1. Strangeness Production in p+A Collisions at √s = 41.6 GeV
Presented by
M.Zavertyaev
for the Hera-B collaboration.
Outline:
Hera-B experiment
Data set
Search for signals of
4. Preliminary physics results
5. Conclusion

2. The HERA-B Experiment at DESY
Top view
Beam GeV/c protons
Subdetectors used in the present
study:
Acceptance – (v) resp. 250(h) mrad
and mostly at mid rapidity (xF – )
Silicon vertex detector (SVD)
Tracker (OTR)
RICH
High mass resolution spectrometer
Good particle identification

3. The Target and Statistics.
Feature : works in the beam halo
1 kHz data acquisition rate.
Advantage : different target materials may be used
Minimum bias trigger
0.1 interaction per bunch crossing
Carbon
Titanium
Tungsten
Events

4. The V0 selection. Λ 1687687 +/- 1520 K0S 362492 +/- 563 171604 +/- 439
(GeV/c) Λ
/- 1520
K0S / /
Statistics : V0 p -
Beam p A π
Δz /γ
Signal per Target - C : Ti : W - 1 : 0.45 : 0.85

5. The Cascade Hyperons Selection.
p(p) V0
Beam p
Ξ(Ω)
π(K) A π
Δz /γ
Statistics: Ξ- Ω- Ξ +
7692 ± 133
4541 ± 115
863 ± 52
972 ± 52 Ω +
Signal per Target - C :Ti : W - 1 : 0.45 : 0.85

6. RICH identification Identification thresholds: π - p > 5 GeV/c
K p > 10 GeV/c
p p > 20 GeV/c
Particle Likelihood cut:
> 0.35
> 0.55
> 0.95

7. Statistics Statistics K+π- 534977 ± 3292 K-π+ 416720 ± 3083 K+K-
46629 ± 316
Wire sharing: C : Ti : W
1. : 0.4 : 1.4
Wire sharing: C : Ti : W
1. : 0.5 : 1.6
events/10MeV
mKπ
[GeV]

8. The V0 and Hyperons p2t spectra.
The spectra follow a simple
exponential law up to 1. GeV/c:
WA89
d σ / dp2t ∞ exp(-Bp2t)
and show a flat behavior at
higher p2t. B B
K0S
3.6 +/- 0.1 Ω +
0.93 +/- 0.4 Λ
2.4 +/- 0.1
2.2 +/- 0.1 Ξ-
1.8 +/- 0.2 Ξ
1.6 +/- 0.2 Ω-
0.95 +/- 0.4
The average <p2t> increases
with the increase of the mass.
A thermal model predicts an
opposite curvature resp. to the
experimental curve.
WA89
- HERA-B preliminary

9. The Differential p2t spectra of K*, Φ.σ
p [GeV ] 2 T
dσ /dp2t ∞ (1+p2t/p20)-β
valid for the whole p2t range
β : decreases for K* from
6 to 4.5 for
C:Ti:W targets
stable for Φ :
for all targets.
The errors on the numbers are
from 5 to 8%.

10. Observation of Cronin effect.α
The spectra were fit at each bin by formula:
dσpA /dp2t = Aα dσpp /dp2t
The spectra are enhanced at high p2t may be due to multiple scattering inside the
nucleus may be …..
Observed by HERA-B for K* and Φ.
In literature up to now many measurements
and predictions for stable hadrons available.

11. Λ / Λ
ratio at different √s.

12. The particle ratios. The particle ratios measured by the four RHIC
K0S K± Λ π± Λ p Ξ- Ξ + Ω- Ω +
HERA-B K*
√s = 41.6GeV Φ
The particle ratios measured by the four RHIC
collaborations, the statistical model and
the HERA-B result (preliminary).

13. Conclusion
The signals of strange particles at negative xF were observed at HERA-B.
The p2t differential production cross sections follow the existing dependencies.
The A dependencies were studied.
The Cronin effect was observed for K* and .
The evaluated particle ratios in pA interactions look very similar to the AA ones.