$\Lambda, \overline{\Lambda}$ and $K^{0}_{S}$ Production in In-In and In-Si Collisions at 158 GeV/nucleon

This thesis presents results on $\Lambda$ and K0 S production in In-In and In-Si collisions at 158 GeV per nucleon at the NA60 experiment at the CERN SPS. It shows the methods used to reconstruct the decays of the studied particles, which include strict data selection cuts to improve the signal to background ratio enough for them to be visible, as well as the subsequent background subtraction techniques. The necessary acceptance and efficiency corrections and their calculations are described, and transverse momentum and rapidity spectra presented for both particles. The transverse momentum distributions were found to be consistent with a scenario of collective flow affecting the temperature in a mass dependent way. No significant changes are seen in the T inverse pT slope parameter with collision centrality. The K0 S rapidity distribution is peaked at mid-rapidity and was well represented by a gaussian. The $K^{0}_{S}$ rapidity distribution, however, is flat at mid-rapidity with a drop in yield at 3.5–4 units of rapidity. This is consistent with the superposition of the two main $\Lambda$ production methods: associated production and baryon/anti-baryon pair production. An attempt was made to measure the $\overline{\Lambda}\Lambda$ ratio, which was found to be in agreement with previous measurements of this quantity in Pb-Pb collisions at 158 GeV per nucleon.