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.     

Approximations for high-energy photon-photon scattering in two-photon processes and double bremsstrahlung

Presented are some approximation formulae for the processese ⁺ e ^? →e ⁺ e ^?γ^*γ^* →e ⁺ e ^?γγ (e ⁺ e ^?) scattering with intermediate γγ scattering) ande ⁺ e ^?→e ⁺ e ^?γγ (double bremsstrahlung) at high energies for forwarde ⁺ e ^? scattering, using not only the usual equivalent-photon approximation method but also direct approximations under certain kinematic conditions. In both cases the outgoing photons can be polarized. Their numerical check is examined by comparing these results with those of the exact calculations obtained in a recent paper. The agreement of both results is quite satisfactory if the required conditions are satisfied.     

A comprehensive description of the photon structure function and photon-photon total cross section data

We fit the photon structure function and photon-photon total cross section obtained from two photone ⁺ e ^? experimental data. We show that a combination of the QPM point-like cross section and an hadronic cross section, given by a simple energy power expansion modified by a threshold factor, is in excellent agreement with the data.     

Two-photon exchange in p⊆)p→ℓ+ℓ−X and a comparison with QCD

A thorough study of lepton-pair production from two-photon annihilation in p?)p collisions is presented. The differential cross section is calculated over a large range of energies (27?√s?800 GeV as a function of the dilepton mass M as well as the dilepton transverse momentum Q_T and the Feynman variable x_F. No kinematical approximations (such as the equivalent photon approximation) are made. For Q_T ≈ 0 the two-photon mechanism represents an important fraction of the pp→e⁺e^?X cross section already at ISR energies, whereas at ISABELLE energies it dramatically dominates in the interval 0?Q_T?1 GeV. At ISR energies these conclusions follow from a direct comparison of the two-photon contribution with pp→e⁺e^?X data. For the ISABELLE energy range the expected O(α_s) QCD contribution to pp→?⁺?^?X, corrected for soft gluon radiation to all orders (in leading bilogarithmic approximation), was taken as a reference. At larger Q_T and ISR energies the γγ contribution is negligible, whereas at √s = 800 GeV γγ/QCD? 10–20% almost everywhere. Furthermore, two-photon candidate events from the ISR are shown to be in reasonable agreement with theory. A decomposition of the γγ cross section into contributions from both proton vertices being elastic, inelastic and of mixed configuration is given. The results provide important clues for a future isolation of the two-photon mechanism.     

Peripherical processes in QED at high energies

In this review we consider the high energy processes in QED frames in peripherical kinematics. The key feature of this kinematics is that processes have a large cross section which do not decrease with the increasing of the initial center of mass energy. Two purposes to study peripheral processes are: the background processes with large total cross sections and the structure of jets in the fragmentation region.We describe the various QED peripherical processes in terms of Impact Factors and give the explicit expressions for the differential distributions and spin correlation effects, as well as estimates of the total cross section of peripheral processes in photon-photon, photon-lepton and lepton-lepton collisions.A special attention is paid to the small-angle Bhabha scattering process which is relevant for beam monitoring at LEP I, LEP II.Based on analytical properties of the amplitudes some relations (QED sum rules) between the high energy asymptotic of the cross sections of inelastic processes in e ⁺ e ^? collisions and higher order perturbative contributions to the electron Dirac and Pauli form-factors are derived.For practical using we present some loop momentum integrals.     

Tests of QED and elektroweak theories at PETRA

We review experimental results from PETRA on the reactions:e ⁺ e ^?→e ⁺ e ^?, μ⁺ μ^?, τ⁺ τ^?, and γγ at centre-of-mass energies up to 36.7 GeV. The data are compared with the predictions of quantum electrodynamics and electroweak theories. The implication of the total cross section measurements fore ⁺ e ^?→q \(\bar q\) →hadrons with respect to the weak mixing angle is discussed.     

Angular asymmetries ofe + e − annihilation to three jets

We discuss the angular asymmetries of 3-jet events ine ⁺ e ^? annihilation, originating from hard gluon bremsstrahlung off quarks. Lepton beam polarization helps to disentangle the various helicity components of the bremsstrahlung cross section. They are sensitive to the spin of the radiated quantum but are otherwise parameter-free.     

The production of neutral vector mesons by bremsstrahlung in electron-positron colliding beams

We study the bremsstrahlung production of the ? meson in the reaction e⁺e^? → e⁺e^?? (→ e⁺e^?π⁺π^?). This reaction gives a C = ?1 background which complicates the study of C = +1 two-photon processes at the new colliding-beam facilities. The cross section for the reaction rises from approximately 0.3 nb to 0.7 nb as the beam energy increases from 2 GeV to 15 GeV. From a study of the distributions of the final leptons and pions, we find a suitable choice of cuts which will reduce the event rate down to a small fraction of R. It is not possible to attribute the three-prong events seen at DELCO and PLUTO to this particular production mechanism.     

