Primary vertex in the ALICE experiment in absence of the event reconstruction

ALICE is a general-purpose apparatus for the study of ultra-relativistic heavy-ion collisions at the Large Hadron Collider of the CERN. The study of such reactions demands the determination of the primary vertex in three dimensions with good resolution. We have developed an algorithm for finding the vertex position even in absence of the event reconstruction. The performances of such an algorithm have been studied as a function of the vertex position, particle multiplicity and magnetic field.