Charm production at HERA

The ZEUS data on the charm structure function F_2^c at small x fit well to a single power of x, corresponding to the exchange of a hard pomeron that is flavour-blind. When combined with the contribution from the exchange of a soft pomeron, the hard pomeron gives a good description of elastic $J/\psi$ photoproduction.Comment: 6 pages, plain tex, with 3 figures embedded using epsf. Typos corrected in equations (10) and (11

Exclusive Vector Photoproduction: Confirmation of Regge Theory

Recent small-t ZEUS data for exclusive rho photoproduction are in excellent agreement with exchange of the classical soft pomeron with slope alpha'=0.25 GeV^{-2}. Adding in a flavour-blind hard-pomeron contribution, whose magnitude is calculated from the data for exclusive J/psi photoproduction, gives a good fit also to the ZEUS data for rho photoproduction at larger values of t, and to phi photoproduction.Comment: 6 pages, plain tex, with 5 figures embedded using eps

Does the hard pomeron obey Regge factorisation?

While data for the proton structure function demand the presence of a hard-pomeron contribution even at quite small Q^2, previous fits to the pp and p\bar p total cross sections have found that in these there is little or no room for such a contribution. We re-analyse the data and show that itmay indeed be present and that, further, it probably obeys Regge factorisation: sigma^{gamma p}(s,Q_1^2)sigma^{gamma p}(s,Q_2^2)= sigma^{pp}(s)sigma^{gamma gamma}(s,Q_1^2,Q_2^2) for all values of Q_1^2 and Q_2^2.Comment: 11 pages, 10 figure

Light Vector Meson Spectroscopy

The current situation for vector meson spectroscopy is outlined, and it is shown that the data are inconsistent with the generally-accepted model for meson decay. A possible resolution in terms of exotic (hybrid) mesons is given. Although this hypothesis resolves some of the issues, fresh theoretical questions are raised. It is argued that high-precision $e^+e^-$ annihilation data provide an excellent laboratory for studying many aspects of nonperturbative QCD.Comment: Paper T05 presented at the Workshop on e+e- Physics at Intermediate Energies, SLAC, May 200

Unusual high-pT jet events at HERA

We calculate the cross-section for events at HERA where the proton loses only a minute fraction of its initial energy, all of which goes into producing a single pair of transverse jets.Comment: 4 pages plus figure

The Interest of Large-t Elastic Scattering

Existing data for large-$t$ $pp$ elastic-scattering differential cross-sections are energy-independent and behave as $t^{-8}$. This has been explained in terms of triple-gluon exchange, or alternatively through triple-singlet exchange. A discussion is given of the problems raised by each of these explanations, and of the possibility that at RHIC or LHC energies the exchange of three BFKL pomerons might result in a rapid rise with energy.Comment: 6 pages, plain tex, 3 figures embedded with eps

Perturbative Evolution and Regge Behaviour

The known analytic properties of the Compton amplitude at small $Q^2$ place significant constraints on its behaviour at large $Q^2$. This calls for a re-evaluation of the role of perturbative evolution in past fits to data.Comment: Revised figures 4 and

Systematic Regge theory analysis of omega photoproduction

Systematic analysis of available data for $\omega$-meson photoproduction is given in frame of Regge theory. At photon energies above 20 GeV the $\gamma{+}p{\to}\omega{+}p$ reaction is entirely dominated by Pomeron exchange. However, it was found that Pomeron exchange model can not reproduce the $\gamma{+}p{\to}\rho{+}p$ and $\gamma{+}p{\to}\omega{+}p$ data at high energies simultaneously with the same set of parameters. The comparison between $\rho$ and $\omega$ data indicates a large room for meson exchange contribution to $\omega$-meson photoproduction at low energies. It was found that at low energies the dominant contribution comes from $\pi$ and $f_2$-meson exchanges. There is smooth transition between the meson exchange model at low energies and Regge theory at high energies.Comment: 7 pages, 8 figures, revtex