The muon spectra from decays ofW- andZ-bosons produced ine + e −-collisions

The muon spectra from the decays ofW-andZ-bosons, produced ine ⁺ e ^?→W ⁺ W ^?,e ⁺ e ^?→Zγ,e ⁺ e ^?→ZZ ande ⁺ e ^?→ZH reactions have been obtained (H is the Higgs boson). It has been shown (in terms of Glashow-Weinberg-Salam theory) that the main source of muons are thee ⁺ e ^?→Zγ ande ⁺ e ^?→W ⁺ W ^? processes (over theW-boson production threshold). The contribution of thee ⁺ e ^?→ZZ ande ⁺ e ^?→ZH reactions to the inclusive muon spectra is small. It has been also shown, that it is possible to distinguish contributions of thee ⁺ e ^?→Zγ ande ⁺ e ^?→W ⁺ W ^? reactions if the decay muons move at a small angle to the initial electron momentum.     

Possible structures of the neutral current within a gauge theory framework

We examine a class of gauge theories based on U(1)×SU(2)×G allowing for an arbitrary number of gauge bosons, while retaining the lowq ² four fermion interaction of the standard model. Measurable consequences fore ⁺ e ^?→μ ⁺ μ ^? ande ⁺ e ^?→e ⁺ e ^? at presently available as well as LEP energies are presented. Implications of the recently determined QED cut-offΛ _? ? 100 GeV on gauge boson properties and the anomalous magnetic moment of the muon are pointed out.     

Study of some rare decays of the K+ meson

In a search for very rare decays of the K⁺ meson we observed the K⁺→μ⁺νe⁺e^? and K⁺→e⁺ν e⁺e^? modes with branching ratios of (10±3) ×10^?7 and (2⁺²_?2)×10^?7 respectively. We also put new limits on a decay allowed by the alternate scheme of lepton conservation K⁺→π^?μ⁺e⁺, on a decay with double charged weak current K⁺→π^? e⁺e⁺ and on other forbidden decays K⁺→μ^?νe⁺e⁺ and K⁺→π⁺μ^±e^±.     

Must the new heavy lepton have it's own neutrino?

We consider a minimal gauge theory of leptons, including only e, μ, the newly found charged lepton L and two massless two-component neutrinos.The model implies muon number non conservation. The present limit on μ+Nucleus→e+Nucleus leads to a branching ratio for μ→eγ not larger than 1.7 × 10^?12. Striking violations of μ?e universality in L decays are predicted.     

The discrepancy between τ and e + e − spectral functions revisited and the consequences for the muon magnetic anomaly

We revisit the procedure for comparing the π π spectral function measured in τ decays to that obtained in e ⁺ e ^? annihilation. We re-examine the isospin-breaking corrections using new experimental and theoretical input and find improved agreement between the τ ^?→π ^? π ⁰ ν _τ branching fraction measurement and its prediction using the isospin-breaking-corrected e ⁺ e ^?→π ⁺ π ^? spectral function, though not resolving all discrepancies. We recompute the lowest order hadronic contributions to the muon g?2 using e ⁺ e ^? and τ data with the new corrections and find a reduced difference between the two evaluations. The new tau-based estimate of the muon magnetic anomaly is found to be 1.9 standard deviations lower than the direct measurement.     

Contribution of the π<Superscript>0</Superscript>γ and ηγ intermediate states to vacuum polarization and the muon anomalous magnetic moment

Using new experimental data, we calculated, with a high precision, a contribution to the muon anomalous magnetic moment from the vacuum-polarization intermediate states π⁰γ and ηγ taking into account a correction for the trapezoidal rule: aμ(π⁰γ+aμ(ηγ)=(53.1± 1.5)×10^?11. We also determined a small contribution from the e⁺e^?π⁰, e⁺e^?η, and μ⁺μ^?π⁰ intermediate states, which was found to be equal to 0.5×10^?11.     

