The production of the neutral strange particles Λ, Λ[bar] and K<sup>0</sup><sub>s</sub> at HERA has been studied with the ZEUS detector, using an integrated luminosity of 121pb<sup>-1</sup> . Differential cross-sections are measured in a High Q<sup>2</sup> DIS sample (Q<sup>2</sup> ≥ 25GeV<sup>2</sup>), a Low Q<sup>2</sup> DIS sample (5 ≤ Q<sup>2</sup> ≤ 25GeV<sup>2</sup> ) and a photoproduction sample. The photoproduction sample has Q<sup>2</sup> <= 1GeV<sup>2</sup> and at least two jets that satisfy E<sub>T</sub><sup>jet</sup> > 5GeV and |η<sup>jet</sup>| < 2.4. Cross-sections are measured as a function of the particle P<sub>T</sub> and η, and additionally as a function of the event Q<sup>2</sup> and x in the DIS samples, and as a function of x<sub>γ</sub> 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 x<sub>γ</sub>. 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])/K<sup>0</sup><sub>s</sub> 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 x<sub>γ</sub> 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 x<sub>γ</sub> with no high E<sub>T</sub> jets would be significant. It is investigated by taking the ratio of strange particles to charged tracks but no excess is seen.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:434852 |
| Date | January 2005 |
| Creators | Cottrell, Andrew C. |
| Contributors | Walczak, Roman |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:2b53f255-4201-4ce4-98ca-13d6c0f49d5b |
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