Electromagnetic properties of the tau lepton from Z0 decay

doi:10.1016/0370-2693(91)90276-V

Physics Letters B

Volume 255, Issue 4, 21 February 1991, Pages 611-612

https://doi.org/10.1016/0370-2693(91)90276-V Get rights and content

Abstract

We explore the potentialities of the radiative decay Z→τ⁺τ⁻γ at Z factories to constrain and eventually measure the magnetic moment and the electric dipole moment of the τ lepton. In particular, we use existing LEP data to bound both static quantities in a kinematic domain not accesible in previous experiments.

References (3)

F. del Aguila et al.
preprint WM-TH-90-109
(1990)

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Cited by (71)

Model-independent study on the anomalous ττ¯γ couplings at the ILC
2021, Nuclear Physics B
Citation Excerpt :
If there considers a coupling of leptons in new physics beyond the SM, electric dipole moment may induce the detectable size of CP-violation [22–29]. As a result, the magnetic and electric dipole moments of the tau lepton allow stringent testing for new physics beyond SM and have been studied in detail by Refs. [31–49]. The advantage of linear colliders with respect to hadron colliders is in the general cleanliness of the events where two elementary particles, electron and positron beams, collide at high energy, and the high resolutions of the detector are made possible by the relatively low absolute rate of background events.
The potential of the process $γ γ \to τ \bar{τ} γ$ is examined in a model-independent way using the effective Lagrangian approach for the International Linear Collider, a proposed electron-positron machine which is designed with standard configurations of 0.25 TeV/2000 fb⁻¹, 0.35 TeV/200 fb⁻¹ and 0.5 TeV/4000 fb⁻¹. The limits obtained for the tau lepton's anomalous magnetic dipole moment ${\tilde{a}}_{τ}$ and the tau lepton's anomalous electric dipole moment ${\tilde{d}}_{τ}$ defining the anomalous $τ \bar{τ} γ$ couplings at 95% confidence level and systematic uncertainties of $δ_{s y s} = 0, 5, 10 %$ are compared with the experimental results. The best limits obtained with $δ_{s y s} = 0 %$ on the anomalous couplings are $- 0.00082 < {\tilde{a}}_{τ} < 0.00050$ and $| \tilde{d_{τ}} | < 3.59 \times 10^{- 18}$ $e cm$ , respectively. Also, the limits on the anomalous couplings do not improve proportionately to the luminosity due to the systematic error considered here. The reason of this situation is the systematic error which is much bigger than the statistical error. If the systematic error is improved, we expect better limits on the couplings. However, the best limits on the anomalous couplings for the process $γ γ \to τ \bar{τ} γ$ with $\sqrt{s} = 500$ GeV, $L_{i n t} = 4000$ fb⁻¹ and $δ_{s y s} = 0 %$ can be improved up to 4 times for ${\tilde{a}}_{τ}$ and 9 times for ${\tilde{d}}_{τ}$ according to case with $δ_{s y s} = 10 %$ . Our results show that γγ collisions at the ILC give results up to one order of magnitude for ${\tilde{a}}_{τ}$ and two orders of magnitude for ${\tilde{d}}_{τ}$ better than the current experimental limits.
A call for new physics: The muon anomalous magnetic moment and lepton flavor violation
2018, Physics Reports
We review how the muon anomalous magnetic moment ( $g - 2$ ) and the quest for lepton flavor violation are intimately correlated. Indeed the decay $μ \to e γ$ is induced by the same amplitude for different choices of in- and outgoing leptons. In this work, we try to address some intriguing questions such as: Which hierarchy in the charged lepton sector one should have in order to reconcile possible signals coming simultaneously from $g - 2$ and lepton flavor violation? What can we learn if the $g - 2$ anomaly is confirmed by the upcoming flagship experiments at FERMILAB and J-PARC, and no signal is seen in the decay $μ \to e γ$ in the foreseeable future? On the other hand, if the $μ \to e γ$ decay is seen in the upcoming years, do we need to necessarily observe a signal also in $g - 2$ ?. In this attempt, we generally study the correlation between these observables in a detailed analysis of simplified models. We derive master integrals and fully analytical and exact expressions for both phenomena, and address other flavor violating signals. We investigate under which conditions the observations can be made compatible and discuss their implications. Lastly, we discuss in this context several extensions of the SM, such as the Minimal Supersymmetric Standard Model, Left–Right symmetric model, $B$ – $L$ model, scotogenic model, two Higgs doublet model, Zee–Babu model, 331 model, and $L_{μ} - L_{τ}$ , dark photon, seesaw models type I, II and III, and also address the interplay with $μ \to e e e$ decay and $μ$ – $e$ conversion.