Non-standard Higgs bosons inSU(2)×U(1) radiative corrections

The 1-loop renormalization of theSU(2)×U(1) electroweak gauge theory with two Higgs doublets is performed in the on-shell scheme with finite self energies and vertices. Assuming different vacuum expectation values for the scalar doublets, which yield enhanced Yukawa couplings to fermions, we calculate the effects of the additional Higgs bosons in the radiative corrections to the leptonic processes:μ-decay,v _μ e-scattering, ande ⁺ e ^?→μ ⁺ μ ^?,τ ⁺ τ ^? with longitudinal polarization at PETRA and LEP/SLC energies. It is found that large effects occur in theM _W ?M _Z mass relation, the determination of sin² θ _w from \(\sigma (v_\mu e)/\sigma (\bar v_\mu e)\) and thee ⁺ e ^? forward-backward and polarization asymmetries, if either the charged Higgs or the additional neutral scalar/pseudoscalar are heavy. Enhancement effects and effects of light neutral bosons can better be observed in thee ⁺ e ^?→τ ⁺ τ ^? integrated cross section.     

Photon structure functions: Are they measurable?

It is shown that 3 of the 8 independent photon structure functions are simply calculable using leading logarithm techniques in QCD. We then discuss which of these are most readily measurable in the processese ⁺e^?→e⁺e^?+X,γp→μ ⁺ μ ^? X andμp→μμ ⁺ μμ ^? X. Detailed predictions are given for the latter processes including the case where beam and target are longitudinally polarised. Given sufficient beam intensities, the contributions from the anomalous (as opposed to vector meson-like) component of the photon structure function would be easily identifiable above the Bethe-Heitler pair production background. However, currently available beam intensities make such measurements impractical at present. We discuss simple algorithms for estimating the polarised and unpolarised quark and gluon distributions inside the proton and the hadronic (?-like) piece of the photon.     

Leptonic polarization asymmetries ate + e − colliders inE 6 theories

We examine the left-right and azimuthal polarization asymmetries of lepton pairs produced ine ⁺ e ^? ande ^? e ^? interactions as probes of new physics resulting fromE ₆ theories. The asymmetries are calculated and compared for the processese ⁺ e ^?→µ ⁺ µ ^?,e ⁺ e ^?→e ⁺ e ^?,e ^? e ^?→e ^? e ^?, ande ⁺ e ^?→L ⁺ L ^? whereL is either anE ₆ exotic, mirror, or fourth generation heavy lepton. Our results show that lepton polarization asymmetries can be used to easily distinguish differentE ₆ models and can be used to distinguish among possible new heavy leptonsL.     

Lepton charge and model of weak interactions with μ-e transitions

The gauge model of weak interactions is proposed and μ^±?e^? transitions predicted by the model are discussed. Estimates are given for μ^±→e^? transitions on hadrons like K⁺→π^?μ⁺e⁺ with Γ (K⁺→π^?μ⁺e⁺) ? 10^?11Γ(K⁺ and μ^? capture on nuclei with W(μ^?→e⁺) ? 10^?12W(μ^? → ν). Single μ^± production in e^? beams with a cross section δ ～ 10^?42?10^?41 cm² is predicted.     

Hard bremsstrahlung amplitudes fore + e − collisions with polarized beams at LEP/SLC energies

Cross sections are presented for the processese ⁺ e ^?→e ⁺ e ^?γ ande ⁺ e ^?→f \(\bar f\) γ (wheref is any light fermion) in the form of helicity amplitudes in which all complex phase information is kept. Owing to a spcial choice of the bremsstrahlung polarization and the use of spinor techniques the resultant expressions are extremely compact and lend themselves to fast numerical evaluation. An algorithm is given to obtain from the helicity amplitudes the cross section for arbitrary polarization of the incominge ⁺ e ^? beams. Special attention is given to the case of bremsstrahlung at very small angles to the beams, where a complicated dependence on the electron mass has to be taken into account.     

Effect of FCNC mediated <Emphasis Type="Italic">Z</Emphasis> boson on lepton flavor violating decays

We study the three body lepton flavor violating (LFV) decays μ ^?→e ^? e ⁺ e ^?, \(\tau^{-} \to l_{i}^{-} l_{j}^{+} l_{j}^{-}\) and the semileptonic decay τ→μφ in the flavor changing neutral current (FCNC) mediated Z boson model. We also calculate the branching ratios for LFV leptonic B decays, B _d,s →μe, B _d,s →τe, B _d,s →τμ and the conversion of muon to electron in Ti nucleus. The new physics parameter space is constrained by using the experimental limits on μ ^?→e ^? e ⁺ e ^? and τ ^?→μ ^? μ ⁺ μ ^?. We find that the branching ratios for τ→eee and τ→μφ processes could be as large as \({\sim}{\mathcal{O}}(10^{-8})\) and \(\mathrm{Br}(B_{d,s} \to \tau \mu,~ \tau e) \sim {\mathcal{O}}(10^{-10})\). For other LFV B decays the branching ratios are found to be too small to be observed in the near future.     

