Effect of weak neutral currents in the process e− + p → e− + γ + X

Polarization effects in the inclusive process e^– + p e^– + + X due to the neutral current are studied in the framework of the Weinberg-Salam model. Expressions for the asymmetry parameters and the degree of circular polarization of the photons are obtained in the quark-parton picture. It is shown that measurement of such quantities gives additional information about the quark structure of the hadronic weak neutral current.Paper presented at the scientific session of the nuclear physics branch, USSR Academy of Sciences and the Moscow State University on Electromagnetic and Weak Interactions (Moscow, January 16–20, 1979).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 96–99, January, 1981.     

Proc ess es e+ e− → cccc and e+ e− → J/ψ + gg at $$\sqrt s = 10.59 G eV$$

Experimental data obtained by the BELLE Collaboration for inclusive J/ψ production in the processes e⁺e^? → J/ψ + gg and e⁺e^? → J/ψ + cc are discussed. These data are compared with the predictions of perturbative QCD that were obtained by two methods, that which employs information about the J/ψ wave function and that which relies on the hypothesis of quark-hadron duality exclusively. Both computational methods yield results that disagree with the experimental data considerably. The dependence of the cross section for the process e⁺e^? → J/ψ + gg on the effective gluon mass is studied. The cross section for the production of doubly charmed baryons Ξ _cc ^* is estimated.     

The process e + e − → ωπ0 near the Φ resonance

The reaction e ⁺ e ^?→ωπ⁰ near a Φ resonance was studied with a spherical neutral detector at VEPP-2M e ⁺ e ^? collider. Both main modes of decay of a ω meson were investigated: ω→π⁺π^?π⁰ and ω→π ⁰γ. The probability of decay Φ→ωπ⁰ was obtained from the magnitude of the interference wave in the cross section for the reaction e ⁺ e ^?→ωπ⁰→ π⁺π^?π⁰π⁰: B(Φ→ωπ⁰) = (5.5 _?1.4 ^+1.6 ±0.3) ×10^?5. The ratio of the partial widths of the ω meson was obtained from the ratio of the cross sections for the two modes: Γ(ω→π⁰γ )/Γ(ω→π⁺π^?π⁰) = 0.0994 ± 0.0036 ± 0.0038.     

Electroweak radiative corrections to e+e− → Z0Z0

The cross section for e⁺e⁻ → Z⁰Z⁰ with arbitrary polarizations of the leptons and bosons is calculated in the standard electroweak model including the complete one-loop virtual and soft-photon bremsstrahlung corrections. All necessary analytical formulas are presented; numerical results are discussed for the unpolarized case and for the polarization asymmetry. At LEP 200 energies the weak corrections are dominated by the self-energy of the external Z⁰-bosons which contributes about +15%. With increasing energy, the weak corrections decrease up to -18% at 1 TeV due to other contributions.     

Energy dependence of e + e − → 6π and e + e − → N\bar N cross sections near N\bar N the threshold

Using recent BABAR, CMD-3 and SND data, the sum of e ⁺ e ^? → 3(π⁺π^?), 2(π⁺π^?π⁰), \(p\bar p\) , \(n\bar n\) cross sections is obtained. Unlike e ⁺ e ^? 3(π⁺π^?) and e ⁺ e ^? → 2(π⁺π^?π⁰) processes, no structures in total cross section are found near the \(N\bar N\) threshold within the limits of measurement errors.     

Search for the e + e − → K ± K S π ∓ process on the VEPP-2M e + e − collider

We report on the results of the search for the e ⁺ e ^? → K ^± K _S π ^? process. Data with an integrated luminosity of 1.36 pb^?1 collected in experiment with a spherical neutral detector (SND) on the VEPP-2M e ⁺ e ^? collider in the energy range from 1.36 to 1.38 GeV have been analyzed. The upper limits of the σ < 150 pb cross sections of the sought process have been established for an energy of 1.37 GeV at a confidence level of 90%.     

Short-distance CP-violating contributions to the KL→π0e+e− decay

New constributions to the K_L→π⁰e⁺e⁻ amplitude are presented. Short-distance penguin induced diagrams for the s→dγ¹ transition supplement the previously considered electromagnetic penguin. The new CP-violating amplitude corresponds to a new piece of the relevant anomalous dimension matrix. Strong interaction corrections to the new part of the effective hamiltonian are calculated in the leading logarithmic approximation. The role of subleading terms is also discussed.     

