Light fragment yields from central Au+Au collisions at $11.5A\hspace{0.5em}\mathrm{GeV}/c$

Inclusive double differential multiplicities of deuterons, ${}^3\mathrm{H},$ ${}^3\mathrm{He},$ and ${}^4\mathrm{He}$ measured by E877 for $11.5A\hspace{0.5em}\mathrm{GeV}/c$ Au+Au collisions at the Brookhaven’s Alternating Gradient Synchrotron (AGS) are presented. Light fragments at beam rapidity are measured for the first time at AGS energies. Beam rapidity deuteron and ${}^4\mathrm{He}$ yields and transverse slope parameters are found to be strongly dependent on the impact parameter, and the shape of the deuteron spectra is not consistent with that expected for a simple thermal distribution. The deuteron yields relative to proton yields are analyzed in terms of a simple coalescence model. While results indicate an increase in source size compared to collisions of lighter systems at the same energy, they are inconsistent with a simple coalescence model reflected by a rapidity dependence of the coalescence parameter $B_d.$ A new approach utilizing an expanding thermalized source combined with a coalescence code is developed for studying deuteron formation in heavy-ion collisions. The strong dependence of deuteron yields on collective motion implies that deuteron yields relative to those of protons can be used for constraining source parameters.