1. K0S and L production at ZEUS
Alexander A. Savin
University of Wisconsin
On Behalf of the ZEUS Collaboration
DIS 2006, Tsukuba, Japan

2. 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

3. Kinematic Variables e+(-) p Photon virtuality inelasticity
(820)
Photon virtuality
inelasticity
Bjorken scaling variable

4. Event and Particle Selection
ZEUS data 121 pb-1
DIS:
5<Q2<25 or Q2>25 GeV2;
0.02<y<0.95
PHP:
Q2<1 GeV2;
0.2<y<0.85
2 jets with ETjet>5 GeV
Particle selection: - Secondary vertex ; -

5. Strange production mechanism
- strangeness suppression factor

6. K0S DIS cross sections
ARIADNE with 0.3 describes data well, 0.2 less satisfactory
LEPTO does not describe the data

7. L DIS cross sections
ARIADNE with 0.3 describes data well, 0.2 less satisfactory
LEPTO does not describe the data

8. PHP cross sections
PYTHIA describes the data well, xgOBS is too flat

9. Baryon-antibaryon asymmetry
- small or no asymmetry ;
- “gluon junction mechanism”, 3.5% positive, RHIC

10. Baryon to meson ratio
Low Q2 region is better described by the ARIADNE

11. Baryon to meson ratio - ARIADNE reasonably describes the data;
- the ratios are similar to those from ee and pp.

12. Photoproduction with 2 jets

13. Fireball type of event

14. Fireball sample selection
Total transverse
energy
Highest
transverse
energy jet

15. Baryon to meson ratio, PHP
Similar to DIS
PYTHIA does not describe fireball enriched sample

16. 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

17. Strange to light hadrons ratio
PYTHIA describes data well (instanton contribution?)

18. Polarization No polarization Polarization in scattering due
to the strong interaction
= decay asymmetry
parameter
q - angle between the
proton(antiproton) direction
and the polarization axis
No polarization

19. Summary
Measurements of K0S, L’s 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