A. Donnachie

Total cross sections

Abstract Regge theory provides a very simple and economical description of all total cross sections.

Elastic Scattering and Diffraction Dissociation

Abstract High-energy elastic and inelastic scattering at small t are discussed in terms of pomeron and (where relevant) double-pomeron exchange. The similarity between pomeron exchange and photon exchange allows an almost parameter-free description of various elastic process, a and diffraction dissociation, in good agreement with experiment.

Small x: two pomerons!

Abstract Regge theory provides a very simple and economical description of data for (i) the proton structure function with x Q 2 values, (ii) the charm structure function, and (iii) γ p→J/ψ p . The data are all in agreement with the assumption that there is a second pomeron, with intercept about 1.4 . They suggest also that the contribution from the soft pomeron is higher twist. This means that there is an urgent need to make perturbative evolution compatible with Regge theory at small and not-so-small x , and to reassess the magnitude of higher-twist contributions at quite small x .

Dynamics of elastic scattering

Abstract If the energy scale of the long-range interaction is determined by the string tension and not by the nucleon mass, our previous dynamical model for high-energy pp and p p scattering is in excellent agreement with the data, both from the CERN ISR and the CERN Collider. Thus the interpretation of these data does not require any novel dynamical mechanism.

Evidence from πp phase shift analysis for nine more possible nucleon resonances

Abstract From πp phase shift analyses at 59 energies, linked with partial wave dispersion relation fits, we suggest the probable existence of nine new nucleon resonances in the mass range 1680–2190 MeV, all with very small branching ratios to the elastic channel.

Photoproduction and electroproduction of pions (I) dispersion relation theory

Abstract The dispersion relation theory of photo- and electroproduction of pions is reviewed and extended, exploiting the parallel between the two. Analytic expressions are given for the Born terms of the individual electroproduction multipoles and for the important kernels in the integral equations for the photoproduction multipoles. A sum rule is derived for the latter, and a discussion given of the application of the theory to data analysis, the results of which will be presented in a subsequent paper.

Complete experiments in pseudoscalar photoproduction

Necessary and sufficient conditions are derived for three double polarisation measurements to complement cross section and single polarisation measurements in pseudoscalar meson photoproduction to enable amplitudes to be determined up to discrete ambiguities. Rules for choosing two further measurements to resolve the discrete ambiguities are given and practical applications of the rules to particular reactions are discussed.

Diffractive deep inelastic lepton scattering

Abstract We calculate the structure function for deep inelastic lepton scattering events in which the target proton emerges isolated in rapidly and has its momentum changed very little by the scattering. This measures “the structure function of the pomeron”. We find that such events make up a few per cent of the total inclusive cross section at small values of the Bjorken variable x, so that it should be possible to measure the structure function at HERA.

Hard diffraction: Production of high pT jets, W or Z, and Drell-Yan pairs

We have previously calculated the quark content of the pomeron. This determines the diffractive structure function of the proton, which may be measured in deep inelastic lepton scattering at HERA. We now apply it to two hard diffractive pp or pp reactions. In these reactions, one initial proton or antiproton has its momentum changed very little by the interaction, and emerges isolated in rapidity. Our predicted cross sections for hard diffractive high pT jet production at SPS collider energy are between one and two orders of magnitude smaller than previous estimates. At this energy the cross section rises very rapidly with energy even for only moderately high pT. At SSC energy, of the order of 1% of jet events will be diffractive, over a wide range of pT. For W and Z production, the fraction of events that are diffractive at this energy will be about 10%, and for continuum dilepton production such a fraction will be achieved when the energy ✓s is greater than about 30mll.

pp and pp elastic scattering

Abstract We present an analysis of pp and p p elastic scattering in terms of various exchanges. Three-gluon exchange dominates at large t , and single-pomeron exchange at small t . The dip seen in high-energy pp scattering is provided by the interference of both of these with double-pomeron exchange. We predict that this dip will not be found in high-energy p p scattering. The dip that is seen in low-energy p p scattering is the result of the additional presence of reggeon-pomeron exchange.