Interaction vertex reconstruction in pp collisions at LHC with ALICE
The knowledge of the position of the interaction vertex is used not only to
reconstruct primary tracks in the Inner Tracking System (ITS), but it is
also crucial for the measurement of the physics signals characterized
by the presence of a secondary vertex with a small displacement.
This is, in particular, the case for the detection of particles with
open charm and open beauty, namely D^0 (c\tau\simeq 123 micron),
D^+ (c\tau\simeq 315 micron) and B mesons (c\tau\sim micron).
We discuss how, for the proton-proton runs, the position
of the interaction vertex will have to be measured for each event,
not only along the beam direction (as in Pb-Pb), but also in the
transverse plane. We present a complete strategy to
accomplish this task.