Radiative corrections in K→π ℓ + ℓ − decays

We calculate radiative corrections to the flavor-changing neutral current process K→π ? ⁺ ? ^?, both for charged and neutral kaon decays. While the soft-photon approximation is shown to work well for the muon channels, we discuss the necessity of further phase space cuts with electrons in the final state. It is also shown how to transfer our results to other decays such as η→γ ? ⁺ ? ^? or ω→π ⁰ ? ⁺ ? ^?.     

Testing weak neutral currents in longitudinally polarized colliding beams

We study the effects of a weak neutral current as they show up in longitudinally polarized colliding beams. The reactions considered here are e⁺e^?→μ⁺μ^? and e⁺e^?→π⁺π^?. The electromagnetic background and means to suppress this are also discussed.     

A search for anomalous contribution ine + e − →π 0/η γ annihilations

Data one ⁺ e ^?→η/π ⁰ γ collected by the Neutral Detector at Novosibirsk in a c.m. energy range up to 1.04 GeV have been studied with a purpose to single out of the scattering amplitude the triangle anomaly contribution predicted byqcd, pcac and Chiral Theories. We show that the cross section fore ⁺ e ^?→π ⁰ γ exhibits no sensitivity to theπ ⁰ triangle anomaly; instead, the cross section fore ⁺ e ^?→ηγ shows a clear sensitivity to the value of theη triangle anomaly and the best fit corresponds to a value for theη width in good correspondence with the world average value. It is also shown that the value of theρ→ηγ branching fraction is noticeably influenced by the existence of the anomaly. Finally, we give for the first time the absolute value for the hadronic phases of the vector mesons for the decay modesηγ andπ ⁰ γ.     

A measurement of the electromagnetic form factor of the eta meson and of the branching ratio for the eta Dalitz decay

In an optical spark chamber experiment we have obtained a sample of 80 eta Dalitz decays (η → e⁺e^?γ) and have measured the eta electromagnetic form factor to be F(X) = 1.0?(0.22 ±0.45)X, where X=M_ee²/M_η², and the branching ratio (η→e⁺e^?γ/(η→π⁺π^?π⁰)= (0.0082 ± 0.0020).     

Radiative asymmetry around the resonance in e+e−→μ+μ−

Under the assumption that the ψ is a pure 1^?? vector particle we have calculated the angular asymmetry in the process e⁺e^?→μ⁺μ^? around the resonance. We find that the asymmetry, calculated in the soft photon limit, becomes very small around the resonance.     

Spinless bosons in electron-positron annihilation

The contributions to the processes \(e^ + e^ - \to \mu ^ + \mu ^ - ,q\bar q,\gamma \gamma ,e^ + e^ - \) , mediated by scalar and/or pseudoscalar bosons are calculated. The constraints on their coupling constants and their masses are investigated as they arise from the radiative decayZ ⁰→⁺ e ^? γ and from the experimental data for the annihilation processes into lepton, photon and quark pairs. Data one ⁺ e ^?→μ⁺ μ^?, γγ ande ⁺ e ^? seriously reduce the domain of coupling constants to leptons and photons still allowed by the probable value of the width ofZ ⁰→e ⁺ e ^? γ. Experimentse ⁺ e ^?→μ⁺ μ^?, γγ,e ⁺ e ^? at 45 GeV c.m.s. energy with a sensitivity of 10% will decide about the existence of a heavy spinless boson with the presumed phenomenological couplings to leptons and photons. Assuming universality of the coupling to leptons and quarks a conservative bound on the contribution toR arising from spinless boson exchange is already in conflict with the presumed radiative width ofZ ⁰→e ⁺ e ^? γ.