It may happen that even though the T0 centrality trigger is present, the
spectrometer (primarily due to the azimuthal narrowness of its acceptance) gets
no reconstructable tracks, and the event is of no use for the analysis.
In the Pb beam period, the tracking device of the limiting acceptance is
the pad chamber.
For this reason, since 1995, we require a hit in the pad chamber along with at
least one hit slat in each of the scintillation hodoscopes H2 and H3
(
).
To analyze correlations among identical particles, NA44 triggers on double
track multiplicity.
In this work, by multiplicity trigger a requirement of at least a
single track is always meant.