The effective restoration of the chiral ${\mathrm{U}}_A\left(1\right)$ symmetry in strong interactions is studied using the linear chiral $\mathrm{SU}\left(3\right)\times \mathrm{SU}\left(3\right)$ model at finite temperatures. We find that the disappearance of the chiral anomaly causes a considerable change in the meson mass spectrum. We propose several signals for detecting this chiral phase in ultrarelativistic heavy-ion collisions: The $\eta /{\pi }^0$ ratio is enhanced by an order of magnitude, the $a_0$ is suppressed in the $K\overline{K}$ mass spectrum, and the scalar $\kappa$ meson appears as a peak just below the $K^{*}\left(892\right)$ in the invariant $\pi K$ mass spectrum.

• Received 15 June 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.3261