Can flavor hierarchy in the QCD phase transition change our understanding of hadronization ? R. Bellwied (University of Houston) in collaboration with S.Jena, M. McDonald, M.Weber (University of Houston) C. Ratti, M. Bluhm, W. Alberico (Torino University & INFN) S. Borsanyi & Z. Fodor (University of Wuppertal) S. Katz (Eotvos University, Budapest) 1
Outline • Experimental evidence of hadronization patterns • Non-equilibrium vs. equilibrium hadronization • The impact of formation time and quasi-particles • Recent input from lattice QCD • The role of flavor during the transition • Experimental evidence of flavor dependent hadronization patterns • New experimental / theoretical avenues 2
Any measure of hadron formation must rely on particle identified patterns. Easiest distinction: Baryons vs. mesons B/M ratio at intermediate transverse momentum shows baryon anomaly (baryons enhanced by a factor three relative to pp)
Nuclear suppression pattern in heavy ion collisions becomes more complex Surprising particle dependence in R AA (hadro-chemistry or flavor change) ? This is not simple partonic energy loss.
Two distinctly different hadronization processes (both postulated in 1977) More likely in vacuum ? (non-equilibrium) More likely in medium ? (equilibrium) 5
Non-equilibrium modeling of hadronization using light cone variables Inside-outside cascade (Lorentz boost) τ o ~ 1 fm/c : proper formation time in hadron rest frame E : energy of hadron m: mass of hadron E/m = γ high energy particles are produced later heavy mass particles are produced earlier C. Markert, RB, I. Vitev (PLB 669, 92 (2008)) Outside-inside Cascade (energy conseervation) large z (=ph / pq) short formation time
The formation time of hadrons (for parton fragmentation in medium) Can a hadron form inside the deconfined medium above T c ? Three Scenarios: A parton traverses A parton fragments A parton converts into a pre-hadronic the medium and inside the medium state or a quasi-particle which traverses the fragments outside medium and fragments outside. Color transparency of color neutral objects to colored medium. Is the energy loss in medium affected by the formation of the hadronic state ? Are the properties of the hadronic state affected by the formation in medium ? Signatures: any early probe which is sensitive to the medium (e.g. energy loss or v2) Explains R AA of baryons and mesons (m h difference = formation time difference).
The formation time of hadrons (for parton fragmentation in medium) Can a hadron form inside the deconfined medium above T c ? Three Scenarios: A parton traverses A parton fragments A parton converts into a pre-hadronic the medium and inside the medium state or a quasi-particle which traverses the fragments outside medium and fragments outside. Color transparency of color neutral objects to colored medium. Is the energy loss in medium affected by the formation of the hadronic state ? Are the properties of the hadronic state affected by the formation in medium ? Signatures: any early probe which is sensitive to the medium (e.g. energy loss or v2) Explains R AA of baryons and mesons (m h difference = formation time difference).
Quasi-particle or hadronic bound state - Is there a difference ? A quasi-particle is a colored object, i.e. a dressed up quark or glueball which has attained a thermal mass that can potentially exceed the final state hadron mass and then decay into the hadronic state. (e.g. Cassing & Bratkovskaya (DQPM model, PRC 78, 034919 (2008))) = Late Color Neutrality A hadronic bound state is a color neutral object that approaches the final hadronic wave function during its evolution, i.e. quark content fixed but not all hadron properties fixed (e.g. Kopeliovich or Accardi) = Early Color Neutrality A colored object will continue to interact and not develop a hadronic wave function early on (constituent quark or quasi-particle) A color-neutral object will have a reduced size and interaction cross section (color transparency) and develop wave function properties early Only a color neutral state can exhibit hadronic features (e.g. can pre- resonance decay prior to pion hadronization ?)
