Abstract
We study deuteron production using no-coalescence hydrodynamic + transport simulations of central AuAu collisions at $\sqrt{s_{NN}} = 7 - 200$ GeV. Deuterons are sampled thermally at the transition from hydrodynamics to transport, and interact in transport dominantly via $\pi p n \leftrightarrow \pi d$ reactions. The measured proton, Lambda, and deuteron transverse momentum spectra and yields are reproduced well for all collision energies considered. We further provide a possible explanation for the measured minimum in the energy dependence of the coalescence parameter, $B_2(\sqrt{s_{NN}})$ as well as for the difference between $B_2(d)$ for deuterons and that for anti-deuterons, $B_2(\bar{d})$.
Highlights
Heavy-ion collisions are often called “Little Bang” due to a rapid expansion, cooling, and a sequence of freezeouts reminiscent of the evolution of the early Universe.Another common feature of the Little and Big Bangs is nucleosynthesis, or production of light nuclei
In relativistic heavy-ion collisions, this reaction does not have sufficient time to create the observed amount of deuterons, which follows from its small cross section and the typical time of collision, ≈10−23–10−22 s
We have previously suggested that the pion catalysis reaction deuteron production at π√psnN N↔=π2d76p0laGyseVtheindtohme imnaindtrarpoildeitiyn region [1,2]
Summary
Heavy-ion collisions are often called “Little Bang” due to a rapid expansion, cooling, and a sequence of freezeouts reminiscent of the evolution of the early Universe. For hadrons the chemical freeze-out temperature, TCFO, which is determined from hadron yields, is larger than the kinetic temperature TKFO which is extracted from the momentum spectra, TCFO > TKFO This picture is supported by the fact that the yield-changing reactions typically have smaller cross sections, so they cease earlier during the expansion of the fireball. Deuteron yields and spectra are consistent with the same TCFO and TKFO for nuclei as for hadrons [19] This means that they have to be colliding with other particles between chemical and kinetic freeze-out. In coalescence the spatial extent of the deuteron wave function relative to the size of colliding system matters, while in the thermal model it does not Despite these differences, we are able to accommodate the core ideas of both thermal and coalescence models in our dynamical simulation in the following way: We use relativistic hydrodynamics to simulate the locally equilibrated fireball evolution until the chemical freeze-out. Hadronic transport is applied at the later stage of collision, when the fireball is dilute enough so that mean-free paths of the particles are larger than their Compton wavelengths
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