10 research outputs found
CP violation and electric-dipole-moment at low energy production with polarized electrons
The new proposals for high luminosity B/Flavor factories, near and on top of
the resonances, allow for a detailed investigation of CP-violation
in the -pair production. In particular, bounds on the tau electric dipole
moment can be obtained from genuine CP-odd observables related to the
-pair production. We perform an independent analysis from low energy (10
GeV) data by means of linear spin observables. We show that, for a
longitudinally polarized electron beam, a CP-odd asymmetry, associated to the
normal polarization term, can be measured at these low energy facilities both
at resonant and non resonant energies. In this way, stringent and independent
bounds to the tau electric dipole moment, which are orders of magnitude below
other high or low energy bounds, can be obtained.Comment: 12 pages, 2 figure
CP violation and electric-dipole-moment at low energy tau-pair production
CP violation at low energy is investigated at the tau electromagnetic vertex.
High statistics at B factories, and on top of the Upsilon resonances, allows a
detailed investigation of CP-odd observables related to the tau-pair
production. The contribution of the tau electric dipole moment is considered in
detail. We perform an analysis independent from the high energy data by means
of correlation and linear spin observables at low energy. We show that
different CP-odd asymmetries, associated to the normal-transverse and
normal-longitudinal correlation terms can be measured at low energy
accelerators, both at resonant and non resonant energies. These observables
allow to put stringent and independent bounds to the tau electric dipole moment
that are competitive with other high or low energy results.Comment: 18 pages, 2 figures, references added, minor changes in section 3 and
5, to be published in Nucl.Phys.
Tau spin correlations and the anomalous magnetic moment
We show that the precise determination of the Tau magnetic properties is
possible in the next generation accelerators, specially at B/Flavour factories.
We define spin correlation observables suitable to extract the real part of the
magnetic form factor that, for the first time, will allow to test the standard
model-QED predictions. In particular, the predicted QED-dependence with both
the momentum transfer and the lepton mass can be precisely measured. Until now,
the most stringent bounds on the magnetic moment come from LEP
data with strong assumptions on the physics involved on the observed process.
In this paper, we find three different combinations of spin correlations of the
outgoing Taus that disentangle the magnetic moment form factor of the Tau
lepton in the electromagnetic vertex. These combinations of asymmetries also
get rid off the contributions coming from Z-mediating amplitudes to the defined
correlations. Using unpolarized electron beams and an integrated luminosity of
, the sensitivity to the magnetic moment form
factor is of the order . This sensitivity is two orders of magnitude
better than the present existing high- or low-energy bounds on the magnetic
moment and would allow its actual measurement with the precision of a few per
cent.Comment: 14 pages, 1 figur
The Weak-Magnetic Moment of Heavy Quarks
With initial and final particles on-shell, the anomalous weak-magnetic dipole
moments of b and c quarks are electroweak gauge invariant quantities of the
effective couplings Zb\bar{b} and Zc\bar{c}, respectively, and good candidates
to test the Standard Model and/or new physics. Here we present a complete
computation of these quantities within the Standard Model. We show that
decoupling properties with respect to heavy particles do take place in the weak
magnetic moment. The obtained values, a_b(M_Z^2)=(2.98-1.56i)x10^(-4) and
a_c(M_Z^2)=(-2.80+1.09i)x10^(-5) are dominated by one-gluon exchange diagrams.
The electroweak corrections are less than 1% of the total magnitude.Comment: 12 pages, 1 Postscript figure, LaTeX. 1 reference corrected.
Published in Phys. Lett.
The tau weak-magnetic dipole moment
We calculate the prediction for the anomalous weak-magnetic form factor of
the tau lepton at within the Standard Model. With all particles
on-shell, this is a electroweak gauge invariant quantity. Its value is
. We show that the
transverse and normal components of the single-tau polarization of tau pairs
produced at unpolarized collisions are sensitive to the real and
absorptive parts of the anomalous weak-magnetic dipole moment of the tau. The
sensitivity one can achieve at LEP in the measurement of this dipole moment is
discussed.Comment: 16 pages, Latex, 2 figure
The Landau Pole and decays in the 331 bilepton model
We calculate the decay widths and branching ratios of the extra neutral boson
predicted by the 331 bilepton model in the framework of two
different particle contents. These calculations are performed taken into
account oblique radiative corrections, and Flavor Changing Neutral Currents
(FCNC) under the ansatz of Matsuda as a texture for the quark mass matrices.
Contributions of the order of are obtained in the branching
ratios, and partial widths about one order of magnitude bigger in relation with
other non- and bilepton models are also obtained. A Landau-like pole arise at
3.5 TeV considering the full particle content of the minimal model (MM), where
the exotic sector is considered as a degenerated spectrum at 3 TeV scale. The
Landau pole problem can be avoid at the TeV scales if a new leptonic content
running below the threshold at TeV is implemented as suggested by other
authors.Comment: 20 pages, 5 figures, LaTeX2
FCNC Top Quark Decays in Extra Dimensions
The flavor changing neutral top quark decay t -> c X is computed, where X is
a neutral standard model particle, in a extended model with a single extra
dimension. The cases for the photon, X= \gammaR_\xi gauge. We find that
the branching ratios can be enhanced by the dynamics originated in the extra
dimension. In the limit where 1/R >> ->, we have found Br(t -> c \gamma) \simeq
10^{-10} for 1/R = 0.5 TeV. For the decay t -> c H, we have found Br(t -> cH)
\simeq 10^{-10} for a low Higgs mass value. The branching ratios go to zero
when 1/R -> \infty.Comment: Accepted to be published in the Europ. Phys. Jour. C; 16 pages, 2
figure
Normal and transverse single tau-polarization at the z-peak
We study normal (to the collision plane) and transverse (within the collision plane) single-τ polarization in τ pairs produced in e+e− unpolarized collisions at the Z-resonance. The transverse polarization component is sensitive to the anomalous weak-magnetic moment, whereas the normal polarization component is sensitive to a CP-violating weak-electric dipole moment. We show how these components of the single τ polarization are accessible from the angular distribution of its decay products. We define a CP violating asymmetry of the τ decay products which, with 107Z′s produced, provides a sensitivity of 2.3 × 10−18e·cm for the weak-electric dipole moment