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Title: Strange particle production at the ZEUS detector
Author: Cottrell, Andrew C.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2005
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The production of the neutral strange particles Λ, Λ[bar] and K0s at HERA has been studied with the ZEUS detector, using an integrated luminosity of 121pb-1 . Differential cross-sections are measured in a High Q2 DIS sample (Q2 ≥ 25GeV2), a Low Q2 DIS sample (5 ≤ Q2 ≤ 25GeV2 ) and a photoproduction sample. The photoproduction sample has Q2 <= 1GeV2 and at least two jets that satisfy ETjet > 5GeV and |ηjet| < 2.4. Cross-sections are measured as a function of the particle PT and η, and additionally as a function of the event Q2 and x in the DIS samples, and as a function of xγ in the photoproduction sample. The DIS cross-sections are compared to the ARIADNE Monte Carlo, which broadly describes the data. The photoproduction cross-sections are compared to PYTHIA, where the agreement is less good, particularly at low xγ. The baryon-antibaryon asymmetry, defined as (Λ-Λ[bar])/(Λ+Λ[bar]), is measured and always found to be consistent with zero, indicating little transfer of the Baryon Number from the beam proton to the Λ system in the detector region. The polarization of Λ and Λ[bar] is measured and also found to be always consistent with zero, indicating that there is no preferred frame in Λ production. The baryon-meson ratio (Λ + Λ[bar])/K0s is studied, and is found to generally agree with ARIADNE in DIS, but give an excess over PYTHIA in photoproduction. The excess is particularly prominent at low xγ in events with no clear jet structure. This is interpreted as hadron production in this region depending on a more-than-one-dimensional overlap of quark wave functions. An excess of strangeness in this region at low xγ with no high ET jets would be significant. It is investigated by taking the ratio of strange particles to charged tracks but no excess is seen.
Supervisor: Walczak, Roman Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Particles (Nuclear physics) ; Strange particles ; Hadrons