understanding the properties of chemical freeze-out
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Understanding the Properties of Chemical Freeze-Out. NICA/JINR-FAIR Workshop “Matter at highest baryon densities in the laboratory and in space” April 2 – 4, 2012 FIAS. Christoph Blume University of Frankfurt. Outline. The QCD phase diagram Chemical freeze-out - PowerPoint PPT PresentationTRANSCRIPT
Understanding the Properties of Chemical Freeze-Out
Christoph BlumeUniversity of Frankfurt
NICA/JINR-FAIR Workshop“Matter at highest baryon densities in the laboratory and in space”April 2 – 4, 2012FIAS
Outline
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt 2
The QCD phase diagram
Chemical freeze-out Results from statistical model fitsRole of phase boundariesDeconfinement phase transition (low μB)Quarkyonic phase transition (high μB)
System size dependenceFreeze-out parameters vs. Npart
Indications for long lived hadronic phase ?Current experimental situation
Early decouplingRare particles with low hadronic cross sectionsMeasurements at low energies
The QCD Phase Diagram
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Broad experimental programPast: SPS (and AGS)Present: RHIC and SPSFuture: FAIR and NICA
What can be learned at low energies?
New exotic phases?Quarkyonic matter
Can phase boundaries be mapped by hadron yields ?
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RHIC
SPSFAIR
NICA
The QCD Phase DiagramExperimental Access
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt 4
Control parameter: √sNN Allows to scan different regions of phase diagram
System freezes out at different positions along freeze-out curve
Trajectory might cross critical area
Variation of system sizeProgram ofNA61@SPS
H. Stöcker, E.L. Bratkovskaya, M. Bleicher, S. Soff, and X. Zhu, JPG31, S929 (2005)
3-fluid hydro
Y.B. Ivanov, V.N. Russkikh,V.D. Tonnev, PRC73, 044904 (2006)
Chemical Freeze-Out Statistical Model Fits
A. Andronic et al. Phys. Lett. B673, 142 (2009).
Assumption: Multiplicities are determined by statistical weights (chemical equilibrium)
Grand-canonical partition function:
Parameters:V, T, B, (s)
Allows in general excellent fits to measured multiplicities
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt 5
Chemical Freeze-OutEnergy Dependence
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt 6
L. Kumar, QM11
Chemical Freeze-OutWhere does Equilibration Happen?
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Dynamical equilibration?QGP phase at high energies
How about lower energies?Hadron gas phase sufficient?
Other mechanisms?Phase space dominance?
Hadronization always leads to statistical equilibrium?
ExperimentAny evidences for long lived hadron gas phase after?
Systematic studies at low energies
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U. Heinz, Nucl. Phys. A661, 140 (1999).R. Stock, Phys. Lett. B456, 277 (1999).M. Gazdzicki and M. Gorenstein, Acta Phys. Polon. B30, 2705 (1999). J. Hormuzdiar et al., Int. J. Mod. Phys. E12, 649 (2003).V. Koch, Nucl. Phys. A715, 108 (2003).F. Becattini, arXiv:0901.3643.
Dynamical decouplingShould happen over certain time span and temperature range
Theoretical approachesHydro + hadronic transport (e.g. UrQMD)
Hydro + extended freeze-out condition
System size dependenceInterplay mean free path and system size
⇒ decrease of T with increasing size (?)
Hadronic cross sectionRare particles (e.g. Ω) with low cross section earlier freeze-out⇒
Chemical Freeze-OutContinuous Freeze-Out
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
H. van Hecke, H. Sorge, N. Xu, PRL81, 5764 (1998).
J. Knoll, NPA821, 235 (2009)
S. Bass and A. Dumitru, PRC61, 064909 (2000).
H. Petersen et al., PRC78, 044901 (2008)
Hydro-phase
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Chemical Freeze-OutRole of Phase Boundaries
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
A. Andronic et al., Nucl. Phys. A837, 65 (2010).
EquilibrationDriven by proximity of freeze-out to phase boundary
Deconfinement transition at low μB
How about high μB?
Quarkyonic matterProvides another phase boundary
Would determine position of chemical freeze-out points for higher μB
Consequence: no need for an extended hadronic phase
But: conjecture might be wrong ...
L. McLarren and R.D. Pisarski,Nucl. Phys. A796, 83 (2007).
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P. Braun-Munzinger, J. Stachel, and C. Wetterich,PLB596, 61 (2004).
