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Sketch of a competitive experiment on dense
nuclear matter in the (future) Nuclotron energy
range (2-5 AGeV)
Helmholtz Summer School 2006, Dubna, Student
Seminar Peter Senger, GSI
1. The physics case ? Nuclear equation of
state at high baryon densities ? Search for a
first order phase transition between
hadronic matter and quark matter 2.
Observables ? Yield, spectra and collective
flow of hadrons incl. (multi-) strange
particles ? Event-by-event fluctuations of
particle yields and mean transverse
momenta ? Excitation functions (1-5 AGeV),
system size and centrality
dependence 3. Estimation of feasibility ?
Particle production cross sections in heavy ion
collisions ? Reaction rates 4. Experimental
conditions and requirements ? Beam energy and
intensity ? Detectors (tracking, momentum
determination, particle identification) ?
Efficiencies, signal-to background
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Transport calculations energy densities
Baryon density in central cell (AuAu, b0 fm)
HSD mean field, hadrons resonances strings
QGSM Cascade, hadrons resonances strings
C. Fuchs, E. Bratkovskaya, W. Cassing
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Ch. Fuchs, Tübingen
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Trajectories from UrQMD
L. Bravina, M. Bleicher et al., PRC 1998
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The critical point
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Strangeness production in central PbPb
collisions
C. Blume et al., nucl-ex/0409008 (CERN NA49)
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Multistrange hyperons from pBe, pPb and PbPb
at 158 AGeV/c
Strangeness enhancement
F. Antinori et al, Nucl. Phys. A 661 (1999) 130c
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Thermal production of multistrange hyperons ?
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Production processes of multistrange hyperons
Production processes and thresholds pp ? K ?0 p
( Ep? 1.6 GeV ) pp ? KK-pp
(Ep ? 2.5 GeV) pp ? K K ?- p ( Ep ? 3.7
GeV ) pp ? KKK?- p ( Ep ? 7.0 GeV )
?0 (s d u) m 1116 MeV ?- (s s d) m 1321
MeV ?- (s s s) m 1672 MeV
pp ? ?0 ?0 pp ( Ep ? 7.1 GeV ) pp ? ? ?-
pp ( Ep ? 9.0 GeV ) pp ? ? ?- pp ( Ep
? 12.7 GeV )
In heavy ion collisions cooking of
multistrange hyperons ? Strangeness exchange
reactions 2) ?0 K- ? ?-?0
?0 K ? ??0 3) ?- K- ? ?- ?-
? K ? ? ?
Enhanced yield at high densities
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Hyperon properties
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Particle multiplicities for central AuAu
collisionsfrom UrQMD calculations
AuAu 5 AGeV central minimum bias
8.2
2 0.06 0.015
0.0002 0.00005
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Reaction rate R NB ? NT/F ?

• R reactions/sec
• NB beam particles/sec
• cross section barn 10-24cm2
• NT /F target atoms/cm2 NA ?d/A
• with Avogadros Number NA 6.021023
  mol-1,
• material density ? g/cm3,
• target thickness d cm
• atomic number A
• ? efficiency

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Determination of target thickness

• Reaction cross section
• ?R ? (2 R)2 4 ?(r0A1/3)2 with r01.2
  fm
• AuAu collisions
• A197 ? ?R 6.1 barn, 1 barn 10-24 cm2

Reaction probability for AuAu collisions R/NB
?R NT/F 6.1 b 6.021023?d/A
6.1 10-24 cm2 6.02102319.3 g/cm3d/197
1 target thickness d 0.027 cm
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Production cross sections for min. bias AuAu
collisions at 5 AGeV ?(?) M(?) x ?R 2 x
6.1 b 12.2 b ?(?) M(?) x ?R
0.015 x 6.1 b 0.09 b ?(O) M(O) x ?R
0.00005 x 6.1 b 0.0003 b
Particle production probabilities for min. bias
AuAu at 5 AGeV R(?)/NB ?(?)NA?d/A ?(?)
b1.610-3 210-2 R(?)/NB ?(?)NA?d/A
?(?) b1.610-3 1.410-4 R(O)/NB
?(O)NA?d/A ?(O) b1.610-3 4.810-7
R(?)/NB ?(?)NA?d/A? ?
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• Acceptances and Efficiencies
• ??? ??p ?Det ?Trigg ?DAQ ?analysis
• with
• ??? angular acceptance
• ??p momentum acceptance
• ?Det detector efficiencies
• ?Trigg trigger efficiencies
• ?DAQ deadtime correction of DAQ
• ?analysis efficiency of analysis
• (track finding, cuts for
  background suppression , ...)

Typical values ??? ? 0.5, ??p? 0.8, ?Det? 0.9,
?Trigg ? 0.9, ?DAQ ? 0.5, ?analysis ? 0.3,
? ? 0.05
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Typical particle detection probabilities in AuAu
at 5 AGeV R(?)/NB ?(?)NA?d/A?
210-20.05 110-3 R(?)/NB ?(?)NA?d/A?
1.410-40.05 710-6 R(O)/NB
?(O)NA?d/A? 4.810-70.05
2.410-8 Required particle yield for a
competitive physics analysis (differential
values like v2 as function of pT) 1 Mio
particles Required number of beam particles
(integrated luminosity) for ? NB x sec 106/
110-3 1109 for ? NB x sec 106/ 710-6
1.41011 for O NB x sec 106/ 2.410-8
4.21013 Required beam time for a Au-beam
intensity of NB 106/sec for ? t 1103 sec
17 min for ? t 1.4105 sec 1.6 d for O
t 4.2107 sec 500 d
These numbers refer to one collision system and
one beam energy only. Systematic studies
require excitation functions (several beam
energies) with different collision systems !

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Possible experiment layout
TOF wall measures Time-of-flight for mass
determination.
needed fast detectors
tracking chambers
Dipole magnet
Time-of-flight wall (RPC)
Silicon tracker
Tracking chambers are needed to match tracks in
Silicon detector to hits in TOF wall
Silicon tracker in magnetic dipole field measures
tracks (particle numbers) and curvature
(particle momentum).
6 m
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? - Hyperons at AGS AuAu 6 AGeV

• Threshold production of Xi measured
• Main detector TPC with PID capabilities
• Measured in 4 centrality bins
• 250 Xi measured
• Results consistent with UrQMD
• Neural network algorithm used for the bgd
  suppression

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Invariant mass distributions ?-

• Invariant mass resolution is improved with the
  dca cut
• s 1.7 MeV
• Signal yield 264

After impact parameter cut
Before cuts
After dca cut
All cuts
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Invariant mass distributions O-

• Invariant mass resolution is improved with the
  dca cut
• s 2.2 MeV
• Signal yield 486

After impact parameter cut
Before cuts
After dca cut
All cuts
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Results on O- without PID
Statistics 1.4 108 events
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Invariant mass distributions O- with perfect PID
After impact parameter cut
Before cuts
After dca cut
All cuts
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Results on O- with perfect PID
Statistics 1.4 108 events
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Conclusions

• Multistrange hyperon measurements seem feasible
  in AuAu collision at 5 AGeV
• Track reconstruction, momentum determination and
  particle identification is required
• Beam intensities of better than NB 106/sec are
  needed

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Hyperon detection with STS without p, K, p
identification
central AuAu collisions at 25 AGeV
? ?- ?-
(sss)
(uds)
(dss)
efficiency 15.8 6.7
7.7