Search for anomalous weak dipole moments of the $\tau$ lepton

The anomalous weak dipole moments of the lepton are measured in a data sample collected by ALEPH from 1990 to 1995 corresponding to an integrated luminosity of 155 pb^-1. Tau leptons produced in the reaction at energies close to the mass are studied using their semileptonic decays to , , or . The real and imaginary components of both the anomalous weak magnetic dipole moment and the CP-violating anomalous weak electric dipole moment, , , and , are measured simultaneously by means of a likelihood fit built from the full differential cross section. No evidence of new physics is found. The following bounds are obtained (95% CL): , , , and .Received: 25 September 2002, Published online: 29 August 2003     

Supersymmetry and the anomalous anomalous magnetic moment of the muon

The recently reported measurement of the muon's anomalous magnetic moment differs from the standard model prediction by 2.6 sigma. We examine the implications of this discrepancy for supersymmetry. Deviations of the reported magnitude are generic in supersymmetric theories. Based on the new result, we derive model-independent upper bounds on the masses of observable supersymmetric particles. We also examine several model frameworks. The sign of the reported deviation is as predicted in many simple models, but disfavors anomaly-mediated supersymmetry breaking.     

Anomalous $\eta/\eta^\prime$ decays: the triangle and box anomalies

We examine the decay modes within the context of the hidden local symmetry (HLS) model. Using numerical information derived in previous fits to the and Ve ⁺ e ^- decay modes in isolation and the lineshape determined in a previous fit to the pion form factor, we show that all aspects of these decays can be predicted with fair accuracy. Freeing some parameters does not improve the picture. This is interpreted as strong evidence in favor of the box anomaly in the decays, which occurs at precisely the level expected. We also construct the set of equations defining the amplitudes for and at the chiral limit, as predicted from the anomalous HLS Lagrangian appropriately broken. This provides a set of four equations depending on only one parameter, instead of three for the traditional set. This is also shown to match the (two-angle, two-decay-constant) - mixing scheme recently proposed and is also fairly well fulfilled by the data. The information returned from the fits also matches expectations from previously published fits to the decay modes in isolation.Received: 29 June 2003, Revised: 17 September 2003, Published online: 4 November 2003     

Study of \tau decays involving kaons, spectral functions and determination of the strange quark mass

All ALEPH measurements of branching ratios of decays involving kaons are summarized including a combination of results obtained with and detection. The decay dynamics are studied, leading to the determination of contributions from vector and , and axial-vector and resonances. Agreement with isospin symmetry is observed among the different final states. Under the hypothesis of the conserved vector current, the spectral function for the mode is compared with the corresponding cross section for low energy annihilation, yielding an axial-vector fraction of for this mode. The branching ratio for decay into all strange final states is determined to be . The measured mass spectra of the strange decay modes are exploited to derive the spectral function. A combination of strange and nonstrange spectral functions is used to determine the strange quark mass and nonperturbative contributions to the strange hadronic width. A method is developed to avoid the bad convergence of the spin zero hadronic component, with the result MeV/. The evolution down to 1 GeV gives . Received: 24 February 1999 / Published online: 14 October 1999     

Polarisation in sfermion decays: determining $\tan\beta$ and trilinear couplings

The basic parameters of supersymmetric theories can be determined at future e ⁺ e ^- linear colliders with high precision. We investigate in this report how polarisation measurements in and or decays to leptons and t quarks plus neutralinos or charginos can be used to measure (in particular for large values) and to determine the trilinear couplings , A _t and A _b in sfermion pair production.Received: 17 April 2003, Revised: 3 July 2003, Published online: 29 August 2003     

New definition for the hadronic contribution to the muon anomalous magnetic moment

A new definition is proposed for the hadronic contribution to the muon anomalous magnetic moment that is based on the inclusion of the effects of vacuum polarization by leptons into the cross section for one-photon annihilation of a lepton pair into hadrons. The formula for the hadronic contribution includes the convolution of the measured cross section for annihilation into hadrons with a certain standard function. This remark concerns radiative correction to this function. A particular form has been proposed for this correction. It has been shown that the use of the new function makes it possible to reduce the uncertainty in such contributions due to radiative correctioins to δa _h/a _h ～ 10^?4.     

