Phenomenological description of the gamma* p cross section at low Q2

Low Q2 photon-proton cross sections are analysed using a simple, QCD-motivated parametrisation $\sigma_{\gamma^\star p}\propto 1/(Q^2+Q_0^2)$, which gives a good description of the data. The Q2 dependence of the gamma* p cross section is discussed in terms of the partonic transverse momenta of the hadronic state the photon fluctuates into.Comment: 14 pages, revtex, epsfig, 2 figure

Deep Inelastic Scattering at HERA

Results from the H1 and ZEUS experiments at HERA on deep inelastic scattering are reviewed. The data lead to a consistent picture of a steep rise in the F_2 structure function and in the gluon density within the proton. Important new information on the partonic structure of diffraction is emerging from H1 and ZEUS. The space-like region in which the weak and electromagnetic interactions become of equal strength is being explored for the first time. A possible excess of events at high x and Q^2 compared to the expectations of the Standard Model has been observed in both experiments.Comment: 80 pages, 42 figure

Spectroscopy at B-factories Using Hard Photon Emission

The process of hard photon emission by initial electrons (positrons) at B-factories is discussed. It is shown that studies of the bottomonium spectroscopy will be feasible for the planned integrated luminosity of the B-factory experiments.Comment: 9 pages, Latex, 1 fugure, Submitted to Int.Jour.Mod.Phys.

Vector Meson Production in the Golec-Biernat Wuesthoff Model

We apply the Golec-Biernat Wuesthoff model in the calculation of vector meson photo- and electroproduction. Starting from very simple non-relativistic wave functions we show that the model provides a good description of $J/\Psi$ cross sections in wide $Q^2$ and $W$ ranges. For the light mesons one obtains the approximately correct $W$ dependence and ratio of longitudinal to transverse cross sections, although in this case the normalization, affected mainly by the wave function employed, is not in good agreement with data

Implications of Hadron Collider Observables on Parton Distribution Function Uncertainties

Standard parton distribution function sets do not have rigorously quantified uncertainties. In recent years it has become apparent that these uncertainties play an important role in the interpretation of hadron collider data. In this paper, using the framework of statistical inference, we illustrate a technique that can be used to efficiently propagate the uncertainties to new observables, assess the compatibility of new data with an initial fit, and, in case the compatibility is good, include the new data in the fit.Comment: 22 pages, 5 figure

A characteristic plot of pomeron-exchanged processes in diffractive DIS

The dependence of the fractal behaviors of the pomeron induced system in deep inelastic lepton-nucleon scattering upon the diffractive kinematic variables is found rather robust and not sensitive to the distinct parameterization of the pomeron flux factor and structure function. A feasible experimental test of the phenomenological pomeron-exchanged model based on the fractal measurement in DESY $ep$ collider HERA is proposed.Comment: 14 pages, 2 Postscript figure

The Pomeron In Exclusive Vector Meson Production

An earlier developed model for vector meson photoproduction, based on a dipole Pomeron exchange, is extended to electroproduction. Universality of the non linear Pomeron trajectory is tested by fitting the model to ZEUS and H1 data as well as to CDF data on $\bar pp$ elastic scattering.Comment: 12 pages, 13 figure

Soft Photoproduction Physics

Several topics of interest in soft photoproduction physics are discussed. These include jet universality issues (particle flavour composition), the subdivision into event classes, the buildup of the total photoproduction cross section and the effects of multiple interactions.Comment: 10 pages, LaTeX2e, no figures, to appear in the proceedings of the Durham Workshop on HERA Physics, ``Proton, Photon and Pomeron Structure'', 17--23 September 1995, Durham, U.

Interference in Exclusive Vector Meson Production in Heavy Ion Collisions

Photons emitted from the electromagnetic fields of relativistic heavy ions can fluctuate into quark anti-quark pairs and scatter from a target nucleus, emerging as vector mesons. These coherent interactions are identifiable by final states consisting of the two nuclei and a vector meson with a small transverse momentum. The emitters and targets can switch roles, and the two possibilities are indistinguishable, so interference may occur. Vector mesons are negative parity so the amplitudes have opposite signs. When the meson transverse wavelength is larger than the impact parameter, the interference is large and destructive. The short-lived vector mesons decay before amplitudes from the two sources can overlap, and so cannot interfere directly. However, the decay products are emitted in an entangled state, and the interference depends on observing the complete final state. The non-local wave function is an example of the Einstein-Podolsky-Rosen paradox.Comment: 13 pages with 3 figures; submitted to Physical Review Letter

Events with Isolated Charged Leptons and Large Missing Transverse Momentum at HERA

Striking events with isolated charged leptons, large missing transverse momentum and large transverse momentum of the hadronic final state were observed at the electron proton collider HERA in a data sample corresponding to a luminosity of about 130 pb-1. The H1 collaboration observed 11 events with isolated electrons or muons and with transverse momentum above 25 GeV. Only 3.4+-0.6 events were expected from Standard Model (SM) processes. Six of these events have a transverse momentum of greater than 40 GeV, while 1.3+-0.3 events were expected. The ZEUS collaboration observed good agreement with the SM. However, ZEUS found two events with a similar event topology, but tau leptons instead of electrons or muons in the final state. Only 0.2+-0.05 events were expected from SM processes. For various hypotheses the compatibility of the experimental results was investigated with respect to the SM and with respect to possible explanations beyond the SM. Prospects for the high-luminosity HERA-II data taking period are given