Production des baryons multi-étranges au LHC dans les collisions proton-proton avec l'expérience ALICE

Strange quarks define a valuable probe for the understanding of quantum chromodynamics. The present PhD work falls within this scope; it deals with the study of multi-strange baryons Ξ– (dss) and Ω– (sss) in proton-proton (pp) collisions at the LHC. The analyses make use of the ALICE experiment and are performed at central rapidities (y ≈ 0) and low transverse momentum (pT < 8,5 GeV/c). The production rates per event of these baryons are drawn from the measurement of differential spectra as a function of the hyperon momentum, d²N / dpTdy = f(pT). At √s = 0.9 TeV, the production for ( Ξ– + Ξ+ ) in the inelastic pp interactions is derived from a small statistics of events. At √s = 7 TeV, the large quantity of available data allows the measurement of production rates for each of the four species : Ξ–, Ξ+, Ω– and Ω+. At both energies, experimental data spectra are compared to spectra as produced by different benchmark phenomenological models (Pythia and Phojet). The comparison shows an unequivocal underestimate of the spectra by the Monte Carlo generators in their current versions (up to a factor ~4 for Ξ, ~15 for Ω). Furthermore, an analysis of azimuthal correlations (Ξ± - h±) is led at intermediate pT (2 < pT < 5 GeV/c) for the pp data at √s = 7 TeV. These correlations indicate that, when the momentum of Ξ± rises, the emission of the latter is preferentially done in correlation with jets.