A Study of the Multihadronic Properties of Photon-Photon Interactions

Lumsdon, Simon J (1990) A Study of the Multihadronic Properties of Photon-Photon Interactions. PhD thesis, University of Glasgow.

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The analysis described in this thesis concerns the study of hadron production in photon-photon interactions. The data analysed were taken with the CELLO detector on the PETRA storage ring at the DESY physics institute in Hamburg during 1986. During this time the machine operated with a centre of mass energy of 35 GeV and the total recorded integrated luminosity amounted to 86 pb-1. The data studied was split into three Q2 (where the Q2 is the invariant mass of the virtual photon) regions in the range 0 < Q2 < 30 GeV2 consisting of untagged events (with two undetected scattered beam leptons assumed to have been contained in the beam-pipe producing two nearly real photons) and single tagged events (where one beam lepton remain undetected producing a nearly real photon and one detected scattered beam lepton producing a highly virtual photon). Two tagging regions were used. Forward tags were detected in lead-glass scintillators close to the beam axis (55 < theta < 80 mr) and endcap tags were detected in the lead-liquid argon endcaps (150 < theta < 360 mr). The events were required to have ≥ 4 charged tracks and constrained to the hadronic mass WVIS region 4 ≤ WVIS ≤ 9 GeV. This produced three data samples, 15610 untagged events with ~0.1 GeV2, 371 forward tagged events with ~1.0 GeV2 and 302 endcap tagged events with ~12.7 GeV2. The data was compared to an incoherent sum of the quark parton model (QPM) and a soft hadronic term described by a generalised vector dominance model (GVDM). It was found that this gives reasonable overall agreement with the data. The overall numbers of events and their Q2 dependence was found to be in good agreement with an incoherent sum of QPM and a soft hadronic model whose W, Q2 dependence was best modelled by the GVDM ansatz. A jet analysis of the data showed it to be dominated by a two-jet component which was well modelled by the QPM + GVDM term. An excess of events at medium and high jet pt's was observed in the low Q2 data. The inclusion of a phasespace component, or rescaling the QPM component provided a good description of this excess. The thrust of the high jet pt events was described neither by the inclusion of a phasespace term (which underestimates the thrust), nor by scaling the QPM term (which overestimates the thrust). However, a good description of the thrust of high jet pt events was provided by the addition of a multijet term to GVDM + QPM.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: High energy physics
Date of Award: 1990
Depositing User: Enlighten Team
Unique ID: glathesis:1990-78161
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:38
Last Modified: 30 Jan 2020 15:38
URI: https://theses.gla.ac.uk/id/eprint/78161

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