Neutral Current Effects Research Articles

Neutral current effects for e +e − → ℓ +ℓ − around vector resonances

We present a complete analysis of the forward-backward asymmetry as well as of the longitudinal polarization of the outgoing lepton in the processes e +e − → ℓ +ℓ −, around the energy of a vector meson resonance (ϒ, T, …). Both effects manifest a strong energy-dependent structure near the mass of the resonance due to the interference with the background. These observables are carefully studied near the ϒ peak. Furthermore, the effects of possible vector mesons of higher mass, below and above the Z 0, are also considered.

W0effects in electron-positron collisions on1−resonances

Cross sections are given for ${e}^{\ensuremath{-}}{e}^{+}$ collisions on ${1}^{\ensuremath{-}}$ resonances producing pairs of spin-\textonehalf{} particles in the tree approximation. Effects of neutral currents and beam polarization are included. Possibilities for measuring ${W}^{0}$ effects in collisions producing ${\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}$, ${\ensuremath{\tau}}^{\ensuremath{-}}{\ensuremath{\tau}}^{+}$ and ${e}^{\ensuremath{-}}{e}^{+}$ at the $\ensuremath{\Upsilon}$ and higher-mass resonances are discussed.

Neutral-current effect in lepton pair production with polarized photons

We have investigated the parity-violating asymmetry for the lepton pair production with circularly polarized photons. Numerical calculations are given in the Weinberg-Salam model.

Parity-Violating Asymmetry in Lepton Pair Production with Circularly Polarized Photons

The neutral-current effects in the lepton pair production with circularly polarized photon beams have been investigated in unified gauge theories. We derive the parity-violating asymmetry of leptons produced by right- and left-handed photons. Numerical calculations are given for the proton and isoscalar targets in the Weinberg-Salam model. The asymmetry is shown as a function of the lepton energy in some kinematical configurations. We find the parity-violating effects are of the order of w-• for the incident photon energy of 20 Ge V.

The rho -exchange isovector parity-violating potential

It is shown that the rho -exchange isovector parity-violating potential is constrained by PCAC to be much weaker than the pi -exchange potential, and much weaker than recently proposed by Galic et al. (1979). This potential does not therefore provide a mechanism for suppressing enhanced neutral-current effects in the pi -exchange potential.

Internal conversion as a probe of weak neutral currents

Weak neutral-current effects in the internal conversion process are considered. The $K$, ${L}_{\mathrm{I}}$, and ${L}_{\mathrm{II}}$ conversions of $M1$ decays are shown to be uniquely sensitive to the nucleon-axial-vector-electron-vector coupling. Parity violating effects are calculated as a function of the atomic charge and nuclear transition energy and are shown to be \ensuremath{\sim}${10}^{\ensuremath{-}6}$ in favorable cases. Several possible experiments are discussed, as is the estimation of the required nuclear matrix elements.

Discrete symmetries, natural flavor conservation and weak mixing angles

Through their physically relevant representations, I characterize the class of finite symmetry groups insuring natural conservation of all quark flavors in neutral current effects, in generalized Weinberg-Salam models. As pointed out by Gatto, Morchio and Strocchi, these situations lead to a natural determination of all the generalized Cabibbo angles. A necessary and sufficient condition for avoiding a trivial generalized Cabibbo matrix is also given.

Effects of weak neutral currents in e?e+ ? N*�N*

Effects of weak neutral currents in e?e+ ? N*�N*

Neutral current effects in muonic atoms: E1-E2 interferences

We study the parity-violating neutral current effects in muonic atoms which might result from an interference between E1 and E2 amplitudes in 3D → 1S transitions. We conclude that polarization asymmetries may be measurable in heavy atoms (Z ~ 70) exhibiting large nuclear deformations.

A left-right symmetric model with a useful global symmetry

A simple left-right symmetric model is presented in which a global symmetry prevents neutrinos from acquiring a mass, avoids flavor changing neutral current effects and predicts the existence, in one case, of an absolutely stable quark or lepton.

Hard Photon Correction to e+e- -> + - and Effects of Neutral Weak Current

Taking account of the neutral current effects within the Weinberg-Salam model, we derive the formulae for the total cross-section of e+e- →µ+µ-, the energy spectrum of the photons emitted in e+e- →µ+µ-γ and the hard photon correction to the cross-section of e+e- →µ+µ-, which represent the generalization of QED formulae. Numerical estimates for the contributions of the neutral current effects to the processes at very high energies are also given. The asymptotic formulae at extremely high energy are derived for the hard photon corrections as well as for the energy spectrum of the photons.

Large Parity Admixture inNe21?

