Direct Evidence for the Bose-Einstein Effect in Inclusive Two-Particle Reaction Correlations

Two-particle correlations are studied as a function of ${t}_{12}$, the square of the difference of the four-momentum of the particles. We observe that the ${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}$ correlation differs from the ${\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ correlation only at low values of ${t}_{12}$. This difference can quantitatively be understood as a consequence of Bose-Einstein statistics.