Source dynamics from deuterons and anti-deuterons in sqrt(s_NN) = 200 GeV Au+Au collisions

Abstract

We have studied the source dynamics of the matter in ultra relativistic $Au+Au$ collisions at $sqrt{s_{N N}} = $200 GeV by analyzing the production of the simplest nuclei: deuterons and anti-deuterons. In relativistic heavy ion collision the system expands and cool s, and when the interactions among the particles finally cease during the ``free ze-out", light nuclei like $d$ and $ar{d}$ can be formed. The transverse momentum ($p_T$) spectra of $d$ and $ar{d}$ in the range 1.1 $< $ $p_{T}$ $<$ 5.0 GeV/c have been measured at mid-rapidity. The slopes of the ha dron spectra are directly related to the temperature of the source at freeze-out and the flow velocity of the collectively expanding system. The radial flow has the effect of flattening the spectra of heavier particles, thus the $d$ and $ ar{d}$ spectra are less steeply falling than the (anti-)proton spectra. Measurements of radial flow velocity and freeze-out temperature using the blast- wave hydrodynamic model for deuterons was attempted. Our results indicate that w ithin this model the deuterons do not freeze-out contemporaneously with the prod uced hadrons. The deuteron spectra require a lower flow velocity than the proton spectra. Due to their unique sensitivity to the dynamics of the emission proces s, these results can constrain full hydrodynamics calculations. The coalescence probability, $B_2$, of neutrons and protons into deuterons as a function of transverse momentum and centrality has been studied. We observed a d ecrease in $B_2$ for more central collisions where the volume of the system is l arger. The ratio of the hadron spectra in central and peripheral collisions ($R_ {CP}$) is used to study the effects of the quark-gluon plasma medium on the prop agation of fast partons through it. For deuterons, we observe a significant enha ncement in $R_{CP}$ compared to other hadrons. This behavior indicates that both proton and neutron production are enhanced contrary to the suppression of pions .