B/M ratio at intermediate transverse momentum shows baryon anomaly (baryons enhanced by a factor three relative to pp) baryon meson Recombination in medium Fragmentation in vacuum
Does this make sense near the QCD phase transition ? A re-interpretation of the Polyakov Loop calculation in lattice QCD Low energy collisions (AGS, SPS, RHIC scan, FAIR): survival of resonant states formation High energy collisions (RHIC, LHC): formation of pre-hadronic states survival RB et al., PLB691 (2010) 208 Data: Bazavov et al., arXiv:1105:1131
Lattice QCD predictions for QCD transition Recent high resolution lattice calculations have yielded reliable continuum extrapolations for all relevant order parameters of the QCD phase transition. Difference between light and strange flavor The conclusions are: A.) that the transition is an analytic crossover for an extended range of temperatures ( Δ T around 100 MeV) B.) that in the crossover region there might be indications of a flavor hierarchy during hadronization (heavier flavors freeze out at higher temperatures, more abundant if emission is statistical). C. Ratti et al., PRD 85, 014004 (2012) R. Bellwied, arXiv:1205.3625 12
Lattice QCD susceptibility predictions Overall a remarkable separation of transition behavior in the crossover region for different quantum numbers. (all calculations for zero chemical potential = comparable to LHC energies). S. Borsanyi et al., arXiv:1112.4416 13
How much of this is due to fluctuations in the deconfined medium rather than bound states ? Comparison of lattice to PNJL (PRD 85, 014004 (2012)) PNJL variations PNJL-MF: pure mean field calculation PNJL-PL: mean field plus Polyakov loop fluctuations PNJL-MC: mean field plus all fluctuations (incl. chiral and Kaon condensate fluctuations) Conclusion: even the inclusion of all possible flucutations is not sufficient to describe lattice data above Tc. There has to be a contribution from bound states
Properties of bound states above T c : Baryon-meson dependence in correlator C. Ratti, Hadronic resonance gas (HRG) calculation: Baryonic bound states dominate at T>190 MeV. Confirmed by lQCD: S. Borsanyi et al., accepted at JHEP arXiv:1112.4416 Upswing in lattice correlator shows that baryon contribution rises with T, but the correlator never turns positive -> the contribution of bound states above T c must be predominantly of mesonic nature until final deconfinement
Simplest experimental verification Yields of strange particles should be enhanced relative to yields of non-strange particles. If the emission is from a state in equilibrium, then the yields of strange particles should result in a higher temperature than the yields of non-strange particles when fitted with a statistical hadronization model (SHM). ALICE has measurements of π , k, p, Λ , Ξ , Ω . 16
SHM model comparison based on ratios including multi-strange baryons R. Preghenella for ALICE SQM 2012 arXiv:1111.7080 Acta Phys. Pol. 17
SHM model comparison based on yields including multi-strange baryons 152 148 154 160 164 Data: L.Milano for ALICE (QM 2012) Fit: RB 18
An additional idea: Higher order susceptibilities related to cumulants in statistical measurements Susceptibility ratios have the advantage that the volume term in lattice QCD cancels out. They can also be determined experimentally quite easily. And they were proposed as a model independent measure of the chemical freeze-out temperature by Karsch (arXiv:1202.4173) at µ=0. At µ=0 the higher order expansion terms are zero, therefore χ 2 ~ c2, χ 4 ~ c4, χ 6 ~ c6, etc. Experimentally: susceptibility ratios = higher moment ratios of net multiplicity distributions 19
What do we want to measure ? Lattice QCD prediction (RB, S. Borsanyi, Z.Fodor, S. Katz, C.Ratti, arXiv:1305.6297) Problem: Flatness of curves below T c How many states do we need to measure ? : An ongoing project between the UH experimental group and the Torino theory group 20
Can we just measure a subset of states ? HRG calculations are very sensitive to particle composition Light, up and strange quark susceptibility contributions (from Ratti & Bluhm) 21
Lattice QCD flavor susceptibility predictions And then there was charm....... C. Ratti et al., QM 2012 A mixed phase of degrees of freedom ? LHC evolution: T init ~ 650 MeV T dyn.part. = 650-250 MeV T mixed = 250-150 MeV T hadr < 150 MeV Inflection points: 148,164, 250 MeV ....clearly a quark mass effect, but is it relevant for the hadronization behavior of the flavor ? 22
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