Analysis techniques for femtoscopy and correlation studies in small collision systems and their applications to the investigation of p–Λ and Λ–Λ interactions with ALICE

Femtoscopy is a technique relating the correlations between pairs of particles to their emission source and interaction potential. Traditionally femtoscopy is used to study the properties of the emission source, mostly by using charged pion correlations, for which the correlation function is determined only by the Bose-Einstein statistics and Coulomb interaction. The topic of this work is the non-traditional baryon–baryon femtoscopy, the goal of which is to study the interaction potential between different baryon pairs, assuming the emission source is fixed. Such an approach is quite challenging as it requires an exact treatment of the strong potential in order to compute the correlation function, as well as knowledge on the profile and size of the emission source. In the work presented here, a new “Correlation Analysis Tool using the Schrödinger equation” (CATS) has been developed to tackle the issue related to the modeling of the correla- tion function. In previous works it was proposed that in small collision systems the source is approximately the same for all baryon–baryon pairs and this feature leads to the opportunity of using the p–p correlations to fix the source, allowing to study the interaction of other pairs. However, the limits of validity of this method were never quantitatively studied. In particular, the decays of short-lived resonances are expected to influence the emission source differently based on the particle species involved. In this work a new model was developed to handle this effect, making possible to perform non-traditional femtoscopy with much higher precision. This new analysis techniques and method developed were used by the ALICE col- laboration to study a multitude of different baryon–baryon systems, including p–Λ, p–Σ^0 , p–Ξ − , Λ–Λ, p–Ω^− and has even been applied to the meson sector to study the p–K^− interaction. Aside the development of CATS and the new source model, the author was the main analyzer of the p–Λ and Λ–Λ systems, therefore these results will be discussed in detail. In particular, the study of p–Λ has an important link to the equation of state of nuclear matter and the existence of massive neutron stars. In this work the chiral effective field theory computations are verified against the p–Λ data collected by the ALICE collaboration. The Λ–Λ system is of great theo- retical interest, as some models predict the existence of a bound state, the so called H-dibaryon, which could be composed of two Λs. The current work provides fur- ther experimental constraints on the Λ–Λ scattering parameters and binding energy of the hypothetical bound state.