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Understanding the Properties of Chemical Freeze-Out

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

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Understanding the Properties of Chemical Freeze-Out

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  1. 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

  2. Outline The QCD phase diagram Chemical freeze-out Results from statistical model fits Role of phase boundaries Deconfinement phase transition (low μB) Quarkyonic phase transition (high μB) System size dependence Freeze-out parameters vs. Npart Indications for long lived hadronic phase ? Current experimental situation Early decoupling Rare particles with low hadronic cross sections Measurements at low energies Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  3. The QCD Phase Diagram Broad experimental program Past: SPS (and AGS) Present: RHIC and SPS Future: FAIR and NICA What can be learned at low energies? New exotic phases? Quarkyonic matter Can phase boundaries be mapped by hadron yields ? RHIC SPS FAIR NICA Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  4. The QCD Phase DiagramExperimental Access 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 size Program of NA61@SPS H. Stöcker, E.L. Bratkovskaya, M. Bleicher, S. Soff, and X. Zhu, JPG31, S929 (2005) Y.B. Ivanov, V.N. Russkikh, V.D. Tonnev, PRC73, 044904 (2006) 3-fluid hydro Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  5. Chemical Freeze-Out Statistical Model Fits • 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 • Andronic et al. • Phys. Lett. B673, 142 (2009). Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  6. Chemical Freeze-OutEnergy Dependence L. Kumar, QM11 Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  7. Chemical Freeze-OutWhere does Equilibration Happen? 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? Experiment Any evidences for long lived hadron gas phase after? Systematic studies at low energies 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. Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  8. Chemical Freeze-OutContinuous Freeze-Out Dynamical decoupling Should happen over certain time span and temperature range Theoretical approaches Hydro + hadronic transport (e.g. UrQMD) Hydro + extended freeze-out condition System size dependence Interplay mean free path and system size ⇒ decrease of T with increasing size (?) Hadronic cross section Rare particles (e.g. Ω) with low cross section ⇒ earlier freeze-out H. Petersen et al., PRC78, 044901 (2008) Hydro- phase S. Bass and A. Dumitru, PRC61, 064909 (2000). J. Knoll, NPA821, 235 (2009) H. van Hecke, H. Sorge, N. Xu, PRL81, 5764 (1998). Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  9. Chemical Freeze-OutRole of Phase Boundaries Equilibration Driven by proximity of freeze-out to phase boundary Deconfinement transition at low μB How about high μB? Quarkyonic matter Provides 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 ... P. Braun-Munzinger, J. Stachel, and C. Wetterich, PLB596, 61 (2004). A. Andronic et al., Nucl. Phys. A837, 65 (2010). L. McLarren and R.D. Pisarski, Nucl. Phys. A796, 83 (2007). S. Floerchinger and C. Wetterich arXiv:1202.1671 Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  10. System Size DependenceKinetic Freeze-Out Tkin decreases with increasing system size Dynamical decoupling: interplay mean free path and size of system Hydro reproduces trend Freeze-out condition: STAR: PRC83, 034910 (2011) U. Heinz and G. Kestin, PoS(CPOD2006), 038 Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  11. System Size Dependence Chemical Freeze-Out at small μB Different behaviour of Tkin and Tch Tkin: clear centrality dependence Tch: no centrality dependence Difficult to reconcile with hydro for normal HG Requires scattering rate proportional to Tn with n ≥ 20 At phase boundary: τΩ ∝ T-60 STAR: PRC83, 034910 (2011) U. Heinz and G. Kestin, PoS(CPOD2006), 038 P. Braun-Munzinger, J. Stachel, and C. Wetterich, PLB596, 61 (2004). Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  12. System Size Dependence Chemical Freeze-Out at higher μB (SPS) Tch changes with system size Central events of different A μB independent on system size Different freeze-out behaviour at different energies ? Careful systematic study needed Geometric effects (“core-corona”) might be important F. Becattini et al., PRC73, 044905 (2005) F. Becattini et al., PRC73, 044905 (2006), EPJC66, 377 (2010). Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  13. System Size Dependence Geometrical Effects (“Core-Corona”) • Corona: • Elementary N+N collisions • Core: • Dense fireball • System size dependencies determined by ratio core/corona • f (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 158A GeV C.B. J.Phys.Conf.Ser. 230, 012003 (2010) Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  14. System Size Dependence Chemical Freeze-Out at higher μB (RHIC) Recent STAR data Beam Energy Scan program Also significant system size dependence observed BUT: Tchincreases with system size! Opposite trend than observed by NA49 Contrary to naive expectation ? ⟶ Contribution by D. Blaschke pp data? L. Kumar, CPOD11 Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  15. Early Decoupling Rare Particles Particles with low hadronic cross section E.