Speaker
Mr
Md Nasim
(NISER, Bhubaneswar, India)
Description
One of the major goals of the heavy-ion experiments is to study the properties of hot and dense matter
created in the collision of two heavy
nuclei. Elliptic flow ($v_{2}$) of $\phi$ meson in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV has provided a clear evidence for partonic collectivity[1]. This was possible because of the small hadronic interaction cross section and early freeze-out for $\phi$ mesons[2]. On the other hand hadrons like protons (with similar mass as $\phi$ meson) have significantly large hadronic interaction cross section and freeze-out late. Therefore, comparison between $v_{2}$ of $\phi$ meson and proton
will be useful to understand the dynamical evolution of the hot and dense media created in such collisions.
In order to study the QCD phase structure, RHIC has conducted the beam energy scan program since 2010. In this talk, we report the measurement of $p_{T}$ integrated $v_{2}$ of $\phi$
mesons as a function of center of mass energy from 7.7 GeV to 200 GeV
to demonstrate the decrease in partonic contribution to collectivity
with the decrease in $\sqrt{s_{NN}}$. We compare the $\phi$-meson
$v_{2}$ to the corresponding values for protons. At high collision
energies, $\sqrt{s_{NN}}$ $>$ 27 GeV for example, we observe similar
values for the integrated $v_{2}$ for both protons and $\phi$ meson. At lower energies, $\sqrt{s_{NN}}$ $<$ 19.6 GeV, however, $\phi$-meson $v_{2}$ become much smaller, indicating that hadronic interactions become dominant in the energy region.
Further we compare to
transport model calculations with and without partonic interactions to emphasize our
conclusions. In addition, the effect of hadronic re-scattering on $v_{2}(p_{T})$ will be shown by
comparing $v_{2}(p_{T})$ of $\phi$ and proton. The study of re-scattering
effect on $v_{2}$ will be further corroborated by using various
models like those based on Hydro+Cascade and Transport approach.
References
[1] B. I. Abelev $\it$ et al. (STAR Collaboration), Phys. Rev. Lett. $\textbf{99}$, 112301 (2007).
[2] A. Shor, Phys. Rev. Lett. $\textbf{54}$,
1122 (1985); J. Adams $\it$ et al. (STAR Collaboration), Nucl. Phys. $\textbf{A 757}$, 102 (2005);
Md. Nasim, B. Mohanty and N. Xu, Phys. Rev. $\textbf{C 87}$, 014903 (2013).
Author
Mr
Md Nasim
(NISER, Bhubaneswar, India)
Co-authors
Dr
Bedangadas Mohanty
(NISER, Bhubaneswar, India)
Dr
Nu Xu
(LBNL, Berkeley, USA and CCNU, Wuhan, China)
Dr
Shusu Shi
(LBNL, Berkeley, USA)
