Measuring Coalescence Radii and Flow Using Identified Protons and Deuterons from Na44

Transverse mass spectra of protons and deuterons in rapidity window y=1.9{2.3 are presented for 158 A GeV Pb+Pb and 200 A GeV S+S and S+Pb collisions. The inverse slope parameter increases with system size and with particle mass. In the framework of a coalescence model a radius parameter RG can be extracted. Transverse mass dependence of RG is consistent with the 1= p mT decrease of the radius parameter as measured by HBT and thus provides an evidence for the radial ow. The Focussing Spectrometer, NA44, measures particle correlations and single particle distributions of charged hadrons with an excellent momentum resolution of p=p = 0:2%. A broad region in phase space is scanned by operating the spectrometer at two diierent angular settings and by choosing a nominal momentum setting of 4, 6 or 8 GeV/c. The transverse momentum coverage is 0 p T 1.6 GeV/c near central rapidity. A Cherenkov beam counter with a time resolution of 35 ps 1] gives the start time information. An interaction and centrality trigger is provided by a plastic scintillator counter covering the pseudo-rapidity range of approximately 1:3 3:5. The magnetic arm of the spectrometer consists of 2 dipole magnets and 3 super-conducting quadrupoles. The momentum range, p, is 20% of the nominal momentum setting. Tracks through the spectrometer are reconstructed with 3 wire chambers with pad and strip cathode readout (200m) and 3 hodoscopes with an average time of ight resolution of 100 ps. Two threshold Cherenkov counters are used to veto electrons and pions. This analysis compares deuterons from the 8 GeV/c momentum setting to protons from the 4 GeV/c setting at the same velocity. The rapidity range of the data is 1:9 y 2:3. The centrality trigger selects 8.7, 10.7 and 27% of the events with the highest multiplicity for S+S, S+Pb and Pb+Pb collisions, respectively. No further selection on higher centrality was performed. The beam was provided by the CERN SPS accelerator at an energy of 200 A GeV for the sulphur and 158 A GeV for the lead beam. The contamination of the data samples by other particle types has been estimated to be less than 2:5%.