Helicity-Flip Bremsstrahlung and the Measurement of CP-Violating Form Factors in Polarized $e^{+}{e}^{-}$ Collisions

Abstract

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 $\alpha$, in $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}$ and $e^{+}{e}^{-}\to t\bar{t}$. For the anticitipated luminosities at $\tau$-charm factories and SLC, for the $\tau$, 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.

Comments: 21 pages plain LaTeX, to be run twice