Improving the equivalent-photon approximation in electron--positron collisions

The validity of the equivalent-photon approximation for two-photon processes in electron--positron collisions is critically examined. Commonly used forms to describe hadronic two-photon production are shown to lead to sizeable errors. An improved two-photon luminosity function is presented, which includes beyond-leading-logarithmic effects and scalar-photon contributions. Comparisons of various approximate expressions with the exact calculation in the case of the total hadronic cross section are given. Furthermore, effects of the poorly known low-Q2 behaviour of the virtual hadronic cross sections are discussed.Comment: 10 pages, Latex, uses 12pt.sty, no figur

Quarkonium production and decays

Quarkonium decays are studied in the charmonium model. Relativistic corrections, higher-order perturbative QCD corrections and non- perturbative contributions are discussed. Recent measurements of charmonium annihilation rates are used to evaluate the strong coupling constant $\alpha_s$ simultaneously with the wave functions (and their derivatives) at the origin. Further predictions are made for yet unobserved decay rates. The various models for quarkonium production in hadronic collisions are critically reviewed. Based on the charmonium model, the cross sections of different quarkonium states are given in a well-defined QCD perturbation series, including quark--antiquark, quark--gluon, and gluon--gluon scatterings. Numerical estimates are given for charmonium production in \p\p, \ppbar, and \pi\p collisions. The role of indirect \JP production via $\chi_{\c J}(1P)$, \eta_{\c}(2S), $\psi(2S)$ and \b-decays is pointed out. Relativistic effects and non-perturbative contributions are found to be important. Existing measurements are compiled and shown to be well explained if all contributions are included. The ${}^1S_0$ cross section is calculated in complete next-to-leading order. Finally, a study of the high-energy behaviour of quarkonium cross sections is made, based on the asymptotical behaviour of higher-order QCD corrections.Comment: 128 pages, compressed ps file available via anonymous ftp to darssrv1.cern.ch: cern/9402/th-7170-94.ps.Z, CERN-TH.7170/9

Quarkonium production: velocity-scaling rules and long-distance matrix elements

The hierarchy of long-distance matrix elements (MEs) for quarkonium production depends on their scaling with the velocity $v$ of the heavy quark in the bound state. Ranges for the velocities in various bound states and uncertainties of colour-singlet MEs are estimated in a quark-potential model. Different possibilities for the scaling with $v$ of the MEs are discussed; they depend on the actual values of $v$ and the QCD scale. As an application, J/psi polarization in e^+e^- annihilation is discussed. The first non-perturbative estimates of colour-octet MEs are presented and compared with phenomenological determinations. Finally, various predictions of prompt quarkonium production at LEP are compared.Comment: 17 pages, Latex, uses 12pt.sty and epsfig.sty, 2 figure

On the non-perturbative part of the photon structure function

We discuss a dispersion relation in the photon mass and show how (in principle) model-independent constraints on the parton distribution functions of the photon, notably a momentum sumrule, can be obtained. We present two sets of parametrizations, SaS~1 and~2, corresponding to two rather extreme realizations of the non-perturbative part. Inclusive electron scattering off a real photon is found to be insufficient to constrain the non-perturbative components. The additional sensitivity provided by the photon virtuality is outlined. Previous approaches to model the non-perturbative input distributions are commented upon.Comment: Latex, 7 page

Automatic pressure transducer calibration system

Systems and reliability engineering for automatic pressure transducer calibration syste

Model-independent QED corrections to photon structure-function measurements

We present the first calculation of QED radiative corrections to deep-inelastic electron-photon scattering in terms of those variables that are reconstructed in measurements of the photon structure function in electron-positron collisions. In order to cover the low-$Q^2$ region, we do not invoke the QCD-improved parton model but rather express our results in terms of the photon structure functions. Both analytical and numerical results are given.Comment: Latex, 8 pages, 3 figures, uses epsfig.sty, 12pt.st

A scenario for high-energy gamma-gamma interactions

A real photon has a complicated nature, whereby it may remain unresolved or fluctuate into a vector meson or a perturbative q-qbar pair. In gamma-gamma events, this gives three by three combinations of the nature of the two incoming photons, and thus six distinct event classes. The properties of these classes are partly constrained by the choices already made in our related gamma-p model. It is therefore possible to predict the energy-dependence of the cross section for each of the six components separately. The total cross section gives support to the idea that a simple factorized ansatz with a pomeron and a reggeon term can be a good approximation. Event properties undergo a stepwise evolution from p-p to gamma-p to gamma-gamma events, with larger charged multiplicity, more transverse energy flow and a higher jet rate in the latter process.Comment: 1+27 pages, LaTeX2e, 20 ps/eps figures included in file using filecontents environment

Central production of mesons: Exotic states versus Pomeron structure

We demonstrate that the azimuthal dependence of central meson production in hadronic collisions, when suitably binned, provides unambiguous tests of whether the Pomeron couples like a conserved vector-current to protons. We discuss the possibility of discriminating between q-qbar and glueball production in such processes. Our predictions apply also to meson production in tagged two-photon events at electron--positron colliders and to vector-meson production in ep collisions at HERA.Comment: 15 pages, latex, no figur

Models for Photon-photon Total Cross-sections

We present here a brief overview of recent models describing the photon-photon cross-section into hadrons. We shall show in detail results from the eikonal minijet model, with and without soft gluon summation.Comment: 7 pages, 5 figures, laTeX, requires espcrc2.sty. To appear in the Proceedings of Photon-99, Freiburg, 23 -27 May 99, labels in the figures 1,3,4,5 corrected, one typo in an equation correcte

Vector-Meson Electroproduction from Generalized Vector Dominance

Including destructively interfering off-diagonal transitions of diffraction-dissociation type, we arrive at a formulation of GVD for exclusive vector-meson production in terms of a continuous spectral representation of dipole form. The transverse cross-section sigma_T for gamma* p -> V p behaves asymptotically as 1/Q^4, while R_V = sigma_L/sigma_T becomes asymptotically constant. Contributions violating s-channel helicity conservation stay at the 10-15% level established in low-energy photoproduction and diffractive hadron--hadron interactions. The data for phi- and rho-meson production for 0 \lsim Q^2 \lsim 20 GeV^2 from HERA are found to be in agreement with these predictions.Comment: 16 pages, latex, 3 figure