P. Poulose

CP-violating asymmetries in e+e− → tt with longitudinally polarized electrons

New CP-violating asymmetries of decay leptons in e+e− → tt, arising from electric and weak dipole couplings of tt to γ and Z, are examined in the case of unpolarized and longitudinally polarized electrons. The new asymmetries measured together with the old ones can help to determine independently the real and imaginary parts of the electric as well as weak dipole couplings. Longitudinal beam polarization, if present, obviates the need for the simultaneous measurement of more than one asymmetry, and enhances considerably the sensitivity to the CP-violating parameters. Numerical results are presented for the Next Linear Collider with s=500 GeV and ∫ L dt=10 fb−1.

Simple decay-lepton asymmetries in polarized e+e− → tt and CP-violating dipole couplings of the top quark

Abstract We study two simple CP -violating asymmetries of leptons coming from the decay of t and t in e + e − → t t , which do not need the full reconstruction of the t or t for their measurement. They can arise when the top quark possesses nonzero electric and weak dipole form factors in the couplings to the photon and Z , respectively. Together, these two asymmetries can help to determine the electric and weak dipole form factors independently. If longitudinal beam polarization is available, independent determination of form factors can be done by measuring only one of the asymmetries. We obtain estimates of 90% confidence limits that can be put on these form factors at a future linear e + e − collider operating at s = 500 GeV .

CP-violating dipole form factors of the top quark and tau lepton in scalar leptoquark models

We calculate the CP-violating electric and weak dipole form factors of the top quark and the tau lepton in models with scalar leptoquarks coupling only to the third generation of quarks and leptons. We obtain numerical values of the real and imaginary parts of these form factors at various energies for different values of leptoquark masses and couplings. The existing limits on the tau electric and weak dipole form factors allow us to put a limit on the masses and couplings of such leptoquarks and therefore on the top electric and weak dipole form factors. We also discuss constraints on the form factors coming from indirect limits on leptoquark masses and couplings deduced from LEP results on Z properties.