Multiplicity Selection Studies in pp, p-Pb and Pb-Pb collisions in ALICE

In late 1970's, first indications of a dense, expanding medium, produced in heavy-ion (AA) collisions, were reported by J.~Gosset~{\em et al.}~\cite{PlasticBall} and several other authors~\cite{CollectiveExpansion}. Ever since then, these observations have been under a profound investigation, until more than a decade ago it has been established by SPS: a new state of matter, the so-called quark gluon plasma (QGP), is created in heavy ion collisions. When produced, this medium is so hot and dense, that its constituents -- quarks and gluons -- though still strongly coupled, barely interact with each other and hence become the degrees of freedom of the medium (effect known as {\em asymptotic freedom}). Naturally, such a hot and dense matter has an extremely short life-time before it cools down and expands, exhibiting a collective movement of particles, also refered to as {\em flow}. While the presence of flow in AA collisions has been confirmed and is a subject of research, recent results from proton-nucleus (pA) and proton-proton (pp) collisions seem to indicate the presence of a flowing medium as well~\cite{Kisiel, Werner}. The observation of collective behaviour in a QCD medium in pp and pA collisions is a rather unexpected result and hence has to be checked thoroughly before being confirmed. In the following analysis, current centrality selection procedures will be investigated to find, whether the observed flow-like behaviour can be introduced by chosing fixed pseudorapidity, $\eta$ cuts in the multiplicity estimator.