Slide 1

Elena Bratkovskaya FIAS, J.W. Goethe Universitt Frankfurt am Main Frankfurt am Main 01.04.2005, Bergen Energy and system size dependence in string-hadronic models Slide 2 Little Bangs in the Laboratory time Initial StateHadronization Au Quark-Gluon-Plasma ? quarks and gluons hadron degrees of freedom hadron degrees of freedom How can we proove that an equilibrium QGP has been created in central Au+Au collisions ?! Slide 3 The QGP in Lattice QCD T c = 170 MeV Lattice QCD: energy density versus temperature energy density versus temperature Quantum Cromo Dynamics (fundamental theory of quark-gluon interactions ): predicts strong increase of the energy density at critical temperature T C ~170 MeV Possible phase transition from hadronic to partonic matter (quarks, gluons) at critical energy density C ~1 GeV/fm 3 Critical conditions - C ~1 GeV/fm 3, T C ~170 MeV - can be reached in heavy-ion experiments at bombarding energies > 5 GeV/A Slide 4 The phase diagram of QCD UrQMD initial energy density is higher than the boundary from LQCD UrQMD initial energy density is higher than the boundary from LQCD Tri-critical point reached somewhere between 20 and 30 A GeV Tri-critical point reached somewhere between 20 and 30 A GeV -> we are probing a new phase of matter already at AGS! -> we are probing a new phase of matter already at AGS! Slide 5 Quark condensate in central Au+Au Quark condensate drops to zero already at lower AGS energies! Quark condensate drops to zero already at lower AGS energies! -> we are probing a new phase of matter already at AGS! -> we are probing a new phase of matter already at AGS! HSD calculations: NPA 674 (2000) 249 Slide 6 Strangeness enhancement Strangeness enhancement Charm suppression Charm suppression Collective flow (v 1, v 2 ) Collective flow (v 1, v 2 ) further signals of QGP: further signals of QGP: (not covered in this talk) (not covered in this talk) Multi-strange particle enhancement in Au+Au Jet quenching and angular correlations High p T suppression of hadrons Nonstatistical event by event correlations... Signals of QGP Signals of QGP Slide 7 HSD Hadron-String-Dynamics transport approach HSD Hadron-String-Dynamics transport approach UrQMD Ultra-relativistic-Quantum-Molecular-Dynamics UrQMD Ultra-relativistic-Quantum-Molecular-Dynamics Solution of the transport equations with collision terms describing: Solution of the transport equations with collision terms describing: elastic and inelastic hadronic reactions: baryon-baryon, meson-baryon, meson-meson baryon-baryon, meson-baryon, meson-meson formation and decay of baryonic and mesonic resonances string formation and decay Implementation of detailed balance on the level of 1 2 Implementation of detailed balance on the level of 1 2 and 2 2 reactions (+ 2 n multi-meson fusion reactions in HSD) and 2 2 reactions (+ 2 n multi-meson fusion reactions in HSD) Degrees of freedom: Degrees of freedom: baryons + mesons including excited states baryons + mesons including excited states strings; q, qbar, (qq), (qbar qbar) (no gluons!) strings; q, qbar, (qq), (qbar qbar) (no gluons!) Concepts: HSD & UrQMD Slide 8 very good description of particle production in pp, pA reactions very good description of particle production in pp, pA reactions unique description of nuclear dynamics from low (~100 MeV) to ultrarelativistic (21.3 TeV) energies unique description of nuclear dynamics from low (~100 MeV) to ultrarelativistic (21.3 TeV) energies HSD & UrQMD microscopic models for heavy-ion reactions HSD 1999 predictions Slide 9 Excitation function of +, K +, ( + 0 ) yields Reasonable description of strangeness by HSD and UrQMD Reasonable description of strangeness by HSD and UrQMD HSD overestimates pions at low AGS HSD overestimates pions at low AGS UrQMD overestimates pions at top AGS and above UrQMD overestimates pions at top AGS and above (deviations < 20%) (deviations < 20%) PRC 69 (2004) 015202 Slide 10 Excitation function of K + / +, K - / -, ( + 0 )/ ratios Experimental K + / + ratio shows a peak at ~30 A GeV -,horn- Experimental K + / + ratio shows a peak at ~30 A GeV -,horn- which is not reproduced by the transport approaches HSD and UrQMD ! which is not reproduced by the transport approaches HSD and UrQMD ! PRC 69 (2004) 015202 Slide 11 Transverse mass spectra - barometer of the reaction HSD & UrQMD 2.0: Transverse mass spectra of +, K + from p+p and p+A collisions are well reproduced at all energies Exp. data for light systems C+C and Si+Si at 160 A GeV are reasonably described by HSD and UrQMD m T =(m 2 +p T 2 ) 1/2 transverse mass T - inverse slope parameter PRL 92 (2004) 032302 Slide 12 m T spectra for Au+Au from AGS to RHIC HSD 2.0 & UrQMD 2.0: Pion slopes are only slightly underestimated by transport Kaon slopes are too low above 5 A GeV! PRC 69 (2004) 015202 Slide 13 Alternative scenarios (HSD) Hadronic medium effects Hadronic medium effects should happen: but practically dont enhance high m T -spectra (~10%) should happen: but practically dont enhance high m T -spectra (~10%) String-string interaction > overlapping strings String-string interaction > overlapping strings small effect on m T -slope with transverse string radius R s ~0.25fm small effect on m T -slope with transverse string radius R s ~0.25fm (depends on R s ) (depends on R s ) Isotropic decay of meson-baryon strings Isotropic decay of meson-baryon strings inconsistent with other observables (stopping and larger meson production) inconsistent with other observables (stopping and larger meson production) Nonleading parton (quark/diquark) elastic scattering with el( qq) = el N /N Quark Nonleading parton (quark/diquark) elastic scattering with el( qq) = el N /N Quark low effect at AGS, strong at RHIC, but hadron multiplicities low effect at AGS, strong at RHIC, but hadron multiplicities become too high become too high Reduced formation time F ->0 : too large hadron multiplicities Reduced formation time F ->0 : too large hadron multiplicities...... In all cases the improvement on the m T slope is small or inconsistent with other observables! PRC 69 (2004) 015202 Slide 14 Alternative scenarios: High mass baryon resonances - UrQMD 2.1 UrQMD 2.1 - model in spirit of RQMD: mB strings of invariant mass 2 < M < 3 GeV are replaced by quasi- particles (= high mass resonances) that decay isotropically according to the Br of the heaviest implemented resonance with the same quantum numbers mB strings of invariant mass 2 < M < 3 GeV are replaced by quasi- particles (= high mass resonances) that decay isotropically according to the Br of the heaviest implemented resonance with the same quantum numbers light meson ( ,K) emission is suppressed by ~ 25% compared to a string of the same invariant mass light meson ( ,K) emission is suppressed by ~ 25% compared to a string of the same invariant mass Isotropic mB elastic scattering instead of forward peaked leading hadron scattering Isotropic mB elastic scattering instead of forward peaked leading hadron scattering Strangeness suppression factor S has been enhanced from S =0.3 (UrQMD 1.3 or 2.0) to 0.5 (UrQMD 2.1) more strangeness production ! Strangeness suppression factor S has been enhanced from S =0.3 (UrQMD 1.3 or 2.0) to 0.5 (UrQMD 2.1) more strangeness production ! Improves T-slope, however, is inconsistent with other observables! PRC 69 (2004) 015202 Slide 15 Cronin effect at RHIC (HSD) Cronin effect: initial state semi-hard gluon radiation increases p T spectra already in p+A or d+A W. Cassing, K. Gallmeister and C. Greiner, Nucl. Phys. A 735 (2004) 277 Modelling of the Cronin effect in HSD: AA = PP (1+a N Prev ) AA = PP (1+a N Prev ) N Prev = number of previous collisions parameter a = 0.25 0.4 HSD without Cronin eff. HSD with Cronin eff. Slide 16 Cronin effect on , K + m T -spectra in A+A (HSD) Very small effect at AGSVery small effect at AGS Hardening of the m T spectra at top SPSHardening of the m T spectra at top SPS Substantial hardening of the m T spectra at RHIC > large improvement !Substantial hardening of the m T spectra at RHIC > large improvement ! Consistent with other observables !Consistent with other observables ! PRC 69 (2004) 015202 Slide 17 In UrQMD and HSD hadronic rescattering has only a small impact on the kaon slope In UrQMD and HSD hadronic rescattering has only a small impact on the kaon slope Cronin effect - initial state semi-hard gluon radiation- leads to the substantial hardening of the m T spectra at RHIC, however, has a very small effect at low energiesCronin