Minimum Bias Measurements with the ATLAS experiment at LHC: strangeness production and $\overline{\Lambda^{0}}$ to $\Lambda^{0}$ particle ratio

The understanding of the basic properties of minimum bias events at the LHC energies is the subject of this thesis. In particular the production of the $K^{0}_{s}$ meson, $\Lambda^{0}$ and $\bar{\Lambda^{0}}$ baryons using the first 190$\mu b^{−1}$ of proton-proton collision data collected with a Minimum Bias Trigger in the ATLAS experiment have been studied, showing the very good tracking performance of the Inner Detector already in the first period of data taking. Moreover a preliminary measurement of the $\bar{\Lambda^{0}}$ to $\Lambda^{0}$ production ratio versus pseudorapidity, rapidity and transverse momentum is presented. The importance of this measurement is related to the understanding of the transfer of baryon number from the beam to the relatively central rapidity range of the measured acceptance.