Marcus Bleicher, Florence 2006

Longitudinal Flow and Onset of DeconfinementLongitudinal Flow and

Onset of Deconfinement

Marcus Bleicher

Institut für Theoretische Physik

Goethe Universität Frankfurt

Germany

Marcus Bleicher, Florence 2006

Outline of the talkOutline of the talk

• Introduction

• Fluctuations Evidence for mixing

• Rapidity widths + Landau softest point

• Summary

Marcus Bleicher, Florence 2006

The tool: UrQMDv2.2The tool: UrQMDv2.2

• Non-equilibrium transport model• Hadrons and resonances• String excitation and fragmentation• Cross sections are parameterized

via AQM or calculated by detailed balance• pQCD hard scattering at high energies

• Generates full space-time dynamics of hadrons and strings

Marcus Bleicher, Florence 2006

Thanks to the UrQMD group@ Frankfurt

Thanks to the UrQMD group@ Frankfurt

• Sascha Vogel (Resonances)

• Stephane Haussler (Event-by-Event Fluctuations)

• Hannah Petersen (Flow at FAIR)

• Diana Schumacher (Di-Leptons)

• Qingfeng Li (Isospin Dynamics & HBT)

• Xianglei Zhu (Elliptic Flow and Charm)

• Mohamed Abdel-Aziz (Event-by-Event Fluctuations)

• Elena Bratkovskaya (HSD)

• and Horst Stoecker (keeping it running)

Marcus Bleicher, Florence 2006

MotivationMotivation

At RHIC: look for signals of freely moving partons.

At FAIR/SPS:look for the mixed phase and the onset of deconfinement

E. Bratkovskaya, M.Bleicher. et al., PRC 2005

Marcus Bleicher, Florence 2006

Excitation functions: ratios

Excitation functions: ratios

• ‘Horn’ in the ratio not reproduced

• well reproduced

• relative strange baryon enhancement reproduced

/K

/K

/

E. Bratkovskaya, M.Bleicher. et al., PRC 2005

Marcus Bleicher, Florence 2006

• K/ fluctuations increase towards lower beam energy– Significant enhancement over hadronic cascade model

• p/ fluctuations are negative– indicates a strong contribution from resonance decays

NA49 Preliminary NA49 Preliminary

Fluctuation studies

Tak

en f

rom

Ch

risto

ph

Rol

and

Marcus Bleicher, Florence 2006

Energy dependenceEnergy dependence

H. Petersen, X. Zhu, M.B.

• Qualitative description OK

• Importance of potentials at low energies

• Lack of pressure shows up at SPS energies

• EoS <-> Flow

Marcus Bleicher, Florence 2006

‘Partonic’ dof already atlow SPS energy

‘Partonic’ dof already atlow SPS energy

•Breakdown of v2 in model coincides with onset of ‘partonic’ matter

signals onset of change of EoS in the early stage

30 AGeV

H. Petersen, X. Zhu, M.B.

Marcus Bleicher, Florence 2006

Stopping power

Stopping power

• Linear increase of rapidity shift at low energies

• ‘Saturation’ above highest SPS energy

• However, relative momentum loss is energy independent

UrQMD vs data

Pb+Pb/Au+Au

Marcus Bleicher, Florence 2006

• Multiplicities• Temperatures• Elliptic Flow• Correlations

have already been studied

Can we learn more from the longitudinal dynamics?

Marcus Bleicher, Florence 2006

Multiplicity fluctuationsMultiplicity fluctuations

Extraction of the multiplicity distribution for every Npar

Note: Calculation is narrower than the data for Npar~45

Pb+Pb (158 AGeV)

in the NA49 acceptance

(1.1<yCM<2.9)

Marcus Bleicher, Florence 2006

• The fluctuation is quantified with the

scaled variance :

• Enhanced fluctuations for mid-

peripheral collisions are observed

Multiplicity fluctuations at SPS:The problem

Multiplicity fluctuations at SPS:The problem

NNVar

NNNVar

)(

)(22

Note : - for a poisson distribution, w=1Similar results from HIJING, HSD and RQMD

Marcus Bleicher, Florence 2006

Where is the problem?Where is the problem?

Pb+Pb (158 AGeV)

in the NA49 acceptance

(1.1<yCM<2.9)• Mean value correctly reproduced

• Variance reproduced for central and very peripheral events

• Failure for mid-peripheral events

Marcus Bleicher, Florence 2006

Analysis of different windowsAnalysis of different windows

the normalized variance :

• flat in the projectile hemisphere

• larger in the mirror acceptance

• even larger in 4

• maximum around Np=40

Konchakovski, Haussler,…, PRC 73 (2006)

Marcus Bleicher, Florence 2006

Fluctutions in target regionFluctutions in target region

• the fluctuation has a maximum

around Np=25

• introduces an asymetry between

projectile and target participants

• leads to an increase of the multiplicity

fluctuation in the target hemisphere

NNVart

part

t

partt

P arg

arg

arg )(

Marcus Bleicher, Florence 2006

Correlation length in rapidityCorrelation length in rapidity

Rapidity window dependence :

• correlation length of the order of 1

unit of rapidity

• target and projectile hemisphere are

independent in hadron-string models

Marcus Bleicher, Florence 2006

Mixing and fluctuationsMixing and fluctuations

M. Gazdzicki and M. Gorenstein:arXiv:hep-ph/0511058

• I.e. the trigger condition ‘marks’ projectile and target participants

• This allows to study the degree of mixing of the matter produced in HIC

• Data suggest strong mixing of hemispheres

Hints to expanding initial fireball in contrast to string dynamics

Marcus Bleicher, