M.Zavertyaev

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Presented by M.Zavertyaev (Mikhail.Zavertiaev_at_mpi-
hd.mpg.de) for the Hera-B collaboration.
Outline

• Hera-B experiment
• Data set
• Search for signals of
• 4. Preliminary physics results
• 5. Conclusion

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The HERA-B Experiment at DESY
Top view
Beam 920 GeV/c protons
Subdetectors used in the present study
Acceptance 15-160(v) resp. 250(h) mrad
and mostly at mid rapidity (xF -0.15 0.05)

• Silicon vertex detector (SVD)
• Tracker (OTR)
• RICH

High mass resolution spectrometer
Good particle identification
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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
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The V0 selection.
(GeV/c)
Signal per Target - C Ti W - 1 0.45
0.85
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The Cascade Hyperons Selection.
V0
Beam p
p(K)
?(O)
A
p
?z /?
Statistics
Signal per Target - C Ti W - 1 0.45 0.85
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RICH identification
Identification thresholds
p - p gt 5 GeV/c
K - p gt 10 GeV/c
p - p gt 20 GeV/c
Particle Likelihood cut
gt 0.35
gt 0.55
gt 0.95
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Statistics
Statistics
Wire sharing C Ti W
1. 0.4 1.4
Wire sharing C Ti W
1. 0.5 1.6
events/10MeV
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The V0 and Hyperons p2t spectra.
The spectra follow a simple exponential law up to
1. GeV/c
WA89
d s / dp2t 8 exp(-Bp2t)
and show a flat behavior at higher p2t.
B

• The average ltp2tgt increases
• with the increase of the mass.
• A thermal model predicts an
• opposite curvature resp. to the
• experimental curve.

WA89
- HERA-B preliminary
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The Differential p2t spectra of K, F.
ds /dp2t 8 (1p2t/p20)-ß
valid for the whole p2t range
ß decreases for K from
6 to 4.5 for
CTiW targets
stable for F 4.3
for all targets. The
errors on the numbers are
from 5 to 8.
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Observation of Cronin effect.
a
dspA /dp2t Aa dspp /dp2t
The spectra were fit at each bin by formula
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 F.
In literature up to now many measurements and
predictions for stable hadrons available.
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ratio at different vs.
?
/
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The particle ratios.
K
K0S
p
?
p
?-
O-
HERA-B
K
vs 41.6GeV
F
The particle ratios measured by the four RHIC
collaborations, the statistical model and the
HERA-B result (preliminary).
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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.