Limits on the electromagnetic and weak dipole moments of the tau-lepton in a 331 model
2014, Nuclear Physics B - Proceedings Supplements
Using as an input the data obtained by the L3 and OPAL Collaborations for the reaction $e^{+} e^{-} \to τ^{+} τ^{-} γ$ at the $Z_{1}$ -pole, we obtained bounds on the electromagnetic and weak dipole moments of the tau-lepton in the context of a 331 model. Our bounds on the electromagnetic moments are consistent with the bounds obtained by the L3 and OPAL Collaborations for the reaction $e^{+} e^{-} \to τ^{+} τ^{-} γ$ . We also obtained bounds on the tau weak dipole moments which are consistent with the bounds obtained recently by the DELPHI, ALEPH and BELLE Collaborations from the reaction $e^{+} e^{-} \to τ^{+} τ^{-}$ . Our work complements other studies on the electromagnetic and weak dipole moments of the tau-lepton.
Towards a determination of the tau lepton dipole moments
2014, Nuclear Physics B - Proceedings Supplements
The τ anomalous magnetic moment $a_{τ}$ and electric dipole moment $d_{τ}$ have not yet been observed. The present bounds on their values are of order $10^{- 2}$ and $10^{- 17} e cm$ , respectively. We propose to measure $a_{τ}$ with a precision of $O (10^{- 3})$ or better and improve the existing limits on $d_{τ}$ using precise $τ^{-} \to l^{-} ν_{τ} {\bar{ν}}_{l} γ$ ( $l = e$ or μ) data from high-luminosity B factories. A detailed feasibility study of this method is underway.
Precision tau physics
2014, Progress in Particle and Nuclear Physics
Precise measurements of the lepton properties provide stringent tests of the Standard Model and accurate determinations of its parameters. We overview the present status of $τ$ physics, highlighting the most recent developments, and discuss the prospects for future improvements. The leptonic decays of the $τ$ lepton probe the structure of the weak currents and the universality of their couplings to the $W$ boson. The universality of the leptonic $Z$ couplings has also been tested through $Z \to ℓ^{+} ℓ^{-}$ decays. The hadronic $τ$ decay modes constitute an ideal tool for studying low-energy effects of the strong interaction in very clean conditions. Accurate determinations of the QCD coupling and the Cabibbo mixing $V_{u s}$ have been obtained with $τ$ data. The large mass of the $τ$ opens the possibility to study many kinematically-allowed exclusive decay modes and extract relevant dynamical information. Violations of flavour and CP conservation laws can also be searched for with $τ$ decays. Related subjects such as $μ$ decays, the electron and muon anomalous magnetic moments, neutrino mixing and $B$ -meson decays into $τ$ leptons are briefly covered. Being one the fermions most strongly coupled to the scalar sector, the $τ$ lepton is playing now a very important role at the LHC as a tool to test the Higgs properties and search for new physics at higher scales.
CP violation and electric-dipole-moment at low energy τ production with polarized electrons
2007, Nuclear Physics B
The new proposals for high luminosity B/Flavor factories, near and on top of the ϒ resonances, allow for a detailed investigation of CP-violation in the τ-pair production. In particular, bounds on the tau electric dipole moment can be obtained of genuine CP-odd observables related to the τ-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 previous bounds, can be obtained.

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^☆: Work partially supported by the research project CICYT-AEN90-0028.

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Electromagnetic properties of the tau lepton from Z0 decay☆

Abstract

preprint WM-TH-90-109

Electromagnetic properties of the tau lepton from Z⁰ decay☆