Helicity-flip bremsstrahlung and the measurement of CP-violating form factors in polarized e+e- collisions.

Certain momentum correlations in the production and subsequent decay of heavy fermion pairs in e+e− collisions have increased sensitivity to CP-violating electric and “weak” dipole form factors of the fermion in the presence of longitudinal polarization of the e+e− beams. However, unless the polarizations of e+ and e are equal and opposite, collinear initial-state radiation accompanied by helicity flip results in a CP-invariant contribution to these and acts as a background, and must be calculated and subtracted in order to isolate the CP-violating contribution due to the dipole form factor. We calculate this background contribution to such correlations, to order α, in e+e− → τ+τ− and e+e− → tt̄. For the anticitipated luminosities at τ -charm factories and SLC, for the τ , and at a future linear collider with centre-of-mass energy of 500 GeV for the top, these backgrounds are smaller than the statistical background and may be safely neglected.