Weak dipole moment of τ\tau in e+e−e^+e^- collisions with longitudinally polarized electrons

It is pointed out that certain CP-odd momentum correlations in the production and subsequent decay of tau pairs in $e^+e^-$ collisions get enhanced when the $e^-$ is longitudinally polarized. Analytic expressions for these correlations are obtained for the single-pion decay mode of $\tau$ when $\tau^+\tau^-$ have a ``weak" dipole form factor (WDFF) coupling to $Z$ . For $e^+e^-$ collisions at the $Z$ peak, a sensitivity of about 1-5$\times 10^{-17}$\mbox{$e$ cm} for the $\tau$ WDFF can be reached using a {\em single} $\tau^+\tau^-$ decay channel, with $10^6\, Z$'s likely to be available at the SLC at Stanford with $e^-$ polarization of 62\%-75\%.Comment: 9 pages, Latex, PRL-TH-93/17 (Revised

CP Violation in Semileptonic τ\tau Decays with Unpolarized Beams

CP violating signals in semileptonic $\tau$ decays are studied. These can be observed in decays of unpolarized single $\tau$'s even if their rest frame cannot be reconstructed. No beam polarization is required. The importance of the two meson channel, in particular the $K\pi$ final state is emphasized.Comment: Latex, 17 pages, 2 figures. The complete paper, including figures, is also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints

CP violation at colliders

The prospects of experimental detection of $CP$ violation at $e^+e^-$ and $pp/p\overline{p}$ colliders are reviewed. After a general discussion on the quantities which can measure $CP$ violation and on the implications of the $CPT$ theorem, various possibilities of measuring $CP$ violation arising outside the standard model are taken up. $CP$ violation in leptonic processes, especially polarization effects in $e^+e^-\rightarrow l^+l^-$ are discussed next. $CP$ violation in $t\overline{t}$ and $W^+W^-$ production and decay is also described. (Based on talk presented at the WHEPP3, Madras, January 1994).Comment: 20 pages, latex, no figures (only revision is the comment that the article is based on a talk presented at WHEPP3, Madras, January 1994

Measurement of the τ\tau electric dipole moment using longitudinal polarization of e+e−e^+e^- beams

Certain CP-odd momentum correlations in the production and subsequent decay of $\tau$ pairs in $e^+ e^-$ collisions are enhanced significantly when the $e^+$ and $e^-$ beams are longitudinally polarized. These may be used to probe the real and imaginary parts of $d_\tau^\gamma$, the electric dipole moment of the $\tau$. Closed-form expressions for these ``vector correlations'' and the standard deviation of the operators defining them due to standard model interactions are presented for the two-body final states of $\tau$ decays. If 42\% average polarization of each beam is achieved, as proposed for the tau-charm factories, with equal integrated luminosities for each sign of polarization and a total yield of $2\cdot 10^7$ $\tau^+ \tau^-$ pairs, it is possible to attain sensitivities for $\vert\delta {\rm Re} d_{\tau}^{\gamma}\vert$ of $8\cdot 10^{-19}$, $1\cdot 10^{-19}$, $1\cdot 10^{-19}$ $e$ cm respectively and for $\vert\delta {\rm Im} d_{\tau}^{\gamma}\vert$ of $4\cdot 10^{-14}$, $6\cdot 10^{-15}$, $5\cdot 10^{-16}$ $e$ cm respectively at the three operating center-of-mass energies of 3.67, 4.25 and 10.58 GeV. These bounds emerge when the effects of a posible weak dipole form factor $d_\tau^Z$ are negligible as is the case when it is of the same order of magnitude as $d_\tau^\gamma$. Furthermore, in such a polarization experiment where different polarizations are possible, a model-independent disentangling of their individual effects is possible, and a technique to achieve this is described. A strong longitudinal polarization physics programme at the tau-charm factory appears warranted.Comment: 30 pages, latex, no figure

CP Violation Beyond the Standard Model and Tau Pair Production in e+e−e^+ e^- Collisions

We show that the CP-violating dipole form factors of the tau lepton can be of the order of $\alpha/\pi$ in units of the length scale set by the inverse $Z$ boson mass. We propose a few observables which are sensitive to these form factors at LEP2 and higher e^+e^- collision energies.Comment: 11 pages LaTeX + 2 figure

Tau Lepton Physics: Theory Overview

The pure leptonic or semileptonic character of tau decays makes them a good laboratory to test the structure of the weak currents and the universality of their couplings to the gauge bosons. The hadronic tau decay modes constitute an ideal tool for studying low-energy effects of the strong interactions in very clean conditions; a well-known example is the precise determination of the QCD coupling from tau-decay data. New physics phenomena, such as a non-zero tau-neutrino mass or violations of (flavour / CP) conservation laws can also be searched for with tau decays.Comment: 20 pages, latex, 5 Postscript figures, uses espcrc2.sty, Invited Talk at the Fourth International Workshop on Tau Lepton Physics (TAU96), Colorado, September 199

P and T Odd Asymmetries in Lepton Flavor Violating Tau Decays

We calculated the differential cross sections of the processes in which one of the pair created tau particles at an e^+ e^- collider decays into lepton flavor violating final states e.g. tau -> mu gamma, tau -> 3 mu, tau -> mu ee. Using the correlations between angular distributions of both sides of tau decays, we can obtain information on parity and CP violations of lepton flavor non-conserving interactions. The formulae derived here are useful in distinguishing different models, since each model of physics beyond the standard model predicts different angular correlations. We also calculate angular distributions of the major background process to tau -> l gamma search, namely tau -> l nu \bar{\nu} gamma, and discuss usefulness of the angular correlation for background suppression.Comment: 31 pages, 5 figure

Precision tau 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 tau physics, highlighting the most recent developments, and discuss the prospects for future improvements. The leptonic decays of the tau 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 -> l(+)l(-) decays. The hadronic tau 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-us have been obtained with tau data. The large mass of the tau 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 tau decays. Related subjects such as μdecays, the electron and muon anomalous magnetic moments, neutrino mixing and B-meson decays into tau leptons are briefly covered. Being one the fermions most strongly coupled to the scalar sector, the tau 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

The salient features of CP-violating interactions in the standard electroweak theory and in a few of its popular extensions are discussed. Moreover a brief overview is given on the status and prospects of searches for CP non-conservation effects in low and high energy experiments.Comment: 28 pages, Lectures given at the 37th Winter School on Particle Physics, Schladming, Austria, 199