Low energy supergravity and the anomalous magnetic moment of the muon

The anomalous magnetic moment of the muon (g ? 2)_μ imposes constraints on the masses and mixings of spin-zero leptons, gauge fermions, and Higgs fermions in minimal models of low energy supergravity. We demonstrate that there exist only limited values of the parameters in these models that are ruled out by existing limits on (g ? 2)_μ.     

Estimating scalar-leptoquark masses from the muon anomalous magnetic moment within the four-color symmetry model

The contributions to the muon anomalous magnetic moment from the doublets of scalar leptoquarks having a four-color origin are studied. It is shown that experimental data on the muon anomalous magnetic moment are compatible with the existence of relatively light scalar leptoquarks (of mass about 1 TeV or below).     

Measurement of the magnetic moment of a negative muon in zinc and cadmium

The magnetic moment (g factor) of a negative muon on the 1s atomic levels of zinc and cadmium was measured with an accuracy higher by a factor of 7 than the accuracy achieved in other measurements. The experimental value of the g factor differs substantially from the theoretical results. Possible causes of this discrepancy are discussed.     

Searches for the appearance of \nu_\tau using neutrino beams from muon storage rings

We study the possibilities offered by muon storage rings for appearance experiments in order to determine masses and mixing angles for the and oscillations. The dependence of tau event rates on baseline, forward peaking of decay neutrinos with increasing energies, and average fluxes intercepted by detectors of various sizes is discussed. It is found that the baseline length does not significantly affect the rates for oscillations of such magnitudes as are suggested by the current atmospheric neutrino data. Subsequently, the effects of cuts on hadronic and wrong sign leptonic modes are computed and used to plot 90% CL contours for the parameter regions that can be explored in such experiments. The results show that even for modest muon beam energies, convincing coverage and verification of the Super Kamiokande parameters is possible. In addition, a very significant enlargement of present day bounds on the mixing parameters for neutrino oscillations of all types is guaranteed by these types of searches. Received: 4 April 2000 / Revised version: 22 July 2000 / Published online: 8 December 2000     

Radiative return at $\Phi$ - and B-factories: FSR for muon pair production at next-to-leading order

Muon pair production through the radiative return is of importance for a measurement of the hadronic production cross section in two ways: it provides an independent calibration and it may give rise to an important background for the measurement of the pion form factor. With this motivation the Monte Carlo event generator PHOKHARA is extended to include next-to-leading order radiative corrections to the reaction . Furthermore, virtual ISR corrections to FSR from pions are introduced, which extends the applicability of the generator into a new kinematical regime. Finally, the effect of photon vacuum polarization is introduced into this new version of the generator.Received: 8 April 2004, Revised: 3 December 2004, Published online: 25 January 2005Work supported in part by BMBF under grant number 05HT9VKB0, EC 5th Framework Programme under contract HPRN-CT-2002-00311 (EURIDICE network), TARI project HPRI-CT-1999-00088, Polish State Committee for Scientific Research (KBN) under contract 2 P03B 017 24, BFM2002-00568, Generalitat Valenciana under grant GRUPOS03/013, and MCyT under grant FPA-2001-3031.     

Neutrino oscillation and magnetic moment from \nu - e^{-} elastic scattering

We discuss how the measurement of the elastic cross section at reactor energies can be used to extract new information on the neutrino oscillation parameters. We also consider the magnetic moment contribution and show how both effects tend to cancel each other when the total cross section is measured. To achieve the separation of each of the effects, experiments capable of measuring angular and energy distributions with respect to the outgoing electron become necessary. The sensitivity of these kind of experiments to magnetic moments, masses and mixings is discussed. We also discuss the possibility of measuring the magnetic moment of neutrinos via oscillation. Received: 12 September 1997 / Revised version: 22 December 1997 / Published online: 10 March 1998