effect - initial state semi-hard gluon radiation- leads to the substantial hardening of the m T spectra at RHIC, however, has a very small effect at low energies || || The hadron-string picture fails? The hadron-string picture fails? New degrees of freedom (colored partons q C, g a ) are missing ?! New degrees of freedom (colored partons q C, g a ) are missing ?! Inverse slopes T for K + and K - PRL 92 (2004) 032302 PRC 69 (2004) 015202 Slide 18 Directed flow v 1 & elliptic flow v 2 v 2 = 7%, v 1 =0 v 2 = 7%, v 1 =-7% v 2 = -7%, v 1 =0 Out-of-plane In-plane Y X - directed flow - elliptic flow V 2 > 0 indicates in-plane emission of particles V 2 < 0 corresponds to a squeeze-out perpendicular to the reaction plane (out-of-plane emission) x z Non central Au+Au collisions : interaction between constituents leads to a pressure gradient => spatial asymmetry is converted to an asymmetry in momentum space => collective flow Y Slide 19 Directed flow v 1 & elliptic flow v 2 for Pb+Pb at 40 A GeV Small wiggle in v 1 at midrapidity not described by HSD and UrQMD Small wiggle in v 1 at midrapidity not described by HSD and UrQMD Too large elliptic flow v 2 at midrapidity from HSD Too large elliptic flow v 2 at midrapidity from HSD and UrQMD for all centralities ! Experimentally: breakdown of v 2 at midrapidity ! Signature for a first order phase transition ! H. Stcker, NPA 750 (2005) E.B. et al., JPG 31 (2005) Slide 20 Directed flow v 1 for Au+Au at RHIC v 1 is flat at midrapidity for protons, pions and kaons v 1 is flat at midrapidity for protons, pions and kaons HSD shows slightly larger flow than UrQMD HSD shows slightly larger flow than UrQMD JPG 31 (2005) Slide 21 Elliptic flow v 2 in Au+Au at RHIC HSD, p T >2 GeV/c huge plasma pressure?! STAR data on v 2 of high p T charged hadrons are NOT reproduced in the hadron-string picture => STAR data on v 2 of high p T charged hadrons are NOT reproduced in the hadron-string picture => evidence for huge plasma pressure ?! PHOBOS data on v 2 for charged hadrons (all p T ) are underestimated in HSD by ~30% PHOBOS data on v 2 for charged hadrons (all p T ) are underestimated in HSD by ~30% W. Cassing, K. Gallmeister and C. Greiner, Nucl. Phys. A 735 (2004) 277 PRC 67 (2003) 054905 Slide 22 Charmonium in heavy-ion collisions Charmonium production versus absorption Obviously: there should be normal nuclear absorption, i.e. dissociation of charmonium by inelastic interactions with nucleons of the target/projectile Charmonium-N dissociation cross section can be fixed from p+A data D Dbar J/ CCCC Slide 23 NA50 Collaboration: J/ suppression in Pb+Pb J/ normal absorption by nucleons (Glauber model) || Experimental finding: extra suppression in A+A collisions; increasing with centrality Slide 24 Scenarios for charmonium suppression in A+A QGP color screening QGP color screening [Matsui and Satz 86] but (!) but (!) Lattice QCD predicts (2004): J/ can exist up to ~2 T C ! + Regeneration of J/ in QGP at T C : [Braun-Munzinger, Thews, Ko et al. `01] J/ +g c+cbar+g J/ +g c+cbar+g Comover absorption Comover absorption [Gavin & Vogt, Capella et al.`97]: charmonium absorption by low energy inelastic scattering with comoving mesons (m= J/ +m D+Dbar +m D+Dbar C +m D+Dbar Meson absorption cross section strongly model dependent abs mesons ~1-10 mb Existing exp. data at SPS (by NA50 Collaboration) are also consistent with comover absorption models ! Slide 25 J/ suppression in S+U and Pb+Pb at SPS Models: Comover model in the transport approach HSD/UrQMD Comover model in the transport approach HSD/UrQMD Comover model in the Glauber approach: Comover model in the Glauber approach: (1) without transition to QGP: Charmonia suppression increases gradually with energy density Charmonia suppression increases gradually with energy density [Capella et al.] (2) with transition to QGP: Charmonia suppression sets in Charmonia suppression sets in abruptly at threshold energy abruptly at threshold energy densities, where C is melting, J/ is melting densities, where C is melting, J/ is melting [Blaizot et al.] Statistical coalescence model (SCM).] Statistical coalescence model (SCM) [Kostyuk et al.] PRC 69 (2004) 054903 Slide 26 suppression in S+U and Pb+Pb at SPS Matrix element for + mesons D+Dbar