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One of the main goals of the Relativistic Heavy Ion Collider (RHIC) at the
Brookhaven National Laboratory and the Large Hadron Collider (LHC) at CERN, is to
find the signature of the Quark-Gluon Plasma (QGP) and exploring the QCD phase
diagram to find out the QCD Critical Point. RHIC started the Beam Energy Scan (BES)
program to map the QCD phase diagram to hunt for the QCD Critical Point. Presently,
the location of the critical point, a distinctive feature of the phase diagram, is beyond
the reach of the theoreticians, while experimentally it may be possible to locate it by
varying the center of mass energy of heavy ion collisions. RHIC has measured
different observables to look for the signature of the formation of QGP. The higher-
order moments of the net-particle multiplicity of the conserved quantities have been
measured to locate the QCD critical point.
In this talk, we will discuss experimental findings from RHIC and from the LHC which
indicate the existence of a hot and dense medium. We will also discuss the
measurements of the various moments, such as mean, standard deviation (σ ),
skewness (S) and kurtosis (κ) of the net-kaon and net-proton multiplicity distributions
at mid-rapidity in Au + Au collisions from √s NN = 7.7 to 200 GeV with the STAR
experiment at RHIC. This work has been done with the aim to locate the critical point
on the QCD phase diagram. These moments and their products are related to the
thermodynamic susceptibilities of conserved quantities such as net baryon number,
net charge, and net strangeness as well as to the correlation length of the system
which diverges in an ideal infinite thermodynamic system at the critical point. For a
finite system, existing for a finite time, a non-monotonic behaviour of these variables
would indicate the presence of the critical point. Furthermore, we will also discuss the
volume independent moment products Sσ, κσ 2 of net-kaon and net-proton multiplicity
distributions as a function of collision centrality and energy. The results have been
compared to theoretical models, which do not include a CP and the implications of the
observation to CP physics will be discussed. |