Energy and centrality dependence of deuteron and proton production in Pb+Pb collisions at relativistic energies -: art. no. 024902

The transverse mass m(t) distributions for deuterons and protons are measured in Pb+Pb reactions near midrapidity and in the range 0<m(t)-m< 1.0 (1.5) GeV/c(2) for minimum bias collisions at 158A GeV and for central collisions at 40 and 80 A GeV beam energies. The rapidity density dn/dy, inverse slope parameter T and mean transverse mass [m(t)] derived from m(t) distributions as well as the coalescence parameter B-2 are studied as a function of the incident energy and the collision centrality. The deuteron m(t) spectra are significantly harder than those of protons, especially in central collisions. The coalescence factor B-2 shows three systematic trends. First, it decreases strongly with increasing centrality reflecting an enlargement of the deuteron coalescence volume in central Pb+Pb collisions. Second, it increases with m,. Finally, B-2 shows an increase with decreasing incident beam energy even within the SPS energy range. The results are discussed and compared to the predictions of models that include the collective expansion of the source created in Pb+Pb collisions.