In $^{21}\mathrm{Ne}$ there are two levels of the same spin and opposite parity separated by 8 keV. This suggests that a parity-nonconserving nucleon-nucleon potential will give rise to large parity admixtures in these states. In our calculation the standard Cabibbo parity-nonconserving potential gives a circular polarization of at least ${10}^{\ensuremath{-}3}$ for the 2.79-MeV transition ${\frac{1}{2}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\frac{3}{2}}^{+}$ ground state. Strong neutral-current effects would lead to ${P}_{\ensuremath{\gamma}}$ in excess of 1% in contradiction with a recent experiment.

Neutral-current effects ine+e−→τ+τ−on aψ-like resonance

We suggest that the reaction ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ on a $\ensuremath{\psi}$-like resonance may provide a method for testing theories of the weak neutral current. The method is based on the observation that the $\ensuremath{\tau}$ decay products from this reaction will have a forward-backward asymmetry induced by the polarization sensitivity of the $\ensuremath{\tau}$ decays. We point out that, to the extent that the $\ensuremath{\psi}$-like resonance stands above background, this reaction provides not only an improved counting rate but also relief from the radiative asymmetries that trouble proposals to measure neutral-current asymmetries in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$.

Possibility of distinguishing the effect of neutral weak currents in e+e? ? ???+ experiments with longitudinally polarized clashing beams

The process e+e− →μ − μ + for the case of longitudinal polarization of the initial and final particles is studied on the basis of several models: the Weinberg-Salam model, the Lee-Prentki-Zumino model, the vector model, the X model, and under the assumption of a V-A structure of the neutral weak currents. Polarization effects tn the differential and total cross sections for this process are analyzed in detail, and various possibilities for distinguishing the contribution of neutral weak currents are found. Calculations show that neutral weak currents lead to appreciable polarization effects at attainable energies and that these effects are very sensitive to the model. It is important to note that an experimental study of these effects can yield valuable information on not only the structure of the neutral weak currents but also the sign of the weak-interaction constant.

Search for Neutral-Weak-Current Effects in the NucleusF18

The circular polarization of the $\ensuremath{\gamma}$ rays from the 1.08\ensuremath{\rightarrow}0.0 MeV transition of $^{18}\mathrm{F}$ has been measured to be (-0.7 \ifmmode\pm\else\textpm\fi{} 2.0) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$, a value significantly smaller than predicted by recent calculations which include the effects of neutral weak currents.

Higher-order effects in Fermi-type charged current theory of weak interactions: Semi-leptonic neutral currents

In a convergent field theory rescattering graphs lead to neutral-current effects of the observed magnitude if the effective cut-off momentum is ∼G − 1 2 ≈ 300 GeV . A perturbation expansion is justified owing to the value f=0.18 of the resulting expansion parameter.

Neutral-current effects in Bethe-Heitler pair production

We consider Bethe-Heitler pair production in which the exchanged photon is replaced with a neutral weak intermediate boson. The interference between this and the pure Bethe-Heitler amplitudes contributes to an asymmetry between the lepton pairs and, in addition, the leptons acquire a finite longitudinal polarization. Both effects are calculated and numerical examples are given in the standard Weinberg-Salam model.

Neutral-current effects in elastic charged-lepton-nucleon scattering

The possibility of observing weak-neutral-current effects in the elastic scattering of charged leptons from nucleons is discussed. General features of different possible polarization experiments (including the possibility of testing for second-class neutral currents) are considered. Polarization asymmetries are calculated for polarized-(lepton)-beam and polarized-target experiments under a wide range of kinematic conditions and for several different gauge models. The desirability of doing these experiments at moderate, rather than very large, momentum transfers is emphasized.

Dilepton production in PP and [formula omitted]P collisions as a probe to the nature of the neutral current interaction

The dilepton production and the asymmetry parameters in PP and P P collisions including the effects of neutral currents are calculated in the SU L(2) × SU R(2) × U L+R(1) theory. Distinctions from the predictions of the SU(2) L × U(1)-theory are noted.

Rare muon decays, heavy leptons, andCPviolation

We generalize and elaborate a model recently proposed by Cheng and Li. It is characterized by the breakdown of separate conservation laws for e and ..mu.. lepton types and allows for such processes as ..mu.. ..-->.. e + ..gamma.., ..mu.. ..-->.. 3e. Our generalization incorporates the singly charged heavy lepton discovered in e/sup +/e/sup -/ colliding-beam experiments, and it opens up the possibility of introducing CP-violating effects in lepton reactions. We analyze the ..mu.. ..-->.. 3e decay process, both with respect to rate (relative to ..mu.. ..-->.. e + ..gamma..) and spectrum, including CP-violating correlations. Other physically interesting features are also discussed for the generalized scheme: neutrino ''sharing'' and off-diagonal neutral-current effects.