Speaker
Description
Nature of QCD phase transitions in high energy collisions can be pinned down by studying the
behaviour of thermodynamic response functions with respect to $T$ and $\mu_B$.
A first order phase transition is signalled by the divergence of
specific heat ($c_v$), whereas for a second order
or continuous transition, isothermal compressibility
($k_T$) diverges.
$c_v$ is estimated at the kinetic freezeout hyper
surface (at $T_{\rm kin}$), whereas $k_T$ is at chemical freezeout
hyper surface (at $T_{\rm ch}$).
Thus simultaneous measurements of $c_v$ and $k_T$ as a
function of collision energy probes the exact nature of phase
transition and can pin down
the location of the Critical Point in the ($T$,$\mu_{B}$) plane.
The heat capacity is expressed as, $ C = \bigl( \frac{\partial E}{\partial T} \bigr)_{V}$, which implies $C^{-1} =
\frac{(\langle T_{\rm kin}^2 \rangle - \langle T_{\rm kin} \rangle ^2 )}
{ \langle T_{\rm kin} \rangle ^2}$. Thus $c_v$ can be experimentally probed through $\langle p_{\rm T} \rangle$ distribution.
Similarly, $k_T = \frac{1}{V} \bigl( \frac{\partial V}{\partial P} \bigr)$, which gives
$ k_T = \frac{\sigma_N^2}{N^2}\frac{V}{k_BT_{\rm ch}} $, where $N$ and $\sigma_N^2$
are the number of charged particles and its variance. Thus $k_T$ can be obtained through multiplicity fluctuation of charged particles.
$c_v$ and $k_T$ have been calculated from the mean
transverse momentum ($\langle p_{\rm T} \rangle$) and charged particle multiplicity
fluctuations, measured on an event-by-event
basis [1,2,3]. Experimental results along with results from the hadron
resonance gas (HRG) model and event generators will be presented.
(1) Sumit Basu, et al., Phys. Rev. C94, 034909 (2016).
(2) M. Mukherjee, et al., J. Phys. G: Nucl. Part. Phys. 43, 085102 (2016).
(3) M. Stephanov, et al., Phys. Rev. D60, 114028 (1999).
| Preferred Track | Correlations and Fluctuations |
|---|---|
| Collaboration | Not applicable |
