Test of CP-invariance in e+e−→Z0→τ+τ− and a limit on the weak dipole moment of the τ lepton

Top-quark production in hadron-hadron collisions and anomalous top-quark–gluon couplings

“…This is an observable of the tensor type T ij introduced in [32] and used in search for CP violation in the decay Z → τ + τ − [33]. In [12] the expectation value ofÔ L was calculated for m t = 130 GeV keeping only terms of zeroth and first order ind …”

Dipole moments of theτlepton as a sensitive probe for physics beyond the standard model

“…The method of optimal variables is different from the idea originally proposed by Bernreuther et al which consisted of measuring CP odd tensor correlations [7] amongst the charged final state particles in the reaction e + e − → τ + + τ − → X +ν τ X − ν τ . One such tensor correlation was looked for at LEP and 95% CL limits of Red z τ < 7.0×10 −17 e-cm from OPAL and Red z τ < 3.7×10 −17 e-cm from ALEPH were obtained from a sample of 650000 z's [8]. Recently it has been shown [9] that certain CP odd vector correlations in the reaction Theoretically it would be interesting to consider some extension of the SM that predicts real parts of WDFF and EDM at a level that is close to the precision range achievable at present or in near future experimental facilities.…”

Measurement of the τ electric dipole moment using longitudinal polarization ofe+e−Ananthanarayan1, Rindani2 1995Phys. Rev. D231100View full textAdd to dashboardCite

“…In particular, one may construct scalar, vector and tensor correlations [8] from the momenta q + and q − of the decay products of the τ + and τ − . One such tensor has been used to constrain the real part of the τ wdff from LEP data [9] where the Z contribution dominates the cross-section. Indeed, other tensor correlations have been found to be sensitive to the imaginary part of the wdff as well [10] and may be used at LEP to constrain it in the event of the absence of a significant non-zero measurement of such correlations.…”

“…The calculations include two-body decay modes of the τ in general and is applied specifically to the case of τ → π + ν τ and τ → ρ + ν τ due to the fact that these modes possess a good resolving power of the τ polarization, parametrized in terms of the constant α which takes the value 1 for the π channel (with branching fraction of about 11%) and 0.46 for the ρ channel [9] (with branching fraction of about 22%). It may be noted that with these final states the substantive fraction of the channels that are sensitive to such correlations are accounted for; three-body leptonic final states must also be included; they are characterized by a somewhat smaller α = −0.33 (with branching fraction of about 35%).…”