Electron dichroism effects in the relativistic (e, 2e) process for K-shell ionization of atoms

In this communication we present theoretical demonstration of electron dichroism in the relativistic (e, 2e) process for K-shell ionization of atoms in non-coplanar asymmetric geometry. The theoretical formalism has been developed in plane wave Born approximation and in this approximation the triple differential cross-section (TDCS) has been expressed as a product of kinematical factors and atomic structure functions. The longitudinal spin asymmetry in the relativistic (e, 2e) process on K-shell of atoms has been shown to depend on the interference between the transition charge and component of the transition current in the direction perpendicular to the scattering plane. Further, the longitudinal spin asymmetry has been shown to depend on incident electron energy, atomic number of the target, azimuthal angle of the ejected electron and scattered electron angle.     

Stokes parameters of γ-quanta in the e+ + e− → Z + γ reaction

A general analysis is made of the polarization properties of γ-quanta in the e⁺ + e^? → Z + γ reaction. Besides the standard mechanism of this reaction; which is determined by the eeZ interaction (neutral weak currents), the possible anomalous magnetic moment χ of the Z boson is also taken into account. A linear contribution in χ. to the differential cross section of the e⁺ + e^? → Z + γ process (with unpolarized particles in the initial and final states) leads to CP-odd asymmetry of the angular distribution of γ-quanta relative to the substitution cos Θ→?cos Θ, where Θ is the angle of emission of the γ-quantum relative to the electron. Measurement of this asymmetry with an accuracy of the order of 1% makes it possible to get a “sense” of the contribution of the magnetic moment of a Z boson of the order of 10^?3 GeV^?1.     

A measurement of the electroweak induced charge asymmetry in e+e−→bb̄

The forward-backward charge asymmetry for the process $\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{→}\text{b}\text{b}\text{?}\text{→ μ}{}^{\mathrm{\pm }}\text{+}$ hadrons has been measured using the JADE detector at PETRA. An asymmetry of (?22.8 ± 6.0 ± 2.5)% was observed at an average center of mass energy of 34.6 GeV. For comparison, an asymmetry of ?25.2% is expected on the basis of the standard Glashow-Salam-Weinberg model.     

Heavy vector mesons and the anomalous eμ events in e+e− annihilation

As a possible explanation of the SLAC anomalous eμ events, we computed the cross section for e⁺ + e^? → V⁺ + V^? → μ^± + e^± + neutrinos, taking into account the spin correlations of V^±. If one assumes that the vector meson has an anomalous magnetic moment (κ ≈ 1), the spin effects are considerable. The V^± production hypothesis seems to be a viable alternative to that of the heavy lepton production.     

On the interference betweenC-even andC-odd contributions to the reactione + e − →e + e − π+ π−

We calculate the interference between the bremsstrahlung and the photon-photon collision contributions to the differential cross-section ofe ⁺ e ^? →e ⁺ e ^? π⁺ π^?, for an experiment in which only one electron is tagged. The corresponding pion charge asymmetry has the same order of magnitude as the γγ cross-section in important parts of the phase space.     

Neutral weak currents in radiative e−e+ pair annihilation into a pair of arbitrary particles

The contribution of neutral weak currents (NWC) to the cross section for radiative annihilation of longitudinally polarized e^–e⁺ pairs into a pair of arbitrary particles is investigated. The possibilities for determining various structure functions, characterizing the process, and P-odd asymmetry and polarization, related to the presence of NWC, are investigated. The quantities indicated are estimated numerically for small departure angles of the photon relative to the axis of the e^–e⁺ beams.Translated from Izvestiya Vysshikh Uchebnykh Zavedneii, Fizika, No. 1, pp. 44–47, January, 1982.     

SU(2)×U(1) effects in e+e− annihilation: Generalized charge asymmetry

The observability of the SU(2)×U(1) electroweak charge asymmetry effects in e⁺e^? annihilation at $\text{s}\text{=29}\text{GeV}$ is addressed in the context of a Feynman-Field type fragmentation model. We assume three colors of five flavored quarks and one heavy lepton τ. We neglect, at this time, the hard gluon bremsstrahlung events. We take b→c+X as the b-decay mode and we assume all τ's and heavy hadrons decay within the resolution of the detector so thatonly light hadrons and leptons are detected. Allowing all these decays to occur, we then compute the expected front-back asymmetry of negatively charged particles weighted with zⁿ for z?0.0175, where n = 0.5, 1…, 7, 10, and z is the light-cone momentum fraction. We find, for example, that such an asymmetry is ≈5% for n=2for sin²θ_w=0.236 and Λ_{QCD=0.34 GeV}. In other words, due to the large number of charge particles produced per event, this SU(2)×U(1) charge asymmetry may be accessible experimentally in e⁺e^? → X already at PEP and PETRA energies.     

