Near-threshold radiative 3<Emphasis Type="Italic">π</Emphasis> production in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

We consider the π⁺π^?π₀γ final state in electron-positron annihilation at c.m.s. energies not far from the threshold. Both initial-and final-state radiations of the hard photon are considered, but without interference between them. The amplitude for the final-state radiation is obtained by using the effective Wess-Zumino-Witten Lagrangian for pion-photon interactions valid for low energies. In real experiments, energies are never so small that ρ and ω mesons would have a negligible effect. So a phenomenological Breit-Wigner factor is introduced in the final-state radiation amplitude to account for the vector mesons' influence. Using radiative 3π production amplitudes, a Monte Carlo event generator was developed which could be useful in experimental studies.     

Inclusive production of vector charmonium in two-photon <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

One of the processes involving the inclusive production of the vector-charmonium states J/ψ. and ψ(2S) in two-photon electron-positron annihilation at \(\sqrt s = 10.6 GeV\) is studied on the basis of the singlet model. Analytic expressions are derived for respective differential cross sections, and numerical values of the total cross sections are given, along with graphs that represent the distributions of cross sections in the scattering angle and in the vector-meson energy. It is shown that these distributions differ substantially from the analogous distributions for charmonium production in one-photon electron-positron annihilation. For this reason, the process under consideration can readily be isolated despite the smallness caused by an extra power of α.     

Two-photon production of vector resonance in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> collisions

A parameterization of the amplitude of the two-photon production of 1⁺⁺ and 1^?+ vector resonances V in the e ⁺ e ^? → e ⁺ e ^? V reaction has been obtained. The differential (in momentum transfer) scattering cross section dσ/dQ ² has been found for this reaction in the equivalent-photon approximation. The result obtained is model-independent.     

On <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> pair production by colliding electromagnetic pulses

Electron-positron pair production from vacuum in an electromagnetic field created by two counterpropagating focused laser pulses interacting with each other is analyzed. The dependence of the number of produced pairs on the intensity of a laser pulse and the focusing parameter is studied with a realistic three-dimensional model of the electromagnetic field of the focused wave, which is an exact solution of the Maxwell equations. It has been shown that e⁺e^? pair production can be experimentally observed when the intensity of each beam is I～10²⁶ W/cm², which is two orders of magnitude lower than that for a single pulse.     

Non-perturbative contribution to the thrust distribution in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

We re-evaluate the non-perturbative contribution to the thrust distribution in e ⁺ e ⁻→ hadrons, in the light of the latest experimental data and the recent NNLO perturbative calculation of this quantity. By extending the calculation to NNLO+NLL accuracy, we perform the most detailed study to date of the effects of non-perturbative physics on this observable. In particular, we investigate how well a model based on a low-scale QCD effective coupling can account for such effects. We find that the difference between the improved perturbative distribution and the experimental data is consistent with a 1/Q-dependent non-perturbative shift in the distribution, as predicted by the effective coupling model. Best fit values of α _s (91.2 GeV)=0.1164_−0.0026^+0.0028 and α ₀(2 GeV)=0.59±0.03 are obtained with χ ²/d.o.f.=1.09. This is consistent with NLO+NLL results but the quality of fit is improved. The agreement in α ₀ is non-trivial because a part of the 1/Q-dependent contribution (the infrared renormalon) is included in the NNLO perturbative correction. Address after 1 October 2008: Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford OX1 3NP, UK.     

Radioactive Production of the Lightest Neutralino in the Process of <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> Annihilation

The production of the lightest stable neutralino in the reaction with general mixing of the higgsino and gaugino is studied. General formulas for differential cross sections are presented. The dependence of the effective differential cross section on the photon energy spectrum and electron mass is illustrated together with the dependence of the effective total cross section on the beam energy for three different scenarios. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 48–57, June, 2005.     

