Source dynamics from deuterons and anti-deuterons in sqrt(s_NN) = 200 GeV Au+Au collisions
Valle, Hugo Edilberto
:
2008-12-22
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
.