Production of Light (anti-)Nuclei with E864 at the AGS

Light nuclei can be produced in the central reaction zone via coalescence in rel-ativistic heavy ion collisions. E864 at BNL has measured the production of ten stable light nuclei with nuclear number of A = 1 to A = 7 at rapidity y ≃ 1.9 and p T /A ≤ 300M eV /c. Data were taken with a Au beam of momentum of 11.5 A GeV /c on a Pb or Pt target with different experimental settings. The invariant yields show a striking exponential dependence on nuclear number over ten orders of magnitudes with a penalty factor of about 50 per additional nucleon. This penalty factor is used to estimate the strange quark matter (strangelet) production in the baryon rich and strangeness enhanced environment. The measurements of the pro-He) are presented as well. A model of local thermal equilibrium with radial flow at the kinetic freeze-out with a temperature of T = 112 ± 10M eV , chemical potential of µ B = 503 ± 20M eV and flow velocity of about V 2 ⊥ ≃ 0.5c seems to be able to describe the data in the gross scale with the exceptions of the production of antihyperons and hypernuclei. The large antihyperon production and the extra penalty for hypernuclei production are quite surprising. 1. Introduction Relativistic heavy ion collisions may create high energy density and high baryon density in the reaction zone. Light nuclei can be produced by the recombination of created or stopped nucleons [1]. This recombination process is called coalescence. Coalescence of nuclear clusters can be characterized by the penalty factor for a nucleon added to the nuclear cluster. This idea can be extended to hypernuclei to calculate the strangeness penalty factor. Both baryon and strangeness penalty factor are useful to estimate the production rate of strange quark matter in terms of coalescence or thermal production. Since the probability of coalescence of a particular nuclear system (d, 3 He, etc.) depends on the properties of the hadronic system formed as a result of the collision, the study of the coalescence process is useful in elucidating those properties. For example, in a coalescence model, the coalescence probability depends on the temperature, baryon chemical potential (essentially the baryon density), and the size of the system, as well as the statistical weight (degen-eracy) of the coalesced nucleus. The data reported shows evidence that the probability may also depend on the binding …