PowerPoint-Pr

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Energy dependence of hyperon production in PbPb
collisions at the CERN-SPS

Agnes Richard for NA49
Hot Quarks 2004
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• Introduction - motivation
• - overview of strangeness carriers
• Analysis - datasets, decay topologies
• - invariant mass
  spectra
• Results - mt and rapidity spectra
• Discussion - energy dependence
• - comparison to models
• Summary

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Introduction
observation in the energy dependence of
strangeness production maximum in K / p ratio
around 30 AGeV
PbPb (AuAu)
pp

• how do the hyperons behave?

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Indtroduction
strangeness carriers
strangeness conservation
s
s K (u s) ? K0 (d s)
K- (s u) ? K0 (s d)

isospin symmetry
?
ltlt
KAONS sensitive to total strangeness

? (u d s) ltlt ? (u
d s)
?- (d s s)
?- (d s s)
O (s s s)
O (s s s)

lt
lt
high baryon density
lt
lt
ANTIKAONS AND (ANTI)-HYPERONS sensitive to
total strangeness AND baryon density
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published ? Phys. Rev. Lett. 93, 022302
(2004) ? hep-ex/0202037,
Phys.Lett.B538 (2002) 275 preliminary ?
J.Phys. G30 (2004) S175 S180 ? J.Phys.
G30 (2004) S357 S362 to be expected soon
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decay topologies
p
? ? p p - BR 63.9 m 1.11568 GeV/c2 ct
7.89 cm
p -
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20 AGeV 30 AGeV 40
AGeV 40 AGeV
?
?
?
?
?
?
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• the raw data are corrected for
• reconstruction efficiency
• geometrical acceptance
• branching ratio
• based on
• Monte Carlo simulations
• embedding of the simulated signals in raw data
  events
• feeddown for the ? from?? decays
• the correction is calculated for 20 30 AGeV,
  for 40, 80 158 AGeV estimated as 6 for ? and
  12 for ? )

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158 AGeV
40 AGeV
? x 2 ? x0.3 ? ? x0.3

? x0.2 ? x0.2 ? x0.1
? ?
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?
?
158 AGeV 80 AGeV 40 AGeV 30 AGeV 20
AGeV
mt m0(GeV)
mt m0(GeV)
exponential fit
in the mt m0 range 0.4 1.4 GeV/c2
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(extracted from mt-spectra in the range 0.4 1.4
GeV/c2)
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40 AGeV 158
AGeV
? ? (x 5) ? ? (x 15)
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20 AGeV 30 AGeV 40 AGeV
80 AGeV 158 AGeV
 
lt ? gt 28 1.5 41.9 3.2 45.6 1.9
47.4 2.8 44.1 3.2 ? 0.76
0.02 0.99 0.04 1.16 0.06 -
- (statistical errors only)
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30 AGeV 40 AGeV 80 AGeV
158 AGeV
lt ? gt 0.32 0.07 0.74 0.04
2.26 0.25 3.87 0.18 ? 0.69
0.08 0.71 0.05 0.85 0.13
0.95 0.05 (statistical error only)
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AGS SPS RHIC
preliminary
lt? gt 1.5 ( lt?gt lt?-gt )
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• location of the anomalies in the ratio of strange
  to non-strange particles (?)
• maximum in lt ? gt / lt ? gt at around 30 AGeV
  ( 7.62 )
• and
• lt K gt / lt ? gt around 30 AGeV
• kink in
• lt K- gt / lt ?- gt around 30 AGeV
• ?not reproduced by hadron gas model!
• ref. Cleymans Redlich, Phys.Rev.C60054908,
  1999 nucl-th/9903063

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Energy dependence of hyperon to pion ratio
AGS SPS
? ? (x 7) ? ? (x 20)
lt? gt 1.5 ( lt?gt lt?-gt )
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hadron gas (g 1) Braun-Munzinger et
al., Nucl.Phys. A697902-912 hadron gas (g
free) Becattini et al., Phys.Rev.C69024905,
2004 UrQMD 1.3. Bleicher private communication
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• rich data on hyperons (L, X, W) in central PbPb
  collisions available in NA49
• L at 20 and 30 AGeV presented for the first time
• maximum in the L / p ratio is observed
• around 30 GeV
• appears at the same point as the anomalies in K/
  p and K-/ p- ratios

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EXTRA SLIDES
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?
?
?
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• ? impact parameter in the target plane
• z vertex of the ? decay

x
y
?
z
Target position
?-
p
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ln (p)