The V0 detector provides the basic, so called minimum-bias, trigger in ALICE. The measured time of arrival of the charged particles at the surface of the detector is used in order to discriminate parasitic collisions of the beam with the remaining gas in the LHC beam-pipe.
The V0 detector is the default collision centrality estimator in ALICE. Heavy nuclei are extended objects and collisions between them do not always happen at the centre. The centrality is obtained by summing up the energy deposited in the two disks of the V0 detector. This observable scales directy with the number of primary particles generated in the collision and therefore to the centrality.
The detector participates in the measurement of the charged particle multiplicity density and the orientation of the reaction plane in collisions of heavy ions