Wavelet analysis of data in particle physics: Vector mesons in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

The advantages that wavelet analysis (WA) provides for resolving the structures in experimental data are demonstrated. Due to good scaling properties of the wavelets, one can consider data with various resolutions, which allows the resonances to be separated from the background and from each other. The WA is much less sensitive to noise than any other analysis and allows the role of statistical errors to be substantially reduced. The WA is applied to the e ⁺ e ^? annihilation into hadron states with quantum numbers of ρ and ω mesons, and to p-wave ππ scattering. Distinguishing the resonance structures from an experimental noise and the background allows us to make more reliable conclusions about the ρ′ and ω′ states. The WA yields a useful set of starting conditions for analysis of ω′ states with the multiresonance Breit-Wigner method preserving unitarity in the case of overlapping resonances. We also apply the WA for the ratio \(R_{e^ + e^ - } \).     

Investigation of the process <Emphasis Type="Italic">J/ψ</Emphasis> → <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> with the KEDR detector

The product of the electron width of the J/ψ meson and the probability for its decay to an electron-positron pair was measured by using data from the KEDR experiment at the VEPP-4M electron-positron collider. The result was Γ _ee × Γ _ee /Γ = 0.3392 ± 0.0068(stat.) ± 0.0063(syst.) keV.     

Parity-Violating in <Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript> Scattering at Finite Temperature

Parity violation implies that physics laws are not invariant under spatial coordinate reversal. Electron-positron scattering is a process that displays parity violation. Using the Thermo Field Dynamics formalism this scattering at finite temperature is analyzed. The transition amplitude is calculated as a function of temperature. The parity violation at very high temperatures tend to go to zero.     

Pseudoscalar Higgs boson in experiments at <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> colliders

The potential of experiments at e ⁺ e ^? colliders to search for a signal of a new pseudoscalar Higgs boson and to study its CP properties is analyzed. A new Higgs boson coupling to the b quark and τ lepton, which is parameterized in a model-independent way as m _b /v(a + iγ₅ b), is chosen to be an indicator of its CP nature. We study the e ⁺ e ^? → τ⁺τ^?vv, e ⁺ e ^? → b \(\bar b\)vv, and e ⁺ e ^? → e ⁺ e ^? b \(\bar b\) processes highly sensitive to anomalous Higgs boson couplings due to the dominant contributions from the vector boson fusion processes W*W* → H and Z*Z* → H in the central region. It is shown that the study of polarization of particles in the final state could help to separate the contributions from the scalar and pseudoscalar Higgs bosons. For instance, the consideration of the cascade decays of τ leptons in the e ⁺ e ^? → τ⁺τ^?vv process allows one to determine reliably the CP state of the Higgs boson as well as the value and the sign of the b parameter. As a result of our analysis, we develop a search strategy for a signal of a new pseudoscalar Higgs boson in future experiments at linear e ⁺ e ^? colliders, which will allow one to understand the CP nature of the Higgs boson and set the bounds on its couplings to fermions.     

Relative yield of charged and neutral heavy meson pairs in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation near threshold

The subject of the charged-to-neutral yield ratio for \(B\bar B\) and \(D\bar D\) pairs near their respective thresholds in e⁺e^? annihilation is revisited. As previously argued for the B mesons, this ratio should exhibit a substantial variation across the ?(4S) resonance due to interference of the resonance scattering phase with the Coulomb interaction between the charged mesons. A simple alternative derivation of the expression describing this effect is presented here, and the analysis is extended to include the D-meson production in the region of the ψ(3770) resonance. The available data on kaon production at the φ(1020) resonance are also discussed in connection with the expected variation of the charged-to-neutral yield ratio.     

Production of triply charmed Ω<Subscript>ccc</Subscript> baryonsin <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

The total and differential cross sections for the production of triply charmed Ω_ccc baryons in e⁺e^? annihilation are calculated at the Z-boson pole.     

Quark-hadron duality and production of charmonia and doubly charmed baryons in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> anninhilation

The cross sections for the production of charmonia and doubly charmed baryons in e ⁺ e ^? annihilation at an interaction energy of \(\sqrt s \) = 10.6 GeV are predicted under the assumption of quark—hadron duality. The method used is shown to remove some contradictions between experimental data and perturbative QCD.     

