Observation of partial U_A(1) restoration from two-pion bose-einstein correlations

The effective intercept parameter of the two-pion Bose-Einstein correlation function, λ_*, is found to be sensitive to the partial restoration of U_A(1) symmetry in ultra-relativistic nuclear collisions. An increase in the yield of the η’ meson, proposed earlier as a signal of partial U_A(1) restoration, is shown to create a “hole” in the low p_t region of λ_*. A comparison with NA44 data and central S + Pb collisions at 200A GeV is made, and implications for future heavy ion experiments are discussed.