Composition of spectator matter as a key to centrality determination

Europe/Zurich
CERN

CERN

Description

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Abstract:
It is common to assess the centrality of nucleus-nucleus collisions by measuring forward energy in  a hadronic calorimeter and relating it to the total volume of spectator matter in each event. However, in the case of restricted calorimeter acceptance, when, for example, only spectator neutrons are detected, it is difficult to distinguish between very central and very peripheral collisions. With our AAMCC model we calculate the composition of spectator matter, e.g., n/p ratio for forward nucleons, the number of charged fragments per spectator nucleon and other characteristics as functions of impact parameter b. We show that the relative contributions of explosive multifragmentation and sequential evaporative decays of spectator residues essentially depend on b. We conclude that the proposed characteristics can be used as centrality attributes to be measured with more advanced forward detectors.