Unparticle Effects on Axion-Like Particles Production in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> Collisions

In this work, we study the effects of the vector unparticle on e⁺e^?→ γa processes. From the numerical results, we show that the cross-section with unparticle effects should be about 10¹⁴ ??10²³ times larger than the one without unparticle effects. This could have important implication for axion like particle searches in near future experiments.     

Measurement of cross sections for processes involving <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation to hadrons at the VEPP-2M collider

Results obtained by measuring, in experiments at the VEPP-2M e ⁺ e ^? collider with the CMD-2 and SND detectors at the Novosibirsk Institute of Nuclear Physics, cross sections for e ⁺ e ^? → hadrons annihilation processes at energies in the range 360 ≤ √s ≤ 1380 MeV are surveyed. The measured cross sections and the vector-meson parameters deduced from an analysis of these cross sections are presented. The cross section for the process e ⁺ e ^? → π ⁺ π ^? is compared with the spectral function for the decay τ ^? → π ^? π ⁰ ν _τ.     

Deviation from the standard model in the decay <Emphasis Type="Italic">π</Emphasis><Superscript>+</Superscript> → <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">νγ</Emphasis>

A precise investigation of radiative pion decay (π⁺ → e⁺νγ) in a pion beam from the meson factory of the Paul Scherrer Institute (Switzerland) was performed by the PIBETA Collaboration with the aid of the PIBETA detector. This resulted in finding 41 601 events of radiative pion decay in three kinematical regions. The absolute values of the branching ratio for radiative pion decay were determined in each of these regions. To a precision approximately four times higher than that known previously, the ratio of the axial-vector to the vector form factor was found to be γ ≡ F _A /F _V = 0.443 (15), the latter being fixed at F _V = 0.0259. The number of events found in the kinematical region specified by photon energies of E_γ > 55.6 MeV, positron energies of E _e > 20.0 MeV, and angles of θ_{γ, e} > 40° between the momenta of the corresponding particles (B region) was 5233. In region B, the measured branching ratio for radiative pion decay, R_π→evγ(expt) = 11.6(3) × 10^?8, proved to be smaller by eight standard deviations than that which follows from the Standard Model, R_π→evγ (theor) = 14.34(1) × 10^?8.     

One-loop electro-weak corrections to three-jet observables of <Emphasis Type="Italic">b</Emphasis>-quarks <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilations

We compute the full one-loop EW contributions of \({\mathcal{O}}(\alpha_{\mathrm{S}}\alpha_{\mathrm{EM}}^{3})\) entering the electron–positron into two b-quarks and one gluon cross section at the Z peak and LC energies. We include both factorisable and non-factorisable virtual corrections, photon bremsstrahlung but not the real emission of W ^± and Z bosons. Their importance for the measurement of α _S from jet rates and shape variables is explained qualitatively and illustrated quantitatively. Their impact on the forward–backward asymmetry is also analysed.     

One-loop electro-weak corrections to three-jet observables of <Emphasis Type="Italic">b</Emphasis>-quarks <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilations

We compute the full one-loop EW contributions of entering the electron–positron into two b-quarks and one gluon cross section at the Z peak and LC energies. We include both factorisable and non-factorisable virtual corrections, photon bremsstrahlung but not the real emission of W ^± and Z bosons. Their importance for the measurement of α _S from jet rates and shape variables is explained qualitatively and illustrated quantitatively. Their impact on the forward–backward asymmetry is also analysed. Work supported in part by the U.K. Science and Technology Facilities Council (STFC), by the European Union (EU) under contract MRTN-CT-2006-035505 (HEPTOOLS FP6 RTN) and by the Italian Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR) under contract 2006020509_004. An erratum to this article can be found at     

QCD Corrections to Squark Production in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> Annihilation in the MSSM with Complex Parameters

We discuss the pair production of scalar quarks in e ⁺ e ⁻ annihilation within the MSSM with complex parameters. We calculate the SUSY-QCD corrections to the cross section and show that the effect of the CP phases of these complex parameters on the cross section can be quite strong in a large region of the MSSM parameter space. This could have important implications for squarks searches and the MSSM parameter determination in future collider experiments. PACS number(s): 14.80. Ly, 12.60. Jv, 13.10. + q, 13.88. +e.