Which Chiral Symmetry is Restored in High Temperature Quantum Chromodynamics?

Sigma models for the high temperature phase transition in quantum chromodynamics suggest that at high temperature the $\mathrm{SU}\left(N_f\right)\times \mathrm{SU}\left(N_f\right)$ chiral symmetry becomes exact, but the anomalous axial U(1) symmetry need not be restored. In numerical lattice simulations, traditional methods for detecting symmetry restoration have sought multiplets in the screening mass spectrum. However, these methods were imprecise and the results, so far, incomplete. With improved statistics and methodology, we are now able to offer evidence for a restoration of the $\mathrm{SU}\left(2\right)\times \mathrm{SU}\left(2\right)$ chiral symmetry just above the crossover, but not of the axial U(1) chiral symmetry.