S. Floerchinger and C. WettericharXiv:1202.1671
System Size DependenceKinetic Freeze-Out
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Tkin decreases withincreasing system sizeDynamical decoupling: interplay mean free path and size of system
Hydro reproduces trendFreeze-out condition:
U. Heinz and G. Kestin, PoS(CPOD2006), 038
STAR: PRC83, 034910 (2011)
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System Size Dependence Chemical Freeze-Out at small μB
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Different behaviour of Tkin and Tch
Tkin: clear centrality dependenceTch: no centrality dependence
Difficult to reconcile with hydro for normal HGRequires scattering rate proportional to Tn with n ≥ 20
At phase boundary: τΩ ∝ T-60P. Braun-Munzinger, J. Stachel, and C. Wetterich,PLB596, 61 (2004).
U. Heinz and G. Kestin, PoS(CPOD2006), 038
STAR: PRC83, 034910 (2011)
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System Size Dependence Chemical Freeze-Out at higher μB (SPS)
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Tch changes with system sizeCentral events of different A
μB independent on system size
Different freeze-out behaviourat different energies ? Careful systematic study needed
Geometric effects (“core-corona”) might be important
F. Becattini et al.,PRC73, 044905 (2005)
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√sNN Tch(p+p) Tch(Au+Au/Pb+Pb)
17.3 GeV 181.5 MeV 157.5 MeV
200 GeV 170.1 MeV 168.5 MeV
F. Becattini et al., PRC73, 044905 (2006),EPJC66, 377 (2010).
System Size Dependence Geometrical Effects (“Core-Corona”)
Corona:Elementary N+N collisions
Core:Dense fireball
System size dependencies determined by ratio core/coronaf (NW) = fraction of nucleons that scatter more than once (Glauber model)
P. Bozek, Acta Phys. Polon. B36, 3071 (2005).F. Becattini and J. Manninen, J. Phys. G35, 104013 (2008)J. Aichelin and K. Werner, Phys. Rev. C79, 064907 (2009)
K. Werner
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
158A GeV
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C.B. J.Phys.Conf.Ser. 230, 012003 (2010)
System Size Dependence Chemical Freeze-Out at higher μB (RHIC)
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Recent STAR dataBeam Energy Scan program
Also significant system size dependence observed
BUT:Tch increases with system size!Opposite trend than observed by NA49
Contrary to naive expectation ? ⟶ Contribution by D. Blaschke
pp data?
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L. Kumar, CPOD11
Early Decoupling Rare Particles
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
A. Andronic et al. Phys. Lett. B673, 142 (2009).
-/
= 1.5 (+ + -)
NA49: PRL94, 192301 (2005).
Particles with low hadronic cross sectionE.g. multi-strange baryons (Ω)
Might decouple earlier if there was a long lived hadronic phase
Deviations from statistical model fits?
No evidence seen at RHIC and SPSMore precise data on multi-strange particles (low energies) will be helpful
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Early DecouplingStrange Baryon to Pion Ratios
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt 16
X. Zhu, SQM11
Good agreement between SPS and RHICClose to statistical model curve
Low energy data scarce FAIR and NICA⟶
Λ/π
Λ/π_
Ξ-/π
Ξ+/π_
Early Decoupling Statistical Model Fits at Low √sNN
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt 17
HADES data: Ar+KCl at √sNN = 2.61 GeVGood agreement with statistical model fit
Except: Ξ-! Off by factor 25Sub-threshold production
Also deviations for η (TAPS)
Freeze-out parameter fit into known systematics
How about system size dependence?
M. Lorenz, CPOD11
Early Decoupling Hydro + Cascade Predictions
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
No real effect for ΩsNo effect expected if Ω enters hadronic phase with equilibrium yield
Strong effect on antibaryonsCascade removes p, Ξ+
⇒ Reduction from chemical equilibrium
Caveat: multi-meson fusion processes not included
First implementation in transport: HSD(anti-protons)
_ _
R. Rapp and E. Shuyak, PRL86, 2980 (2001).
S. Bass and A. Dumitru,PRC61, 064909 (2000).
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Early Decoupling Antibaryons
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Effect on statistical model fitsFits with and w/o antibaryonsStudies ongoing
System size dependence of pTends to decrease towards central
Indication for absorption in hadronic phase or just evolution of baryon number transfer ?
