Final State Interactions in Bose-Einstein Correlations

We are presenting here the new formulae for Bose-Einstein correlations (BEC) which contain effects of final state interactions (FSI) of both strong (in $s$-wave) and electromagnetic origin. We demonstrate the importance of FSI in BEC by analysing data for $e^{+}{e}^{-}$ annihilation and for heavy collisions. The inclusion of FSI results in the practical elimination (at least in $e^{+}{e}^{-}$ data) of the so called degree of coherence parameter $\lambda$ (which becomes equal unity) and the long range parameter $\gamma$ (which is now equal zero).