Width effects of theZ resonance and CP-violating asymmetry ine + e − annihilation

CP-violating rate asymmetry can be generated in a process only if its amplitude possesses an absorptive part. It is pointed out that such an absorptive part can be provided ine ⁺ e ⁻ annihilation by the presence of aZ(Z′) resonance of non-zero width. The CP asymmetry in the process , wherel _i are charged leptons, is discussed in several models. In a specific two-Z model, large and observable CP asymmetry ine ⁺ e ⁻ →τ ⁺ e ⁻ (τ ⁻ e ⁺) is shown to be possible at LEP/SLC energies.     

Model-independent analysis of Higgs spin and CP properties in the process \boldsymbol{e}^{+} \boldsymbol{e}^{-} \to\boldsymbol{t}\bar{\boldsymbol{t}} \boldsymbol{\Phi}

In this paper we investigate methods to study the $t\bar{t}$ Higgs coupling. The spin and CP properties of a Higgs boson are analysed in a model-independent way in its associated production with a $t\bar{t}$ pair in high-energy e ⁺ e ^? collisions. We study the prospects of establishing the CP quantum numbers of the Higgs boson in the CP-conserving case as well as those of determining the CP-mixing if CP is violated. We explore in this analysis the combined use of the total cross section and its energy dependence, the polarisation asymmetry of the top quark and the up-down asymmetry of the antitop with respect to the top–electron plane. We find that combining all three observables remarkably reduces the error on the determination of the CP properties of the Higgs Yukawa coupling. Furthermore, the top polarisation asymmetry and the ratio of cross sections at different collider energies are shown to be sensitive to the spin of the particle produced in association with the top-quark pair.     

Familon emissivity of dense e − e + plasma in an external magnetic field

Emission of a familon due to the processes e ^? → e ^?+φ and e ^? → μ ^?+φ by dense magnetized plasma is analyzed as a possible mechanism of energy and momentum losses by astrophysical objects. The field-induced effective familon-photon coupling in the familon-emission process is taken into account. The contribution of these processes to the familon emissivity of a magnetized plasma in a supernova explosion is calculated. It is shown that there is asymmetry of familon emission in the process e ^? → μ ^?+φ.     

Study of Δ(1232) isobar electroproduction at the VEPP-2M e + e − collider

Results from the Spherical Nonmagnetic Detector (SND) on Δ(1232) isobar electroproduction in the collisions of beam electrons (positrons) and residual gas nuclei in the VEPP-2M e ⁺ e ⁻ collider are presented. On the basis of the data obtained the expected counting rate of this process in future high-luminosity e ⁺ e ⁻ colliders (φ, c-τ, and b factories) is estimated. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 737–740 (25 May 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Signatures of thes-leptons andW,Z spins in polarized γe collisions

We study the gaugino +s-electron,Wv andZe photoproductions off electrons with both beams polarized. We make a systematic calculation of the spin and angular asymmetries and obtain model independent results, which allow to identify the spin and/or charge of the scalars-leptons and of the electroweak gauge bosons, either in the high energy limit or at the threshold. For example, the photon helicity asymmetries of theW andZ total cross sections have the distinct value 1 at threshold, but it is negative for the reactions γe→spinor + scalar. In the high energy limit, the same asymmetry for the differential cross sections is equal to one for spin zero boson and negative forW andZ photoproductions and Compton scattering.     

