Diffraction in electron-proton collisions

Subject of this thesis is diffractive collisions of electrons and protons, i.e. collisions wher~ the proton remains intact or is slightly excited, and loses only a small fraction of its initial energy. Such processes can be described by the exchange of a pomeron, which is well-known from the phenomenology of highenergy hadron scattering but far from being understood in the framework of quantum chromodynamics. We use the simple model of Landshoff and Nachtmann, where the pomeron is approximated by two nonperturbative gluons, to calculate the cross section for diffractive production of a quark-antiquark pair from a real or virtual photon. This allows us to give detailed predictions for diffractive electro- or photoproduction of a jet pair, for diffractive charm production, and for the inclusive cross section in diffractive deep inelastic scattering at not too large masses of the diffractive system. For the latter we find rather good agreement with the data taken at the HERA collider, taking into account the uncertainties of our calculation. We then turn our attention to azimuthal correlations in diffractive scattering. The dependence of the electron-proton cross section on the angle between the lepton plane and some direction in the hadronic final state has a simple relation with cross sections and interference terms of the photon-proton subprocess for definite photon helicity. Its measurement can be used to constrain the cross section for longitudinally polarised photons. We compute the distribution of the azimuthal jet angle in diffractive dijet production in the Landshoff-Nachtmann model and find that useful bounds on the longitudinal cross section for such events might be obtained from its measurement. Going further we extend our calculation of quark-antiquark production to finite squared momentum transfer from the proton. This enables us to investigate the distribution of another important azimuthal angle, that of the scattered proton, which contains information about the helicity of the pomeron. The last part of this thesis is devoted to the phenomenological pomeron model of Donnachie and Landshoff. When applied to diffractive quark-antiquark production it violates electromagnetic gauge invariance. We suggest a prescription to deal with this problem and compare the results we then obtain with those of the Landshoff-Nachtmann model. We find remarkable similarities between the two models, but they also show important differences, especially in details of kinematical distributions.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

1996

Author dc:creator

• Diehl, Markus

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/b815ebb7-282e-4fdc-920f-4caa0f069883/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.11660

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/265482