Can flavor hierarchy in the QCD phase transition change our - - PowerPoint PPT Presentation

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)

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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

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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 RAA (hadro-chemistry or flavor change) ? This is not simple partonic energy loss.

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Two distinctly different hadronization processes (both postulated in 1977)

More likely in vacuum ? (non-equilibrium) More likely in medium ? (equilibrium)

Non-equilibrium modeling of hadronization using light cone variables

Inside-outside cascade (Lorentz boost) τo ~ 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

Outside-inside Cascade (energy conseervation) large z (=ph / pq)  short formation time

• C. Markert, RB, I. Vitev

(PLB 669, 92 (2008))

The formation time of hadrons

(for parton fragmentation in medium)

 Can a hadron form inside the deconfined medium above

Tc ?



Three Scenarios:



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 RAA of baryons and mesons (mh difference = formation time difference).

A parton traverses the medium and fragments outside A parton converts into a pre-hadronic state or a quasi-particle which traverses the medium and fragments outside. Color transparency of color neutral objects to colored medium. A parton fragments inside the medium

The formation time of hadrons

(for parton fragmentation in medium)

 Can a hadron form inside the deconfined medium above

Tc ?



Three Scenarios:



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 RAA of baryons and mesons (mh difference = formation time difference).

A parton traverses the medium and fragments outside A parton converts into a pre-hadronic state or a quasi-particle which traverses the medium and fragments outside. Color transparency of color neutral objects to colored medium. A parton fragments inside the medium

 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 ?)

Quasi-particle or hadronic bound state - Is there a difference ?

B/M ratio at intermediate transverse momentum shows baryon anomaly (baryons enhanced by a factor three relative to pp) Recombination in medium Fragmentation in vacuum baryon meson

Does this make sense near the QCD phase transition ?

A re-interpretation of the Polyakov Loop calculation in lattice QCD

survival formation

RB et al., PLB691 (2010) 208 Data: Bazavov et al., arXiv:1105:1131

 Low energy collisions

(AGS, SPS, RHIC scan, FAIR): survival of resonant states

 High energy collisions

(RHIC, LHC): formation of pre-hadronic states

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.

The conclusions are: A.) that the transition is an analytic crossover for an extended range of temperatures (ΔT 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

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Difference between light and strange flavor

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

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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 Tc: Baryon-meson dependence in correlator

Upswing in lattice correlator shows that baryon contribution rises with T, but the correlator never turns positive -> the contribution of bound states above Tc must be predominantly of mesonic nature until final deconfinement

• 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

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.

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SHM model comparison based on ratios including multi-strange baryons

• R. Preghenella

for ALICE SQM 2012 arXiv:1111.7080 Acta Phys. Pol.

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SHM model comparison based on yields including multi-strange baryons

Data: L.Milano for ALICE (QM 2012) Fit: RB 148 164 160 154 152

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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.

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At µ=0 the higher order expansion terms are zero, therefore χ2 ~ c2, χ4 ~ c4, χ6 ~ c6, etc. Experimentally: susceptibility ratios = higher moment ratios of net multiplicity distributions

What do we want to measure ?

Problem: Flatness of curves below Tc How many states do we need to measure ?: An ongoing project between the UH experimental group and the Torino theory group

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Lattice QCD prediction (RB, S. Borsanyi, Z.Fodor,

• S. Katz, C.Ratti,

arXiv:1305.6297)

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Light, up and strange quark susceptibility contributions (from Ratti & Bluhm)

Can we just measure a subset of states ?

HRG calculations are very sensitive to particle composition

Lattice QCD flavor susceptibility predictions

And then there was charm.......

• C. Ratti et al., QM 2012

....clearly a quark mass effect, but is it relevant for the hadronization behavior of the flavor ?

22 Inflection points: 148,164, 250 MeV

A mixed phase of degrees of freedom ? LHC evolution: Tinit ~ 650 MeV Tdyn.part. = 650-250 MeV Tmixed= 250-150 MeV Thadr < 150 MeV

Is the charm curve relevant at the LHC ?

Only if charm is in chemical equilibrium at T = 250 MeV and at least in part thermally produced Charm is predominantly produced in first collisions (gluon-gluon interactions) But, assuming Tinit ~>600 MeV and Tch = 250 MeV, there might be finite contribution from equilibrated phase. Theory: Redlich, Stachel, et al.: thermal production is negligible Rafelski et al.: charm is over-abundant (hep-ph/0605307) Zhang, Ko, Liu: thermal production significant (arXiv:0709.1684) Experiment: Charm v2 & RAA: hints of equilibration Even is charm is not thermally produced but thermalizes along the way then the yields might not be affected but the pT-spectrum should still show the effect.

Summary / Conclusions

• High precision (continuum limit) lattice QCD predicts flavor separation in the

crossover from the partonic to the hadronic matter.

• There are indications, when comparing to hadron resonance gas and PNJL

calculations, that this could lead to a short mixed phase of degrees of freedom in which strange particle formation is dominant.

• If the abundance of strange quarks is sufficiently high (LHC) this should lead to

enhancements in the strange hadron yields (evidence from ALICE) and it could lead to strangeness clustering (dibaryons, strangelets) in case the strange ground state is preferred.

• It could also lead to hyper-nuclei, either through direct production or more likely

through enhanced coalescence in the hadronic phase (evidence from STAR and ALICE).

• A new experimental verification method for flavor separation can be devised by

measuring the higher moments of the strangeness production in comparison to light quark production. Effect in charm sector might be dramatic (mixed phase of degrees of freedom from T = 250 MeV down to 150 MeV).

• The translation of the lattice susceptibilities ratios to higher moments of measured

multiplicity distributions is not trivial but possible. It needs exact mapping of the measurable states.

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