The Perturbative Evolution of the Photon Structure Function.
Abstract
Available from UMI in association with The British Library. Requires signed TDF. There has been recent interest in predicting the parton distributions of the photon through perturbative evolution using the AltarelliParisi evolution equations, but no real consistency in the region or scale of momentum transfer, Q^2, in which this perturbative technique is applied. In this thesis we show that one is unable to perturbatively evolve the input parton distributions of the photon and consistently reproduce the data for the structure function, F_2, at higher values of momentum transfer, starting from initial scales of Q^2 <=q 5 GeV^2 ~imately. Thus, we draw the conclusion that it is invalid to treat the photon perturbatively below this value of Q^2. Furthermore we demonstrate that the evolution of F^2 is sensitive to the value of Q.C.D. scale parameter Lambda_{overline{MS }} over large evolution ranges, typically 5 to 100 GeV^2, and that is this sensitivity is lost for smaller ranges, which agrees with the theoretical work of Frazer (1987). We also successfully include, using a physically motivated model, the higher order, nexttoleading order, corrections in an analysis that incorporates the characteristic pointlike component of F_2 at values of Q^2 greater than 5 GeV^2 and is independent of the quark masses. We demonstrate that the evolved F_2 is insensitive to the shape and normalisation of the gluon input and that one is unable to obtain any information about the gluon content of the photon using F_2 from a perturbative evolution. Finally, we show that the conclusions of Drees and Godbole (1988), regarding the sensitivity of the two jet crosssection at ep colliders to the photon parton content, still holds when one considers parton distributions of the photon that have been evolved in the perturbative region determined and quoted above. This leads us to conclude that it is unlikely that one can determine anything definitive about the gluon content of the photon using the evolution of F_2 or the high p_{T} jet crosssections at HERA.
 Publication:

Ph.D. Thesis
 Pub Date:
 1989
 Bibcode:
 1989PhDT.......175H
 Keywords:

 Physics: Elementary Particles and High Energy