Statistical Model Predictions for p+p and Pb+Pb Collisions at LHC
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Transcript of Statistical Model Predictions for p+p and Pb+Pb Collisions at LHC
Statistical Model Predictions for p+p and Pb+Pb Collisions at LHC
Ingrid Kraus
Nikhef and TU Darmstadt
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 2
Outline
• Predictions for Pb+Pb collisions at LHC– Extrapolation of thermal parameters, predictions
– Experimental observables for T and μB determination
• From Pb+Pb to p+p: system size dependence– Model ansatz with correlated, equilibrated clusters
– Analysed data and results
• Predictions for p+p collisions at LHC– Driven by initial or final state?
• Summary
in Collaboration with H. Oeschler, K. Redlich, J. Cleymans, S. Wheaton
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 3
Hadron ratios in the grand canonical ensemble
• Grand canonical ensemble– large systems, large number of produced hadrons
– two parameters describe particle ratios in the hadronic final
state
A. Andronic, P. Braun-Munzinger, J. Stachel, Nucl. Phys. A772(2006) 167
T, V,
T, Vb, Nb
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 4
On the freeze-out curve:
TLHC ≈ TRHIC ≈ 170 MeV
T ≤ TC ≈ 170 MeV
μB from parametrised
freeze-out curve:
μB (√(sNN) = 5.5TeV) = 1 MeV
Phys. Rev. C 73 (2006) 034905
Grand canonical ensemble
for Pb+Pb predictions
Thermal Parameters in Pb+Pb
Phys. Rev. C 73(2006) 034905
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 5
Predictions for Pb+Pb
• Reliable for stable
particles
• Benchmark for
resonances
Errors:
T = 170 +/- 5 MeV
μB = 1 + 4 MeV
Phys. Rev. C 74 (2006) 034903
- 1
All calculations with THERMUS hep-ph/0407174
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 6
T and μB dependence I: h / h ratios
• Sensitive on μB
determine μB from p/p
• weakly dep. on T
_
_☺
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 7
T dependence: ratios with large m
☺
• Ratios with larger mass
differences are more
sensitive
T from and/or
K
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 8
T and μB dependence II: mixed ratios
• Controlled by masses
• Weakly dep. on μB and T
• K/
– not usable for T and B
determination
– good test of predictions
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 9
Canonical suppression
• Canonical ensemble– small systems / peripheral collisions,
low energies
– suppressed phase-space for particles
related to conserved charges
– Stronger suppression for multi-strange
hadrons
– Suppression depends on strangeness
content, not difference
)(
)(
0 xI
xInn Scanonicalgrandi
canonicali
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 10
Canonical suppression
• Canonical ensemble– small systems / peripheral collisions, low
energies
– suppressed phase-space for particles
related to conserved charges
– Stronger suppression for multi-strange
hadrons
– Suppression depends on strangeness
content, not difference
– Suppressed strangeness production
beyond canonical suppression
)(
)(
0 xI
xInn Scanonicalgrandi
canonicali
SPS √(sNN) = 17 AGeV
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 11
Modification of the model
• Statistical Model approach: T and μB
– Volume for yields → radius R used here
• Deviations: strangeness undersaturation factor S
– Fit parameter
• Alternative: small clusters (RC) in fireball (R): RC ≤ R
– Chemical equilibrium in subvolumes: canonical suppression
– RC free parameter
• Study – p+p, C+C, Si+Si, Pb+Pb / Au+Au collisions
– at SPS and RHIC energies
R
RC
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 12
System size and energy dep. of cluster size
• Small clusters in all systems
• Small system size dependence
• p+p– energy dependence?
• Pb+Pb / Au+Au– data consistent with saturated
strangeness production
p+p C+C Si+Si Pb/Au
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 13
System size and energy dep. of cluster size
• A+A: clusters smaller than fireball
• RC not well defined for RC ≥ 2 fm because suppression vanishes
RC
= R
Pb+PbAu+Au
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 14
System size and energy dep. of cluster size
• Particle ratios saturate at RC ≈ 2 - 3 fm
– no precise determination for weak strangeness suppression
Pb+PbAu+Au
RC
= R
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 15
Extrapolation to LHC: T - B – systematics
• Chemical decoupling conditions
extracted from SIS up to RHIC
feature common behavior
• Extrapolation to LHC energy
with parametrisation e.g.
Nucl. Phys. A 697 (2002) 902
Phys. Rev. C 73(2006) 034905
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 16
System size and energy dep. of T and B
p+p C+C Si+Si Pb/Au
• T, μB weakly dependent on system size
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 17
Extrapolation to LHC: cluster size
• what defines RC in
p+p?
• initial size of p+p
system relevant
– RC const
• final state of large
number of produced
hadrons relevant
– RC increases with
multiplicity
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 18
Prediction for p+p
• significant increase of
ratios at RC ≈ 1.5 fm
• RC will be determined
with ALICE data
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 19
Extraction of RC
• Sensitivity increases
with strangeness
difference
RC from ☺hep-ph 0808.0611
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 20
• For Pb+Pb ratio was
proposed as a measure
of T but …
• Sensitivity on canonical
suppression is much
stronger than on T
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 21
Summary
• Pb+Pb– predictions for particle ratios with
extrapolated parameters T, μB
– T, μB determination with p / p and
/ K or / ratios
_
• p+p– predictions difficult due to
unknown degree of canonical
suppression
– Cluster radius RC from data
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 22
Data and fits
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 23
Data and fits II
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 24
Tables from paper
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Resonance Contribution to p/p
• Ratio not affected by feeding– net baryon number is conserved
_
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Resonance Contribution to K and
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 27
Resonance Decays
• no resonance contribution
• – 50% from feed-down
– both exhibit same T dependence
• K decay exceeds thermal at LHC
• – thermal production ≈ constant
– resonance contribution dominant
• 75% of all from resonances
• p/pprimary ≈ p/pdecay
_ _
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 28
Sensitivity on T
• Thermal– K / and / have
same T dependence
– sensitivity increases
with mass difference
• Decay contribution– lighter particles are
stronger affected
– increasing feed-down
with increasing T
Relative variation of R per 1MeV change of T
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 29
More SPS and RHIC 200 GeV Data
Ingrid Kraus, Nikhef QGP workshop, Erice, Sept 18, 2008 30
Model setting with S
• S
– sensitive on data sample
– increase with size
– increase with energy