Centrality determination for pPb data 2013

Centrality is very important for defining the collision system size in heavy ion collisions. It provides a tool for selecting events in a similar way in different experiments and facilitates the comparison of experimental results and theoretical calculations. The progress of centrality determination in pPb collisions at CMS is presented. The choice of variables used for event classification will be discussed. The method for the estimation of geometric quantities, such as the number of nucleon participants and nucleon-nucleon collisions will be shown. Note bene (22/01/2014): we now use the convention for p and Pb directions agreed upon with ATLAS and ALICE, according to which the proton beam goes in the direction of positive pseudorapidity.