Interference of Electromagnetic and Weak Interactions at High Energies and Neutral-Current μe Universality

A review is given on three types of experiments which recently detected the interference of electromagnetic and weak interactions at high energies in the reactions eD₂ → eX (SLAC, 1979), e⁺e⁻ → μ⁺μ⁻ (PETRA/PEP, 1981–83) and μ±C→μ±X (BCDMS, 1982). Asymmetry formulae are explicitely derived using the quark-parton model and the SU(2) × U(1) standard theory. With particular emphasis on the deep inelastic muon scattering experiment, the corresponding experiments are described and their results summarized. Combined fits to the 1983 asymmetry and νe data verify completely the muon-electron universality of the weak neutral current interaction giving for the vector and axial-vector coupling constants v_e = 0.02 ± 0.06, a_e = −0.54 ± 0.03 (electrons) and v_μ = −0.05 ± 0.16, a_μ = −0.51 ± 0.05 (muons).     

Measurement of the generalized polarizabilities of the proton in virtual Compton scattering at MAMI

Virtual Compton scattering off the proton has been studied at Q ² = 0.33 (GeV/c)² at the MAMI accelerator in Mainz (Germany). The goal of the experiment is to measure the generalized polarizabilities (GPs) of the proton using the double polarized e p→e' p'γ reaction. This paper reports the measurement of the unpolarized photon electroproduction cross-section for the new data and the extraction of two linear combinations of GPs, which are essential for the analysis of the double spin asymmetry.     

Single and double spin asymmetries in the elastic <Emphasis Type="Italic">e</Emphasis>-<Emphasis Type="Italic">d</Emphasis> scattering and their dependence on the deuteron wave function

Single and double spin asymmetries in the elastic electron-deuteron (e-d ) scattering were investigated. The tensor-deuteron asymmetries T_2i(i = 0, 1, 2) and the beam-vector-deuteron asymmetries T ^e _1i(i = 0, 1) were calculated and compared with the available experimental data. The sensitivity of the results for these spin asymmetries to the deuteron wave function has been investigated. The predicted asymmetries were found to be agree with one another and with experiment. It was found that, the double spin asymmetry T ^e ₁₀ is much smaller than the T ^e ₁₁-asymmetry. Therefore, in addition to the single tensor-deuteron asymmetry T₂₀, the doubly beam-vector-deuteron asymmetry T ^e ₁₁ can be used as an another tool for extracting the deuteron electromagnetic form factors.     

Explaining GRB in the light of energy deposition rate for v+ [`(n)] \bar \nu → e+ + e? in a compact star

We have studied the v+ $ \bar \nu $ \bar \nu → e ⁺ + e ⁻ energy deposition rate near a rotating compact star which is important for the study of gamma ray bursts (GRB). The General relativistic (GR) and rotational effects increase the efficiency of the process immensely. The rotational effect also brings about an asymmetry in the deposition rate of the star.     

Measurement of e+e−→τ+τ− at high energy and properties of the τ lepton

The e⁺e^?→τ⁺τ^? process has been measured using the CELLO detector at a mean total centre of mass energy of 34.2 GeV using essentially all the decay channels of the τ lepton. The measured cross section yields R_τ=1.03±0.05 (stat)±0.07 (syst). Topological branching fraction are given for τ → 1, 3 or 5 charged tracks. The angular distribution shows a clear 1 + cos²θ dependance with a forward-backward asymmetry of -0.103 ± 0.052 corresponding to an axial-vector coupling a_τ of the τ to the weak neutral current given by a_τ=?1.12 ± 0.57.     

Hard photon next-to-leading corrections to two-fermion production in e + e − collisions above the Z 0 peak

A complete next-to-leading order calculation of the initial-state O (α) photonic corrections to hadron and lepton-pair production in e ⁺ e ^?. collisions is presented. The impact of the next-to-leading order corrections on the twofermion cross section and forward-backward asymmetry is studied in detail for several event selections, with special emphasis on hard photon effects at LEP1.5 and LEP2 energies. It is shown that for typical realistic event selections, initial-state next-to-leading order corrections in the soft approximation can be safely extrapolated to energies above the Z ⁰ peak without significant loss of precision.     

Analyzing thee + e −→e + e − angular distibution at LEP

The analysis of the lepton angular distribution at LEP is reviewed and the specific concerns in the case ofe ⁺ e ^– final state are singled out. Studies of the physical information contained in thee ⁺ e ^– angular distribution are shown to justify the need for a new approach. Two different solutions that enable the complete use of the angular distribution information for the extraction of theZ parameters are presented. We show that these approaches have accuracies well above the future experimental needs.