Transverse beam polarization and limits on leptoquark couplings in e+e- --> t tbar

It is shown that if electron and positron beams at a linear collider are transversely polarized, azimuthal asymmetries of the final-state top quark in e+e- --> t tbar can be used to probe a combination of couplings of left and right chiralities in a scalar leptoquark model. The CP-conserving azimuthal asymmetry would be a sensitive test of the chirality violating couplings. A linear collider operating at sqrt{s}=500 GeV and having transverse polarizations of 80% and 60% respectively for the e- and e+ beams, can put a limit of the order of 0.025 on the product of the left and right chirality leptoquark couplings (in units of the electromagnetic coupling constant), with a leptoquark mass of 1 TeV and for an integrated luminosity of 500 inverse fb. The CP-violating azimuthal asymmetry, which would provide a direct test of CP-violating phases in leptoquark couplings, can be constrained to the same level of accuracy. However, this limit is uninteresting in view of the much better indirect limit from the electric dipole moment of the electron.Comment: 13 pages latex, with 6 figures included. Revised version corrects minor error. Latest version corrects minor errors, to appear in Phys. Lett.

Helicity-Flip Bremsstrahlung and the Measurement of CP-Violating Form Factors in Polarized e+e−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 $\alpha$, in $e^+e^-\rightarrow \tau^+\tau^-$ and $e^+e^-\rightarrow t\bar{t}$. 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.Comment: 21 pages plain LaTeX, to be run twic

Electric dipole moment of top quark and CP-violating asymmetries in gamma gamma -> t tbar

CP-violating asymmetries due to a possible electric dipole interaction of the top quark in the production and subsequent decay of top quark-top antiquark pair in photon-photon collisions are studied. The asymmetries defined can be used to determine the imaginary part of the electric dipole form factors. A gamma-gamma collider with photon beams generated from laser back-scattering off electron beams with an integrated geometric luminosity of 20 fb^{-1} can put a limit of the order of 10^{-17} e cm on the imaginary part of the electric dipole form factor of the top quark if the electron beams have longitudinal polarization and the laser beams have circular polarization.Comment: 17 pages, LaTeX, 3 figures in postscript files (included), macros file include

Inclusive spin-momentum analysis and new physics at a polarized electron-positron collider

We consider the momentum distribution and the polarization of an inclusive heavy fermion in a process assumed to arise from standard-model (SM) $s$-channel exchange of a virtual $\gamma$ or $Z$ with a further contribution from physics beyond the standard model involving $s$-channel exchanges. The interference of the new physics amplitude with the SM $\gamma$ or $Z$ exchange amplitude is expressed entirely in terms of the space-time signature of such new physics. Transverse as well as longitudinal polarizations of the electron and positron beams are taken into account. Similarly, we consider the cases of the polarization of the observed final-state fermion along longitudinal and two transverse spin-quantization axes which are required for a full reconstruction of the spin dependence of the process. We show how these model-independent distributions can be used to deduce some general properties of the nature of the interaction and some of their properties in prior work which made use of spin-momentum correlations.Comment: 32 pages, plain latex, 3 figures produced by axodraw2, 4 tables, sequels to prior publications hep-ph/0601199 and arXiv:0805.2279; v2 corresponds to version accepted for publication in European Physical Journal C, compared to v1, extended discussions, additional figure, clarifying comments, additional reference