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 SPS More precise data on multi-strange particles (low energies) will be helpful • Andronic et al. • Phys. Lett. B673, 142 (2009). -/  = 1.5 (+ + -) NA49: PRL94, 192301 (2005). Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  16. Early DecouplingStrange Baryon to Pion Ratios _ Λ/π Λ/π X. Zhu, SQM11 Ξ-/π _ Ξ+/π Good agreement between SPS and RHIC Close to statistical model curve Low energy data scarce ⟶ FAIR and NICA Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  17. Early Decoupling Statistical Model Fits at Low √sNN HADES data: Ar+KCl at √sNN = 2.61 GeV Good agreement with statistical model fit Except: Ξ-! Off by factor 25 Sub-threshold production Also deviations for η (TAPS) Freeze-out parameter fit into known systematics How about system size dependence? M. Lorenz, CPOD11 Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  18. Early Decoupling Hydro + Cascade Predictions No real effect for Ωs No effect expected if Ω enters hadronic phase with equilibrium yield Strong effect on antibaryons Cascade removes p, Ξ+ ⇒ Reduction from chemical equilibrium Caveat: multi-meson fusion processes not included First implementation in transport: HSD (anti-protons) S. Bass and A. Dumitru, PRC61, 064909 (2000). _ _ R. Rapp and E. Shuyak, PRL86, 2980 (2001). Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  19. Early Decoupling Antibaryons Effect on statistical model fits Fits with and w/o antibaryons Studies ongoing System size dependence of p Tends to decrease towards central Indication for absorption in hadronic phase or just evolution of baryon number transfer ? Right now inconclusive High precision data required R. Stock et al., arXiv:0911.5705 NA49: PRC83, 014901 (2011) _ STAR: PRC83, 034910 (2011) Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  20. Early Decoupling Antibaryons 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 yet High precision data needed H. Petersen et al., PRC78, 044901 (2008) R. Stock et al., arXiv:0911.5705 Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  21. Early Decoupling Particle Ratios at LHC _ p/π- and K-/π- ratios p/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 M. Floris, QM11 K-/π- M. Floris, QM11 _ Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  22. Conclusions Freeze-out properties at low energies Indications 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 parameter No modification of rare particle yields (Ω, antiprotons) Experimental situation unclear No 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 ! Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  23. Backup Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  24. Chemical Freeze-Out System Size Dependence: Data LHC ALICE: Pb—Pb at √sNN = 2.76 TeV RHIC STAR: beam energy scan SPS NA61, NA49 K-/π- _ p/π- M. Floris, QM11 L. Kumar, QM11 Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  25. X. Zhu, SQM11 Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  26. IntroductionThe QCD Phase Diagram 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) Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  27. Kinetic Freeze-OutEarly Decoupling Particles with low hadronic cross section E.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 LHC Higher Tkin and lower 〈βT〉 for Ξ and Ω than for lighter hadrons (π, K, p) STAR: PRL92, 182301 (2004). N. Xu and M. Kaneta, NPA698, 306 (2002). NA49: PRL94, 192301 (2005). (A) Tkin = 90 MeV 〈βT〉 = 0.5 (B) Tkin = 170 MeV 〈βT〉 = 0.2 Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  28. − − / +/ Energy Dependence/π- and /π-Ratios / • NA49 data • Phys. Rev. C78, • 034918 (2008) • Transport models • OK for  • Too low for  • Statistical models • Generally good • description at all • energies |y| < 0.4 -/  = 1.5 (+ + -) |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 communication HSD: E. Bratkovskaya et al., Phys. Rev. C69, 054907 (2004) Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  29. Energy Dependenceϕ Meson: Total Yields At SPS yields not fully described by models UrQMD1.3 underestimates ϕ/π-ratio but good description of ϕ yield at lower energies Statistical model (γs = 1) above ϕ/π-ratio HGM: P. Braun-Munzinger et al., Nucl. Phys. A 687, 902 (2002). NA49 data Phys. Rev. C78, 044907 (2008) Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  30. Chemical Freeze-OutLimit μB → 0 and LHC Expectation Freeze-out points coincide with phase boundary at RHIC and top SPS energies Chiral phase transition from LQCD O. Kaczmarek et al., PRD83, 014504 (2011) P. Braun-Munzinger and J. Stachel, arXiv:1101.3167 Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  31. Chemical Freeze-Out Energy Dependence of Freeze-Out Parameters Parameterizations of Tch and μB as function of √sNN Freeze-out curve J. Cleymans et al., PRC73, 034905 (2006) • Andronic et al. • Phys. Lett. B673, • 142 (2009). Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

  32. Christoph Blume NICA/JINR-FAIR Workshop, FIAS Frankfurt

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