0000000000224173
AUTHOR
Gabriel A. González-sprinberg
Tau anomalous magnetic moment form factor at Super B/Flavor factories
The proposed high-luminosity B/Flavor factories offer new opportunities for the improved determination of the fundamental physical parameters of standard heavy leptons. Compared to the electron or the muon case, the magnetic properties of the $\tau$ lepton are largely unexplored. We show that the electromagnetic properties of the $\tau$, and in particular its magnetic form factor, may be measured competitively in these facilities, using unpolarized or polarized electron beams. Various observables of the $\tau$'s produced on top of the $\Upsilon$ resonances, such as cross-section and normal polarization for unpolarized electrons or longitudinal and transverse asymmetries for polarized beams,…
Top quark tensor couplings
We compute the real and imaginary parts of the one-loop electroweak contributions to the left and right tensorial anomalous couplings of the $tbW$ vertex in the Standard Model (SM). For both tensorial couplings we find that the real part of the electroweak SM correction is close to 10$%$ of the leading contribution given by the QCD gluon exchange. We also find that the electroweak real and imaginary parts for the anomalous right coupling are almost of the same order of magnitude. The one loop SM prediction for the real part of the left coupling is close to the 3$\sigma$ discovery limit derived from $b\rightarrow s \gamma$. Besides, taking into account that the predictions of new physics int…
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 ind…
The top quark right coupling in the tbW-vertex
The most general parametrization of the $tbW$ vertex includes a right coupling $V_R$ that is zero at tree level in the standard model. This quantity may be measured at the Large Hadron Collider where the physics of the top decay is currently investigated. This coupling is present in new physics models at tree level and/or through radiative corrections, so its measurement can be sensitive to non standard physics. In this paper we compute the leading electroweak and QCD contributions to the top $V_R$ coupling in the standard model. This value is the starting point in order to separate the standard model effects and, then, search for new physics. We also propose observables that can be address…
Top quark anomalous tensor couplings in the two-Higgs-doublet models
We compute the one loop right and left anomalous tensor couplings (g(R) and g(L), respectively) for the top quark, in the aligned two-Higgs-doublet model. They are the magnetic-like couplings in the most general parameterization of the tbW vertex. We find that the aligned two-Higgs doublet model, that includes as particular cases some of the most studied extensions of the Higgs sector, introduces new electroweak contribution's and provides theoretical predictions that are very sensitive to both new scalar masses and the neutral scalar mixing angle. For a largo area in the parameters space we obtain significant deviations in both the real and the imaginary parts of the couplings gR and gL, c…
Anomalous top magnetic couplings
The real and imaginary parts of the one-loop electroweak contributions to the left and right tensorial anomalous couplings of the tbW vertex in the Standard Model (SM) are computed.
IMPROVED BOUNDS ON THE TAU MAGNETIC MOMENTS
New limits on the tau magnetic couplings to the photon, the Z and the W bosons are obtained from the most general effective Lagrangian. Model independent bounds are set using data for tau pair production and W decay into tau leptons at LEP1, LEP2, SLD and hadron colliders. For the anomalous magnetic moment the bounds are, for the first time, of the order of magnitude of the standard model prediction.
EDM observables for τ production with polarized beams
The Tau-lepton electric dipole moment (EDM) can be measured at Super B/Flavor factories operating with polarized electron beams at energies near and on top of the ¤ resonances. In particular, new CP-odd observables, independent from others already considered, will allow to put stringent bounds on the ? EDM.
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.
CP violation and electric-dipole moment at low energy tau production with polarized electrons
10 pages, 2 figures.-- ISI Article Identifier: 000243912400014.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0610135
The tau weak-magnetic dipole moment
We calculate the prediction for the anomalous weak-magnetic form factor of the tau lepton at $q^2=M_Z^2$ within the Standard Model. With all particles on-shell, this is a electroweak gauge invariant quantity. Its value is $a_\tau^w (M_Z^2)= - \;(2.10 + 0.61\, i) \times 10^{-6}$. We show that the transverse and normal components of the single-tau polarization of tau pairs produced at $e^+e^-$ 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.
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 $\tau$ magnetic moment $a_\tau$ 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 …
Model independent bounds on the tau lepton electromagnetic and weak magnetic moments
Using LEP1, SLD and LEP2 data, for tau lepton production, and data from CDF, D0 and LEP2, for W decays into tau leptons, we set model independent limits on non-standard electromagnetic and weak magnetic moments of the tau lepton. The most general effective Lagrangian giving rise to tau moments is used without further assumptions. Precise bounds ($2\sigma$) on the non-standard model contributions to tau electromagnetic ($-0.007<a_\gamma< 0.005$), tau Z-magnetic ($-0.0024 <a_Z< 0.0025$) and tau W-magnetic ($-0.003 < \kappa^W < 0.004$) dipole moments are set from the analysis.
Top quark decay in the Aligned two-Higgs-doublet Model
AbstractWe compute the one loop right and left anomalous tensor couplings (gR and gL, respectively) for the top quark, in the aligned two-Higgs-doublet model. They are the magnetic-like couplings in the most general parameterization of the tbW vertex. We find that the aligned two-Higgs doublet model, that includes as particular cases some of the most studied extensions of the Higgs sector, as Type I and II 2HDM, introduces new electroweak contributions and provides theoretical predictions that are very sensitive to both new scalar masses and the neutral scalar mixing angle. The model can account for new CP violation effects via the introduction of complex alignment parameters that have impo…
Tau weak dipole moments from azumthal asymmetries
We show that transverse and normal single-$tau$ polarization of $tau$ pairs produced at $e^+$ $e^-$ unpolarized collisions, at the $Z$ peak, are sensitive to weak (magnetic and electric) dipole moments of the $tau$. We also show how these components of the $\tau$ polarization are accessible by measuring appropriate azimuthal asymmetries in the angular distribution of its decay products. Sensitivities of the order of $10^{-18}$ $e\cdot cm$, for the weak-electric dipole moment, and $10^{-4}$ ($10^{-3}$), for the real (imaginary) part of the weak-magnetic dipole moment of $\tau$, may be achieved. Compatible bounds are also presented from spin-spin correlated asymmetries.
τ EDM at low energies
Low energy tau pair production, at B factories and on top of the $\Upsilon$ resonances, allows for a detailed investigation on the CP violation at the electromagnetic tau pair production vertex. High statistic available at low energies offers the opportunity for an independent analysis of CP-violation in the $\tau$ lepton physics. We show that stringent and independent bounds on the $\tau$ electric dipole moment, competitive with the high energy measurements, can be established in low energies experiments.
Bounds on the Tau Magnetic Moments: Standard Model and Beyond
We obtain new bounds for the magnetic dipole moments of the tau lepton. These limits on the magnetic couplings of the tau to the electroweak gauge bosons (gamma, W, Z) are set in a model independent way using the most general effective Lagrangian with the SU(2)_L x U(1)_Y symmetry. Comparison with data from the most precise experiments at high energies shows that the present limits are more stringent than the previous published ones. For the anomalous magnetic moment the bounds are, for the first time, within one order of magnitude of the standard model prediction.