Effects of Fsi, Cr and Bec at Small Relative Momenta of Particles and W-mass Systematics at Lep

The observation of the enhanced production of like–sign particle pairs by LEP experiments at Z does not insure that the observed correlations owe their origin to Bose-Einstein correlations(BEC). They could, for example, arise from final state interactions(FSI) between pions with small relative momenta. (we recommend not to call BEC and/or Colour Reconnection as ’FSI effects’ as it is generally used). It turns out that it is possible to discount the possibility of visible FSI effects by virtue of the smaller correlations between unlike-sign particles, which could arise from final state interaction effects too. As was shown at LEP, the unlike-sign particle configurations show also a correlations. The like-sign pions necessarily are in an isospin I=2 state and the unlike-sign pions are dominantly in the isospin I=0 state. The scattering length for I=2 is more than a factor three smaller than the one for I=0. This insures that the FSI effects for like-sign pion pairs are expected to be nearly an order of magnitude smaller than those observed in unlike-sign pions. Even if one would attribute all the correlations observed for unlike-sign pions to final state effects, then essentially none of