Right now inconclusiveHigh precision data required
R. Stock et al., arXiv:0911.5705
STAR: PRC83, 034910 (2011)
NA49: PRC83, 014901 (2011)
_
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Early Decoupling Antibaryons
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Antibaryons removed by hadron gas phase ?Simulation with hydro model + hadronic afterburner (UrQMD)
Afterburner removes antibaryons (p, Λ, Ξ) Reduction from chemical ⇒equilibrium value
Caveat: multi-meson fusion processes not simulated
No final conclusion from data yetHigh precision data needed
R. Stock et al.,arXiv:0911.5705
H. Petersen et al., PRC78, 044901 (2008)
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Early Decoupling Particle Ratios at LHC
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
M. Floris, QM11
K-/π- M. Floris, QM11
p/π- and K-/π- ratiosp/π-(LHC) = K-/π-(BRAHMS+PHENIX) (STAR: not feed down corrected!)
K-/π-(LHC) = K-/π-(RHIC)
_p/π-_
_
Statistical model predictions
Note: fit to larger set of particles (π, K, p, Λ, Ξ, Ω) results in expected Tch, problem only with p, p
_
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Conclusions
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Freeze-out properties at low energiesIndications for presence of phase boundary to quarkyonic matter?
⟶ drives particle yields to equilibrium
If yes, no need for extended hadron gas phase
Indicators:No system size dependence of freeze-out parameterNo modification of rare particle yields (Ω, antiprotons)
Experimental situation unclearNo system size dependence at low μB
Results at high μB not in agreement (NA49, STAR)Data on rare particles scarce at low energies
Many opportunities for experiments at NICA and FAIR !
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Backup
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt 23
Chemical Freeze-Out System Size Dependence: Data
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
LHCALICE: Pb—Pb at √sNN = 2.76 TeV
RHICSTAR: beam energy scan
SPSNA61, NA49
L. Kumar, QM11
p/π-_ K-/π-
M. Floris, QM11
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Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt 25
X. Zhu, SQM11
IntroductionThe QCD Phase Diagram
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Variation of √sNN → Different regions of phase diagram
→ Map of chemical and kinetic freeze-out points
Limit μB → 0:RHIC experiments
New: ALICE (LHC)
High μB:SPS + AGS
New: STAR Beam Energy Scan (BES) NA61 (SPS)
Future: CBM (FAIR) + MPD (NICA)
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Kinetic Freeze-OutEarly Decoupling
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
STAR: PRL92, 182301 (2004).
Particles with low hadronic cross sectionE.g. multi-strange baryons (Ξ, Ω)
Should decouple earlier
Less affected by transverse expansion of hadronic phase
Effect visible in BW fits at RHIC and LHCHigher Tkin and lower 〈 βT 〉 for Ξ and Ω than for lighter hadrons (π, K, p)
NA49: PRL94, 192301 (2005).
(A) Tkin = 90 MeV 〈 βT 〉 = 0.5(B) Tkin = 170 MeV 〈 βT 〉 = 0.2
N. Xu and M. Kaneta, NPA698, 306 (2002).
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Energy Dependence/π- and /π-Ratios
NA49 dataPhys. Rev. C78, 034918 (2008) Transport models
OK for
Too low for Statistical models
Generally good description at allenergies
|y| < 0.4
|y| < 0.5
SHM(B): A. Andronic et al. Nucl. Phys. A 772, 167 (2006).UrQMD: M. Bleicher et al., J. Phys. G 25, 1856 (1999) and private communicationHSD: E. Bratkovskaya et al., Phys. Rev. C69, 054907 (2004)
/
/−
-/ +/− = 1.5 (+ + -)
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Energy Dependenceϕ Meson: Total Yields
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt 29
At SPS yields not fullydescribed by models
UrQMD1.3 underestimates ϕ/π-ratiobut good description of ϕ yieldat lower energies
Statistical model (γs = 1) above ϕ/π-ratioHGM: P. Braun-Munzinger et al., Nucl. Phys. A 687, 902 (2002).
NA49 dataPhys. Rev. C78, 044907 (2008)
Chemical Freeze-OutLimit μB → 0 and LHC Expectation
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
Freeze-out points coincide with phase boundary at RHIC and top SPS energiesChiral phase transition from LQCD
P. Braun-Munzinger and J. Stachel,arXiv:1101.3167
O. Kaczmarek et al., PRD83, 014504 (2011)
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Chemical Freeze-Out Energy Dependence of Freeze-Out Parameters
Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt
A. Andronic et al. Phys. Lett. B673, 142 (2009).
Parameterizations of Tch and μB as function of √sNN
Freeze-out curveJ. Cleymans et al., PRC73, 034905 (2006)
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