H. Ohnishi et al., MULTIPLICITY DEPENDENCE OF PION SOURCE SIZE IN HEAVY-ION COLLISIONS, Progress of theoretical physics. Supplement, (129), 1997, pp. 161-165
HBT interferometry is a well known technique to study the space-time e
xtent of the particle source in heavy ion collisions. The NA44 experim
ent measures one and two particle spectra of identified pions, kaons a
nd protons around mid-rapidity produced in heavy ion collision at the
CERN SPS. We present the relation between charged multiplicity density
and the HBT radius parameters in S + Pb collisions at 200 A GeV and P
b + Pb collisions at 158 A GeV. The HBT radius parameter increases as
a function of charged multiplicity density in Pb + Pb collisions in a
similar way to that found previously in S + Pb collisions. We will dis
cuss what are can learn about the condition at freeze-out using these
experimental results.