$\Lambda/\rm K^0_s$ associated with a jet in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV measured with the ALICE detector

In high energy heavy ion collisions, the QCD matter undergoes a phase transition to a hot and dense strongly coupled Quark Gluon Plasma, where quarks and gluons are deconfined in a volume of nuclear dimensions. At intermediate pT, 2<pT<8 GeV/c, a decoupling from pure hydrodynamical flow is observed, most noticeable in central collisions, demonstrated by the peak in the ratio of baryons to mesons, e.g. the Lambda/K0s ratio, compared to measurements in pp collisions. At high pT (>10 GeV/c), the particle production is dominated by jet fragmentation, where it is understood that these jets have suffered large energy losses propagating through the dense QGP. The goal of this thesis is to experimentally investigate the baryon-to-meson anomaly at intermediate pT, and to determine its origin, i.e. if it is an effect arising from the soft, collective, part (the bulk) of the medium, or from the hard processes (modified jet fragmentation). This will be done by analyzing central Pb-Pb collisions at sqrt(s_NN)=2.76 TeV from the ALICE experiment recorded in the 2011 heavy ion run period. For this analysis, a novel two-particle correlation technique called the eta-reflection method is developed, where a separation can be made of the contributions from Lambda and K0s particles produced in the soft underlying events from those which are produced in association with a high-pT trigger particle, representing a jet-like environment. The aim of this analysis is to separate the hadron production associated with the jet from that of the bulk, and to measure the Lambda/K0s ratio at intermediate pT in the bulk and jet-like environment, to see how the baryon-to-meson anomaly differs in the two regions. The results show that at intermediate pT the hadron formation is dominated by the expanding and cooling Quark Gluon Plasma, giving rise to the anomalous overabundance of Lambda over K0s which characterizes the inclusive results. The production of K0s and Lambda associated with a high-pT trigger particle (presumably a leading hadron in a jet) is quite similar to that observed in pp collisions, i.e. unaffected by the processes in the dense, colored medium.