[en] An analysis is given of the QED factors relating the cross section for e e → e e X to the virtual 2-photon collision γ*γ* → X. Only transverse photons are considered, but no kinematical approximations are made. The cases where none, one or both of the scattered electrons are detected at angles >> msub(e)/E (E = beam energy) are separately considered. A full discussion is given of the kinematical restrictions necessary to arrive at factorisible Equivalent Photon Approximation formulae, and quantitative comparisons are given. Also discussed are the rapidity distribution of the produced system X and restrictions on the effective two-photon luminosity due to angular cuts on produced particles. (orig.)

[en] A test is made of the quark charges using the recently measured 2γ widths of the pseudoscalar (π⁰,eta,eta') and tensor (A₂,f,f') mesons. The model for GAMMAsub(γγ) is nonrelativistic quarkonium annihilation, including binding and SU(3) breaking corrections. The flavour mixing between the states (eta,eta',iota(1450)) or (f, f', THETA (1720)) is given by a linear quarkonium gluonium mass matrix which includes mass dependent SU(3) breaking corrections. For the pseudoscalars a fit is made to 5 experimental quantities sensitive to flavour mixing but independent of the quark charges. The best fit indicates a significant gluonium amplitude approx.= 0.6 in the eta'. The integral charge quark model is consistent with the measured value of GAMMAsub(γγ) (eta') only for the effective gluon masses <1.0 MeV/c² (95% C.L.). Corrections from radial excitations are discussed and it is concluded that a pure quarkonium radial excitation interpretation of the iota is unlikely. In the fractional charge model the measurements of GAMMAsub(γγ)(f,f',A₂) indicate that the f and f' are almost ideally mixed quarkonium states. In gauge integer charge models charged gluon annihilation may give large contributions to GAMMAsub(γγ)(f,f'). Such models are excluded by constraints from the strong decays f,f'->ππ, KK and the experimental upper limit on GAMMAsub(γγ)(THETA)BR(THETA->KK). Comparison of the fitted SU(3) breaking parameters with perturbative QCD expectations suggests Λ = 100 +- 50 MeV/c. (orig.)

[en] The current status, both theoretical and experimental, of two photon collision physics is reviewed with special emphasis on recent experimental results from e⁺e^- storage rings. After a complete presentation of the helicity amplitude formalism for the general process e⁺e^- → Xe⁺e^-, various approximations (transverse photon, Weisaecker Williams) are discussed. Beam polarisation effects and radiative corrections are also briefly considered. A number of specific processes, for which experimental results are now available, are then described. In each case existing theoretical prediction are confronted with experimental results. The processes described include single resonance production, lepton and hadron pair production, the structure functions of the photon, the production of high Psub(T) jets and the total photon photon cross section. In the last part of the review the current status of the subject is summarised and some comments are made on future prospects. These include both extrapolations of current research to higher energy machines (LEP, HERA) as well as a brief mention of both the technical realisation and the physics interest of the real γγ and eγ collisions which may be possible using linear electron colliders in the 1 TeV energy range

[en] I shall try as far as possible to confine myself to the material actually presented in the session, though in the case of f₀ production, and the important new evidence for hard subprocesses in sub(γ)sub(γ) collisions where I attempt a general survey of new data first shown at this conference some overlap with other Rapporteurs (Burke, Hilger, and Cords) is inevitable. I particularly emphasise special and (to me) interesting points that were raised in the discussion session, which because of time pressure were touched on only briefly by the other speakers. I make no attempt to give a comprehensive list of cross sections, sub(γ)sub(γ) widths of resonances etc. (orig./HSI)

No abstract available

[en] Optimised perturbation theory (OPT) is tested for a range of different physical quantities in QED and QCD. Successful applications of OPT in hard QCD processes give values of 1-2 GeV/c for the renormalisation scale μg. An effect on-shell scheme (OS) is proposed for QCD by fixing μ_R at ∼ 1.9 GeV within the MS renormalisation convention. The parameters of QCD in such a scheme are determined and the phenomenology of further tests is discussed. Heavy quark threshold effects in α_s(Q²) are described by the QCD analogue of a well-known QED formula. 63 refs., 24 figs., 3 tabs

[en] The problem of separating 1γ and 2γ processes is rediscussed in the light of new theoretical expectations of high psub(t) hadron production from jets in 2γ processes. Heavy lepton production is also considered and the conclusions are not so optimistic, particularly if several heavy leptons exist within the energy range of the machine. The author considers 3 potentially interesting fields of 2γ physics: (i) jet production, (ii) deep inelastic γγ scattering, (iii) production of C=+1 resonances. Experimental signatures are discussed and rates Tagging is also discussed, the main points being: a) Tagging efficiency, b) Backgrounds. Finally , single particle inclusive production of hadrons in various 1γ and 2γ processes are shown for different angular acceptance regions of a practical detector, and some features of a possible 2γ detector for LEP are summarized. (Auth.)

[en] The author considers the possibilities for the study of γγ interactions using the LEP storage ring. (HSI)

No abstract available

[en] An analysis is given of the QED factors relating the cross section for ee → eeX to the virtual 2-photon collision γ*γ* → X. Only transverse photons are considered, but no kinematical approximations are made. The cases where none, one or both of the scattered electrons are detected at angles >> msub(e)/E (E = beam energy) are separately considered. A full discussion is given of the kinematical restriction necessary to arrive at factorisible equivalent photon approximation formulae, and quantitative comparisons are given. Also discussed are the rapidity distribution of the produced system X and restrictions on the effective two-photon luminosity due to angular cuts on produced particles. (orig.)