Kinematic Probes

As was seen in section 1.3 thermodynamic properties can be extracted from the collision observables. Usually, the temperature $T$, entropy density $s$, and energy density $\epsilon$ are identified with the average transverse momentum $\< p_T \>$, the hadron rapidity distribution $dN/dy$, and the transverse energy $dE_T/dy$, respectively [4]:

$$T \leftrightarrow \< p_T \> \hspace{2cm} s \leftrightarrow \frac{dN}{dy} \hspace{2cm} \epsilon \leftrightarrow \frac{dE_T}{dy}$$

A first order QGP phase transition is revealed in a plot of $T$ as a function of $\epsilon$. Such a plot would yield a rise, a plateau, and a second rise, due to the saturation of $T$ during the mixed phase.

However, the measured momentum distribution of hadrons does not reflect the conditions at the early stages of the collision, and is often influenced by a collective flow of particles.