On the determination of the impact parameter from particle multiplicity measurements in heavy-ion collisions.

The event-by-event determination of the impact parameter from particle multiplicity emitted in heavy-ion collisions is considered. The associate problem of the determination of the particle multiplicity on both multi-event and event-by-event basis is formulated and discussed. It is shown that a multi-event data analysis procedure allows an accurate determination of the multipolicity distribution of the emitted particles even with not necessarily large total efficiency and granularity detection systems. In the event-by-event data analysis procedure a fold-to-multiplicity conversion based on the Bayes strategy is adopted. It is shown that a reliable event-by-event multiplicity determination and multiplicity resolution definition cannot prescind from a multi-event analysis of the full data set. It is found that the resolution of the event-by-event fold-to-multiplicity conversion procedure depends on the characteristics of the detection system, but not exclusively. The dependence on the particular multiplicity distribution investigated is discussed. It is concluded that event-by-event high-resolution impact parameter measurements can only be performed with very efficient and granular detection systems, but a gross event classification into central and peripheral collisions can be performed even with detection efficiency as low as Ω=0.3. [ABSTRACT FROM AUTHOR]