Study of the resolution on the track impact parameter in ALICE

Abstract
The impact parameter of a track is defined as the distance of closest approach of the track to the interaction vertex. The two projections of the impact parameter, in the transverse plane and along the beam direction, are usually considered separately. The measurement of the impact parameter is crucial for the study 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. In ALICE, the information on the impact parameter is given by the Inner Tracking System, and, in particular, by the Silicon Pixel Detectors, which have very fine granularity and are positioned very close to the interaction point. This note presents a systematic study of the dependence of the impact parameter resolution on particle kinematics and particle type, on event multiplicity and on the thickness of the pixel detectors.