Signatures of the Tricritical Point in QCD

Abstract

Several approaches to QCD with two massless quarks at finite temperature T and baryon chemical potential mu suggest the existence of a tricritical point on the boundary of the phase with spontaneously broken chiral symmetry. In QCD with massive quarks there is then a critical point at the end of a first order transition line. We discuss possible experimental signatures of this point, which provide information about its location and properties. We propose a combination of event-by-event observables, including suppressed fluctuations in T and mu and, simultaneously, enhanced fluctuations in the multiplicity of soft pions.

Figures (2)

• Figure 1: The schematic phase diagram of QCD. The dashed lines represent the boundary of the phase with spontaneously broken chiral symmetry in QCD with 2 massless quarks. The point P is tricritical. The solid line with critical end-point E is the line of first order transitions in QCD with 2 quarks of small mass. The point M is the end-point of the nuclear liquid-gas transition probed in multifragmentation experiments. The superconducting phase of QCD bailincolorsuperconductorbergesraj, marked SC, is not relevant to our discussion.
• Figure 2: Schematic examples of three possible trajectories for three values of $x$ on the phase diagram of QCD (see. Fig. \ref{['fig:pd']}). The points I, S, H and F on different trajectories are marked with different symbols. The dashed lines show the locations of the initial, I, and final, F, points as $x$ is increased in the direction shown by the arrows.