A fundamental symmetry of nuclear and particle physics is isospin whose third component is the Gell-Mann/Nishijima expression IZ=Q-(B+S)/2. The role of isospin symmetry in relativistic heavy-ion collisions is studied. An isospin IZ, strangeness S correlation is shown to be a direct and simple measure of flavor correlations, vanishing in a Qg phase of uncorrelated flavors in both symmetric N=Z and asymmetric N≠Z systems. By contrast, in a hadron phase, a IZ/S correlation exists as long as the electrostatic charge chemical potential μQ≠0 as in N≠Z asymmetric systems. A parallel is drawn with a Zeeman effect which breaks a spin degeneracy.
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