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: 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

Automatic pressure transducer calibration system

Systems and reliability engineering for automatic pressure transducer calibration syste

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

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

Analysis of superconducting electromagnetic finite elements based on a magnetic vector potential variational principle

Electromagnetic finite elements are extended based on a variational principle that uses the electromagnetic four potential as primary variable. The variational principle is extended to include the ability to predict a nonlinear current distribution within a conductor. The extension of this theory is first done on a normal conductor and tested on two different problems. In both problems, the geometry remains the same, but the material properties are different. The geometry is that of a 1-D infinite wire. The first problem is merely a linear control case used to validate the new theory. The second problem is made up of linear conductors with varying conductivities. Both problems perform well and predict current densities that are accurate to within a few ten thousandths of a percent of the exact values. The fourth potential is then removed, leaving only the magnetic vector potential, and the variational principle is further extended to predict magnetic potentials, magnetic fields, the number of charge carriers, and the current densities within a superconductor. The new element produces good results for the mean magnetic field, the vector potential, and the number of superconducting charge carriers despite a relatively high system condition number. The element did not perform well in predicting the current density. Numerical problems inherent to this formulation are explored and possible remedies to produce better current predicting finite elements are presented

Hybrid propulsion technology program: Phase 1. Volume 3: Thiokol Corporation Space Operations

Three candidate hybrid propulsion (HP) concepts were identified, optimized, evaluated, and refined through an iterative process that continually forced improvement to the systems with respect to safety, reliability, cost, and performance criteria. A full scale booster meeting Advanced Solid Rocket Motor (ASRM) thrust-time constraints and a booster application for 1/4 ASRM thrust were evaluated. Trade studies and analyses were performed for each of the motor elements related to SRM technology. Based on trade study results, the optimum HP concept for both full and quarter sized systems was defined. The three candidate hybrid concepts evaluated are illustrated

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

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