Strangeness enhancement in high multiplicity proton-proton collisions at $\sqrt{s}=7$ TeV with the ALICE detector at the LHC

ALICE is one of the seven experiments at the Large Hadron Collider (LHC) at CERN, dedicated to the physics of heavy-ion collisions and, in particular, the properties of the Quark Gluon Plasma (QGP). In addition to studying Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=2.76$\ TeV, ALICE has an extensive proton-proton (p-p) programme ($\sqrt{s}= 0.9$,\ 2.76,\ 7\ and 8\ TeV) aimed to provide a base for comparison with the Pb-Pb data as well as to complement the research in areas where ALICE is competitive with the other LHC experiments.\\* Of particular interest for the ALICE collaboration are the high-multiplicity p-p events. As suggested by the Bjorken formula for the initial energy density in high energy collisions, such events could create conditions comparable to those in heavy-ion collisions at RHIC where the formation of the QGP has been observed.\\* The identified charged hadron spectra in p-p collisions at $\sqrt{s} = 7$ TeV have been measured as a function of the event multiplicity, looking for signs of strangeness enhancement as one of the established signatures for the QGP formation. The analysis entails processing a sample of $\sim 80$\ M minimum-bias and $\sim 5$\ M high-multiplicity triggered p-p events. Three different particle identification techniques have been developed and assessed for the purpose of measuring the pion, kaon and proton yields over a momentum range of 0.2 GeV/$c \le p_{\rm{T}} \le 2.5$ GeV/$c$. A study of the systematic effects and the results are presented, including $p_{\rm{T}}$ spectra and integrated yields for pions, kaons and protons, K$^\pm/\pi^\pm$ and p$^\pm/\pi^\pm$ ratios as a function of multiplicity, and a comparison to recent models. No significant variation in the particle ratios is observed up to multiplicities of the order of $\mathrm{d}N_{\rm{ch}}/\rm{d}\eta \approx 42$.