Speaker
Dr
Huang Bingchu
(Brookhaven National Lab)
Description
Di-leptons serve as clean and bulk penetrating probes to study
the properties of the strongly interacting hot and dense medium
created in heavy ion collisions. They are produced in all stages
of the heavy-ion collisions and are not affected by strong
interactions, hence can probe the entire evolution of the
collision. Di-lepton production in the low mass range
($M_{ll}<1.1$ GeV/$c^{2}$) allows the study of vector meson
in-medium properties, an observable possibly connected to chiral
symmetry restoration. In the intermediate mass region
($1.1<M_{ll}<3.0$ GeV/$c^{2}$), di-lepton measurements serve as
a tool to extract the medium thermal radiation, which provides
direct information on the temperature of the early system.
Quantitative studies on these properties require systematic
measurements of di-lepton production yields as well as elliptic
flow as a function of invariant mass and transverse momentum
($p_T$). An extension of these studies to energy and centrality
dependent measurements offer crucial information on how the
system properties evolve with collision energies and system
sizes. The STAR experiment, with its large and full azimuthal
acceptance, clean electron identification over a wide momentum
range and low material environment, is very well suited to carry
out systematic studies on di-lepton production. In the years
2010 and 2011, more than one billion events were taken in 200
GeV Au+Au collisions and several hundred million events were
recorded at lower energies by the STAR experiment. In this
presentation, results from di-electron mass spectra as a
function of $p_T$ and centrality as well as the dependence of
elliptic flow on invariant mass in 200 GeV Au+Au collisions will
be presented. The results on mass, width, dN/dy, $p_{T}$ spectra
of $\omega$ and $\phi$ mesons will be reported. The first STAR
results of di-electron mass spectra and $p_T$ distributions at
midrapidity for Au+Au collisions at $\sqrt{s_{NN}}$ = 19.6, 39
and 62.4 GeV will be presented. These distributions will be
compared to model calculations of in-medium vector and thermal
radiation contributions to infer medium properties.
Author
Dr
Huang Bingchu
(Brookhaven National Lab)
