The Q{sup 2} and Transverse Momentum Dependence of Jet Production in Photon-Photon Interactions

Thesis/Dissertation · Mon Nov 19 04:00:00 EST 1984

OSTI ID:22413655

Tylka, Allan Joseph

An experimental study of jet production in photon-photon interactions is presented. The study is based on events collected with the PLUTO detector at the e{sup +}e{sup -} storage ring PETRA. The data sample, which corresponds to an integrated luminosity of ∼40 pb{sup -1} taken at an e{sup +}e{sup -} center-of- mass energy of 34.6 GeV, consists of 1226 events in the so-called 'single-tagged' mode, in which only one of the scattered beam electrons is detected. The data sample extends over the kinematic ranges 0.1 < Q{sup 2} < 18.0. GeV , where Q{sup 2} is the squared invariant mass of the tagged virtual photon, and jet transverse momentum (p{sub T}) up to ∼5 GeV/c, where p{sub T} is measured with respect to the photon-photon collision axis in the center-of-mass frame of the observed hadrons. At all Q{sup 2} the data show a high p{sub T} tail characteristic of hard, point-like interactions, as exemplified by the fundamental reaction γγ → qq-bar. The jet production cross-section approaches the standard Quark Parton Model (QPM) expectation for fractionally-charged quarks of three colors from above as either Q{sup 2} or jet p{sub T} increases. At Q{sup 2} ≥ 10 GeV the observed cross-section is consistent with the standard QPM to within ∼20% statistical uncertainty at all values of p{sub T}. This result rules out the naive Han-Nambu integrally-charged quark model at a level of about five standard deviations. It is demonstrated that overall the data are consistent with the hypothesis of a two-jet final state. Moreover, the total jet production cross-section is shown to be well-described by an incoherent sum of the Generalized Vector Dominance Model (GVDM), for which the final state is hadronized as two oppositely-directed low p{sub T} jets, and the QPM, which accounts for final states consisting of two high p{sub T} jets. Some discrepancies between the data and the GVDM+QPM Ansatz are observed. At Q{sup 2} ≤ 1 GeV{sup 2} and 1.5 ≤ jet p{sub T} ≤ 4.0 GeV/c, the data lie systematically above the GVDM+QPM prediction. The thrust distribution of the excess events, however, looks less two-jet-like than expected for quark jets with standard Feynman-Field fragmentation. Several possible interpretations of this excess, including that of higher-order Quantum Chromodynamic (QCD) processes, are discussed. (author)

• Research Organization: Department of Physics and Astronomy, University of Maryland, College Park, Maryland 20742 (United States)
• OSTI ID: 22413655
• Report Number(s): DOE-ER--02504-420
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CENTER-OF-MASS SYSTEM
COLOR MODEL
CROSS SECTIONS
ELECTRON BEAMS
GEV RANGE
GLUON MODEL
HADRONS
JETS
PHOTON-PHOTON INTERACTIONS
QUANTUM CHROMODYNAMICS
STORAGE RINGS
TRANSVERSE MOMENTUM
VECTOR DOMINANCE MODEL