τ lepton decays

We discuss recent results on τ lepton physics obtained at the BABAR,Belle and KEDR detectors.They include tests of lepton universality using new measurements of τ lepton mass and some branching fractious.Also described are selected results on τ lepton hadronic decays coming from BABAR and Belle.     

Rare decays of the tau lepton at Belle

We report recent results of searches for lepton flavor violation and second class current in decays of τ leptons using the data sample collected in the Belle experiment at the KEKB electron-positron asymmetric-energy collider.     

The new heavy lepton τ

Experimental evidence for the production of the heavy lepton τ ine ⁺ e ^? annihilation and the determination of its properties are reviewed. All data are in good agreement with the predictions of the heavy lepton hypothesis.     

Analytic Approximation for Process e++e－→τ++τ－ Cross Section Near Threshold

In the structure function approach,we calculate the threshold behaviours for e⁺+e^－→τ⁺+τ^－,which including QED radiative corrections from initial correction,vacuum polarization effect,Coulomb effect and final state correction.This theoretical prediction for threshold behaviours of τ-pair production is useful for BES new measurement of lepton τ mass.     

Precise Measurement of τ Mass

Pairs of τ lepton produced near the threshould have been studied in eμ,ee,eπ,μμ,μπ,ππ final states with the data taken by BES detector at BEPC collider in 1992.The obtained τ mass is MeV by fitting data with likelihood method.     

The Implications of the New Measurement of τ Lepton Mass

We discuss the physical implications for the new measurement of τ lepton mass.The Value of τ lifetime is predictcd.     

(Quasi)elastic large-angle electron-muon scattering in the two-loop approximation: Contributions of the eikonal type

A part of the eikonal-type contributions to the eμ large-angle high-energy scattering cross section is considered in a quasielastic experimental setup. In addition to virtual corrections, we examine inelastic processes with emission of one and two soft real photons and soft lepton and pion pairs. Virtual photon contributions are given within a logarithmic accuracy. Box-type Feynman amplitudes with leptonic and a hadronic vacuum polarization insertion and double-box ones are considered explicitly. Wherever appropriate, the analytic expressions obtained are compared with those predicted by the structure function approach.     

Hadronic quantum numbers beyond charm as a possible source of v induced trimuons

Characteristics of trimuons emerging from cascade decay of two new hadronic quantum numbers are compared with experiments. The possibility that the lower (spinless) member decays preferentially into Perl's sequential heavy lepton τ via τ + ν_τ is incorporated.     

Decays of the heavy lepton τ and chiral dynamics

Predictions for the semihadronic decays of the heavy lepton τ intov _τ+nπ are derived from chiral dynamics using the method of phenomenological Lagrangians. For low hadron energy the only free parameter is the π decay constantf _π. For the total decay rates the ? has been included as final state interaction. These rates are compared with existing data.     

Infrared reflectivity and coupled modes in Gd-doped EuO

The reflectivity of EuO single crystals, doped with various amounts of Gd, has been measured between 250μ and 12 eV photon energy. A Kramers-Kronig analysis of the data reveals LO and TO phonon modes, plasmons and LO phonon-plasmon coupled modes.     

Measurement of the τ lepton lifetime

The mean lifetime of the τ lepton is measured in a sample of 25700 τ pairs collected in 1992 with the ALEPH detector at LEP. A new analysis of the 1-1 topology events is introduced. In this analysis, the dependence of the impact parameter sum distribution on the daughter track momenta is taken into account, yielding improved precision compared to other impact parameter sum methods. Three other analyses of the one- and three-prong τ decays are updated with increased statistics. The measured lifetime is 293.5±3.1± 1.7 fs. Including previous (1989–1991) ALEPH measurements, the combined τ lifetime is 293.7±2.7±1.6fs.     

Radiative corrections to semileptonic decays of charged hyperons

We have studied the radiative corrections to the lepton energy spectrum in semileptonic hyperon decays. The calculation is performed relativistically for the baryons as well as for the leptons, under the assumption of the effective current-current interaction of the V-?A type for the baryonic part. We obtain the explicit formula of radiative corrections to the lepton energy spectrum which we can exactly evaluate in case of charged hyperon decays. Numerical values of the radiative corrections to the decays rate and the shape of the lepton energy spectrum are also given for some decay modes. It is shown that the spectral shape is little affected by the radiative corrections.     

