Speaker
Dr
Alexander Schmah
(Lawrence Berkeley National Lab)
Description
The main goal of the RHIC Beam Energy Scan (BES) is the exploration
of the QCD phase diagram in the region of a possible phase
transition between the Quark Gluon Plasma (QGP) and the hadron gas
phase. In the year 2010 the first part of the BES program was
successfully accomplished by recording data from Au+Au collisions
at $\sqrt{s_{NN}}=$ 7.7, 11.5 and 39 GeV. The second harmonic
($v_2$) of the azimuthal particle distribution relative to the reaction plane
was found to be one of the most important observables to
study the underlying dynamics in the early stage of the collisions.
The number-of-constituent quark (NCQ) scaling of $v_{2}$ is
interpreted as a signature of deconfinement and existence of the QGP phase.
At the lower energies studied it was expected to see a change in this
scaling behaviour as the role of the QGP phase should diminish.
We present $v_{2}$ measurements at all three beam energies for
identified hadrons ($\pi$, $K$, K$_{s}^{0}$, p, $\phi$, $\Lambda$,
$\Xi$) and light nuclei (d and $^{3}He$) as a function of $p_{T}$ for
various collision centralities. The measured nuclei $v_{2}$ are
compared to the proton $v_{2}$ and results from a dynamical coalescence
model calculation, while the NCQ scaling is tested using all identified hadrons.
For the first time, a significant difference in $v_{2}$ between baryons and
anti-baryons is observed. The difference increases
with decreasing center-of-mass energy.
Author
Dr
Alexander Schmah
(Lawrence Berkeley National Lab)
