K0S%20and%20L%20production%20at%20ZEUS

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K0S and L production at ZEUS

• Alexander A. Savin
• University of Wisconsin
• On Behalf of the ZEUS Collaboration
• DIS 2006, Tsukuba, Japan

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Outline

• Strange mesons and baryons cross sections
• Baryon-antibaryon asymmetry
• Baryon to meson ratio
• Strange to light mesons ratio
• Polarization.
• In the wide kinematic range of ep interaction
  at HERA

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Kinematic Variables
e(-)
p
(820)
Photon virtuality
inelasticity
Bjorken scaling variable
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Event and Particle Selection
ZEUS 1996-2000 data 121 pb-1
DIS 5ltQ2lt25 or Q2gt25 GeV2 0.02ltylt0.95
PHP Q2lt1 GeV2 0.2ltylt0.85 2 jets with
ETjetgt5 GeV
Particle selection - Secondary vertex
-
-
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Strange production mechanism
- strangeness suppression factor
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K0S DIS cross sections
ARIADNE with 0.3 describes data well, 0.2 less
satisfactory LEPTO does not describe the data
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L DIS cross sections
ARIADNE with 0.3 describes data well, 0.2 less
satisfactory LEPTO does not describe the data
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PHP cross sections
PYTHIA describes the data well, xgOBS is too flat
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Baryon-antibaryon asymmetry
- small or no asymmetry - gluon junction
mechanism, 3.5 positive, RHIC
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Baryon to meson ratio
Low Q2 region is better described by the ARIADNE
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Baryon to meson ratio
- ARIADNE reasonably describes the data - the
ratios are similar to those from ee and pp.
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Photoproduction with 2 jets
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Fireball type of event
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Fireball sample selection
Total transverse energy
Highest transverse energy jet
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Baryon to meson ratio, PHP
Similar to DIS
PYTHIA does not describe fireball enriched sample
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Strange to light hadrons ratio
Nch number of charged pions, charged kaons,
protons and antiprotons
Similar to ee
ARIADNE with 0.22 describes data well
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Strange to light hadrons ratio
PYTHIA describes data well (instanton
contribution?)
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Polarization
Polarization in scattering due to the strong
interaction

• 0.642 - decay asymmetry
• parameter

q - angle between the proton(antiproton)
direction and the polarization axis
No polarization
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Summary

• Measurements of K0S, Ls production have been
  made at ZEUS using 121 pb-1 int.luminosity
• no baryon-antibaryon asymmetry is observed
• no transverse polarization is observed
• ARIADNE and PYTHIA describe data well. For the
  strange to light meson ratio ARIADNE requires
  strangeness suppression factor 0.22, rather than
  0.3, which used to describe other distributions
• the ratio of baryons to mesons is large in the
  PHP resolved region and in the fireball PHP
  region, is much larger than in ee and is not
  described by PYTHIA