Constraints on the masses and couplings of heavy Majorana right-handed neutrinos

The masses and couplings of heavy unstable right-handed Majorana neutrinos can be constrained using existing and expected future results from both accelerator and astrophysics experiments. In particular we examine limits on rare decay modes of particles containing s, c, and b quarks as well as the τ lepton and interpret these in terms of a hypothetical massive neutrino. In addition, cosmological limits result from a consideration of the nucleosynthesis epoch in the early universe.     

高能物理的实验现状

本文简要介绍国内外高能物理发展的最新状况,概述了国外对顶夸克存在的证据、电弱相互作用的精密检验及重味物理与轻子物理的进展．另外,还介绍了在北京谱仪上,有关τ质量测量、Ｊ／ψ衰变性质、ψ衰变性质及Ｄｓ衰变性质方面的最新结果． The recent experiment status of high energy physics in the world are presented briefly.The evidence for the TOP quark,precision test of EW interaction, heavy flavor physics and lepton physics are summarized in the first part. The second part introduces the new results on τ mass measurement,ψ decay,Ds decay and J/ψ decay performance from BES.     

Spontaneously broken e-μ-τ symmetry and rare τ decays

Suppose that all differences between the leptons e, μ and τ arise from spontaneous symmetry breaking. Implementation of this idea in the standard gauge model leads to conservation of multiplicative rather than additive lepton number. The consequences of this are analysed.     

“Anomalous” eta production in tau decay

The decay modes of the τ lepton involving η particles in the final state are analyzed. Some of these channels are related to the non-abelian chiral anomaly of QCD. It is found that the τ⁻→ν_τπ⁻ηπ⁰ mode dominates the inclusive production of η mesons in τ decay.     

Processes with heavy ion collisions

Some Coulomb effects in heavy ion collisions are considered. Among them the process of muon and lepton pair creation, Coulomb and unitary corrections, statistics of multiple pair production. Effects of multiple photon exchange in process of lepton pair production by linearly polarized photon on nuclei are considered. This process is used for measuring the polarization of initial photon. Relativistic muon energy loss due to the light lepton pair production in the Coulomb field are calculated. Also we consider the effects of multiple photon exchange in elastic lepton scattering on unscreened atomic field and discuss the possible experimental testing.     

Azimuthal distributions in radiative decay of a polarized τ lepton

We investigate various distributions over emitted photon angles, especially over the azimuthal angle, in the one-meson radiative decay of the polarized τ lepton, τ^– → π^–γν_τ. In connection with this, the photon phase space is discussed in more detail because it is nontrivial in the case of a polarized τ lepton. The decay matrix element contains both the inner bremsstrahlung and the resonance (structural) contributions. The azimuthal dependence of some observables are calculated. They are the asymmetry of the differential decay width caused by the τ-lepton polarization, the Stokes parameters of the emitted photon itself, and the correlation parameters describing the influence of τ-lepton polarization on the photon Stokes parameters. A numerical estimation is done in the τ-lepton rest frame for an arbitrary direction of the τ-lepton polarization 3-vector. The vector and axial-vector form factors describing the structure-dependent part of the decay amplitude are determined using the chiral effective theory with resonances (RχT). It is found that the features of the azimuthal distributions allows separating various terms in the spin-dependent contribution. The so-called up–down and right–left asymmetries are also calculated.     

Uncertainties in τ polarization measurement at SLC/LEP and QED/electroweak radiative corrections

We discuss the τ polarization measurement at SLC/LEP energies as a data point in the precision tests of the Glashow-Salam-Weinberg model. Theoretical and experimental uncertainties of this measurement are examined and it is concluded that apart from left-right asymmetry measurement, and for typical values of the parameters of the Standard Model, the τ polarization offers the best probe of the couplings of leptons to the Z⁰. In particular, the dependence of the τ polarization on the top and Higgs masses is discussed. The interplay of QED initial state bremsstrahlung and other classes of radiative corrections is also discussed.