Study of multi-strange baryon production with ALICE at the LHC energies

This thesis reports on the measurement of the multi-strange baryon production in lead-lead (Pb-Pb) and proton-proton (pp) collisions at the centre-of-mass energy of 2.76 TeV per nucleon pair using the ALICE detector. The cascade identification technique, based on the topological reconstruction of weak decays into charged particles only is very effective thanks to the excellent particle identification and tracking capability of the ALICE central barrel detectors. The comparison of the transverse momentum (p$_T$) spectra for the $\Xi^{-}$ and $\Omega^{-}$ (and corresponding anti-particle) in Pb-Pb collisions with expectations from recent hydro models confirms the importance of an hydrodynamical approach in the description of the created system evolution. In addition, recent PYTHIA tunes results to underestimate the yields for the cascades in pp collisions. The measurements of the strangeness enhancement, one of the predicted signatures of the QGP formation, for the $\Xi$ and $\Omega$ at the LHC energy have been presented and compared with those at lower energies, showing similar characteristics to the ones observed at SPS and RHIC and also consistent with the picture of enhanced $s$$\bar{s}$ pair production in a hot and dense partonic (deconfined) medium. The historical role of the strangeness enhancement measurement within the context of the QGP study has been emphasized, focusing on the role of the canonical suppression mechanism for the strangeness production in the proton-proton system as the main explanation of the observed energy dependence of the strangeness enhancement. Finally, the nuclear modification factors for the $\Xi$ and $\Omega$ have been calculated in five centrality classes and compared with the corresponding factors for lighter particles measured by the ALICE Collaboration. The $\Xi$ seems to follow the same behaviour of the protons at high p$_T$ to indicate that progenitor partons of the two baryons show similar energy loss, while the $\Omega$ seems to be strongly affected by the strangeness enhancement, showing an R$_AA$ larger than unity. At mid-p$_T$, indications of mass-ordering between the different baryons (and mesons) are present. The higher p$_T$ reach for all the particles compared to the spectra at RHIC and the nuclear modification factor for the $\Omega$, not even measured at lower energies, make these preliminary results uniquely interesting as constraints for the various energy loss models.