Measurement of the ω, ρ → π0 e + e − branching fractions

The e ⁺ e ^? → ω, ρ → π⁰ e ⁺ e ^? processes have been investigated in the experiments with Spherical Neutral Detector at the VEPP-2M e ⁺ e ^? collider. The measurements provide the probability ?(ω → π⁰ e ⁺ e ^?) = (0.761 ± 0.053 ± 0.064) × 10^?3 of the ω → π⁰ e ⁺ e ^g- conversion decay and the upper limit ?(ρ → π⁰ e ⁺ e ^?) < 1.2 × 10^?5 (at 90% CL) for the ρ → π⁰ e ⁺ e ^? decay. The transition form factor was measured at three values of the 4-momentum transfer squared.     

Is there a puzzle in the π0→e + e − decay?

We show the importance of precise experimental cuts in π⁰→e ⁺ e ^? decay measurements. Similar cuts have little effect in η(K _L ⁰ )→μ⁺μ^? decays.     

Comparative study of Z′ searches in e+e− and e−e− scattering

We consider indirect searches for additional neutral vector bosons in e⁺e⁻ and e⁻e⁻ collisions, and compare these two linear collider modes with similar analysis procedures and assumptions. Discovery limits and resolving power are discussed in a model-independent way.     

Study of the K − → e − νπ 0 decay

The decay K ^? → e ^? νπ ⁰ has been studied using in-flight decays detected with the ISTRA₊ setup working at the 25-GeV negative secondary beam of the U-70 PS. About 130K events were used for the analysis. The λ ₊ parameter of the vector form factor has been measured: λ ₊=0.0293±0.0015(stat.)±0.002(syst.). The limits on the possible tensor and scalar couplings have been derived: f _T/f ₊(0)=?0.045±0.060(stat.) and f _S/f ₊(0)=?0.019 _?0.016 ^+0.025 (stat.).     

Jet masses in e+e− annihilation

We calculate heavy (M _H ² /s) and light (M _L ² /s) jet masses up toO(α _s ² ) in perturbative Quantum Chromodynamics (QCD). The sensitivity of these quantities to radiative corrections, quark masses, fragmentation effects as well as their infrared stability properties, are investigated and compared to those exhibited by other jet measures. A comparison with recent Mark II data is also presented.     

Possibility of distinguishing the contribution of neutral weak currents in e+e− → μ−μ+ experiments with transverse-polarized clashing beams

The process e⁺+e^{– –}+ ⁺ 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. Arbitrary polarizations of all the particles are taken into account simultaneously. Polarization effects are analyzed in detail for the case of transverse-polarized clashing beams, and various possibilities for distinguishing the contribution of neutral weak currents are identified. This possibility is very important not only for obtaining information about the structure of these currents but also for experimentally determining the sign of the weak-interaction constant. Calculations show that the neutral weak currents lead to significant polarization effects at attainable energies. These effects are very sensitive to the model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 22–27, April, 1978.The authors thank A. A. Sokolov for interest and a useful discussion.     

The process e + e − → bb̅W + W − at the next linear collider in the Minimal Supersymmetric Standard Model

The complete matrix element for e ⁺ e^? → bb?W⁺ W^? is computed at tree-level within the Minimal Supersymmetric Standard Model. Rates of interest to phenomenological analyses at the Next Linear Collider are given. In particular, we study:

• ? tt? production and decay tt? →(bW ⁺)(b?W ^?)
• ? ZH production followed by Z → bb? and H → W ⁺ W^?
• ? AH production followed by A→ bb? and H → W ⁺ W^?
• ? hW ⁺ W^? production followed by h→ bb?.

Top and Higgs finite width effects are included, as well as all those of the irreducible backgrounds.     

Thrust ine + e −-annihilation

The thrust distribution ine ⁺ e ^–-annihilation is analysed in perturbative QCD. Proper account is taken of multiple emission of gluons. Scaling holds for this quantity in the sense that its energy dependence comes only through the change in the QCD effective coupling. It thus provides an ideal means to determine the value of the QCD mass scale experimentally. From the data atW=91 GeV by the ALEPH collaboration at LEP, we obtain .     

Duality ine + e − annihilation

With the help of a relativistic generalization of the formula for the leptonic width of quarkonium in the semiclassical approximation it is shown that for any confinement potential nonsingular at the origin the sum of total cross sections for the production of the heavy quarkonium states \((Q\bar Q)_n\) with masses \(M_n \leqq \sqrt s\) ine ⁺ e ^?-annihilation is equal to the cross section at givens for the production of the free quark-antiquark pair \(Q\bar Q\) . We obtain also a family of dual sum rules for quarkonium which are in agreement with the available experimental data on charmonium and beautionium within experimental errors.     

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

The process e⁺e^{– – +} 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.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 31–36, April, 1978.The authors thank A. A. Sokolov for a useful discussion and for interest in this work.