Set 1: |M J/ | 2 =|M C | 2 =|M | 2 =|M 0 | 2 Set 2: |M J/ | 2 =|M C | 2 =|M 0 | 2 |M | 2 = 1.5 |M 0 | 2 PRC 69 (2004) 054903 Slide 27 J/ suppression in Au+Au at RHIC Time dependence of the rate of J/ absorption by mesons and recreation by D+Dbar annihilation: At RHIC the recreation of J/ by D+Dbar annihilation is important ! New data with higher statistics are needed to clarify the nature of J/ suppression! N DD ~16 Slide 28 suppression in Au+Au at RHIC is strongly suppressed in HSD at midrapidity recreation by D+Dbar annihilation doesnt compensate the absorption by mesons ! Charm chemical equilibration is not fully achieved in transport calculations on the basis of hadronic interactions since the to J/ ratio still depends on the matrix element for coupling to mesons Charm chemical equilibration is not fully achieved in transport calculations on the basis of hadronic interactions since the to J/ ratio still depends on the matrix element for coupling to mesons This allows to distinguish the different scenarios of charmonia suppression ! This allows to distinguish the different scenarios of charmonia suppression ! PRC 69 (2004) 054903 Slide 29 HSD: v 1 of D+Dbar and J/ from Au+Au versus p T and y at RHIC D-mesons and J/ follow roughly the charged particle flow around midrapidity ! nucl-th/0409047; PRC (2005) Slide 30 HSD: v 2 of D+Dbar and J/ from Au+Au versus p T and y at RHIC HSD: D-mesons and J/ follow the charged particle flow small v 2 < 3% HSD: D-mesons and J/ follow the charged particle flow small v 2 < 3% STAR data show very large collective flow of D-mesons v 2 ~15%! STAR data show very large collective flow of D-mesons v 2 ~15%! => strong initial flow of => strong initial flow of non-hadronic nature! non-hadronic nature! Collective flow from hadronic interactions is too low at midrapidity ! nucl-th/0409047; PRC (2005) Slide 31 AMPT model: v 2 of D+Dbar from Au+Au versus p T at RHIC AMPT multi-phase transport model: AMPT multi-phase transport model: (B. Zhang, L.-W. Chen and C.-M. Ko) (B. Zhang, L.-W. Chen and C.-M. Ko) Minijet partons from hard proceses (ZPC- Zangs parton cascade) + strings from soft processes (HIJING) Parton (q, qbar) scattering cross sections (3-10 mb) Parton (q, qbar) scattering cross sections (3-10 mb) To describe the large electron elliptic flow observed in available experimental data requires a charm quark scattering cross section that is much larger than given by perturbative QCD [nucl-th/0502056] [nucl-th/0502056] QGPis NOT an ideal gas QGP is NOT an ideal gas as described by pQCD! Slide 32 Summary I Collective flow signals of QGP Collective flow signals of QGP HSD, p T >2 GeV/c huge plasma pressure! SPS: proton flow (NA49) SPS: proton flow (NA49) small wiggle in v 1 and breakdown of v 2 at small wiggle in v 1 and breakdown of v 2 at midrapidity are not described by HSD and midrapidity are not described by HSD and UrQMD UrQMD signature for a first order phase transition ?! RHIC: v 2 of charged hadrons at high p T (STAR) RHIC: v 2 of charged hadrons at high p T (STAR) STAR data on v 2 of high p T charged hadrons are NOT reproduced in the hadron-string picture => evidence for a huge plasma pressure ?! Slide 33 Strangeness signals of QGP: Strangeness signals of QGP: Summary II Charm signals of QGP: Charm signals of QGP: horn in K + / + step in slope T Exp. data are not reproduced in terms of hadron-string picture => evidence for nonhadronic degrees of freedom STAR experiment at RHIC observed very strong collective flow v 2 of charm D-mesons => evidence for strong nonhadronic interactions in the very early phase of the reaction Slide 34 Outlook The Quark-Gluon-Plasma is there! But what are the properties of this phase ?! Initial idea (1970 2003): QGP is a weakly interacting gas of colored but almost massless quarks and gluons State of the art 2005: QGP is a strongly interacting and almost ideal color liquid ! New phase diagram of QCD A. Peshier, W. Cassing, PRL (2005) Slide 35 Thanks to my coauthors Steffen Bass Marcus Bleicher Wolfgang Cassing Andrej Kostyuk Marco van Leeuwen Manuel Reiter Sven Soff Horst Stcker Henning Weber Nu Xu HSD, UrQMD - open codes: http://www.th.physik.uni-frankfurt.de/~brat/hsd.htmlhttp://www.th.physik.uni-frankfurt.de/~urqmd.html