi}$ = 100 GeV is made.