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.     

Search for large-rapidity-gap events in e+e− annihilation

We investigate the cross section for the production of a low-mass colour-singlet cluster ine ⁺ e ^? annihilation with a large rapidity gap between the colour-singlet cluster and the other jets. It is argued that such events are the cross-channel analogue of large-rapidity-gap events in deep-inelastic scattering, and therefore could in principle be used to investigate the analytic continuation of the BFKL pomeron to the positive-t kinematic regime, where one would expect the trajectory to pass through glueball states. The cross section can be calculated in perturbative QCD, so that the infrared scale arising from non-perturbative effects, which prevents an exponential fall-off with rapidity gap in the case of deep-inelastic scattering, is absent ine ⁺ e ^? annihilation. Correspondingly, the cross section for such events decreases rapidly with increasing rapidity gap.     

Initial-state radiation at LEP energies and the corrections to Higgs boson production

It is shown that for e⁺e^? scattering processes described by the exchange of one photon or vector boson the O(α) radiative corrections to the initial state completely factorize the lowest-order cross section. This factorization holds for both hard and soft (or virtual) photons. We present a formalism for applying these radiative corrections in a process-independent way, and described the corresponding computer program. As an application we study the initial-state radiative corrections to the Higgs production processes e⁺e^? → μ⁺μ^?H and e⁺e^? → e⁺e^?H.     

Weak radiative corrections to biphotonic pair annihilations

Neutral and charged current radiative corrections to e⁺e^? → γγ are computed in the Weinberg-Salam model. It is found that the charged current dominates the result and induces a ～ 1% percentage correction, neatly characterized by polarization effects. So e⁺e^? → γγ provides a clean test for weak radiative corrections.     

Production of unusual mesons in photon-photon collisions

The cross-section for the production of unusual mesons, such as (bc?) or (b?c), in photon-photon collisions is obtained in a high energy approximation. For a 100 + 100 GeV e⁺e^? collider, the cross section is estimated to be about one unit of R for (bc?) and (b?c).     

Z boson effects in electron positron scattering at epic energies at 14 GeV

We discuss the problem of testing the intermediate vector boson effects in the reactions e^?e⁺ → e^?e⁺ + hadrons, e^?e⁺ → e^?e⁺ + μ^?μ⁺, e^?p → e^?x with the next generation of accelerators, and conclude that these reactions must be considered. The differential cross sections for the one lepton at large four-momentum transfer are obtained, and a significant contribution of Z effects is found.     

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.     

Hard photon corrections for Bhabha scattering

Numerical results for the α³ differential cross section for e⁺e^? → e⁺e^? are presented for the case of e⁺e^? colliding beams. Special care is given to the hard photon corrections. Acoplanarity distributions for e⁺e^? → e⁺e^?γ are also presented. Attention is drawn to experimental conditions which require the calculation of still higher order corrections.     

The parton model,duality and deep-inelastic single-particle distributions

Within the quark parton model the two-component duality idea is generalized to single hadron inclusive distributions in deep-inelastic scattering. The discussion is limited to the current fragmentation region. The number of independent distribution functions is reduced. Relations as well as inequalities among the structure functions are obtained. In particular, the excess of π⁺ over π^? in the electroproduction off a proton comes out as a consequence and the differential cross section for e⁺e^? → π+ anything is fully determined by the electroproduction of pions on nucleons.     

Higgs-boson pairproduction ine + e − reactions

We calculate the production cross section of Higgs-boson pairs ine ⁺ e ^? annihilation. In this reaction the lowest order contribution comes from one loop graphs. We study the behaviour of the cross section as a function of the energy, the Higgs-boson mass and the scattering angle.     

Total and visible cross sections for multilepton events in e+e− collisions

We calculate cross section for e⁺e^? scattering into four-lepton final states such as e⁺e^?e⁺e^?, e⁺e^?μ⁺μ^?, μ⁺μ^?μ⁺μ^?, μ⁺μ^?τ⁺τ^?. We also give exclusive cross sectionsfor all cases where one or more lepton tracks are at large angles to the beams. The calculations are performed using a Monte Carlo event generator which takes into account the complete set of relevant lowest order Feynman diagrams.     

On the resummation of the α In2 z terms for QED corrections to deep-inelasticep scattering ande + e− annihilation

The resummation of the α ln² (z) non-singlet contributions is performed for initial state QED corrections. As examples, the effect of the resummation on neutral-current deep-inelastic scattering and thee ⁺ e ^? → μ⁺μ^? scattering cross section near theZ ^o-peak is investigated.