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

Abstract

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 $\sqrt{sNN}$ = 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 ~ 80 M minimum-bias and ~ 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 $\leq$ pT $\leq$ 2.5 GeV /c. A study of the systematic effects and the results are presented, including pT 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 dN$_{ch}$/d$\eta$ $\approx$ 42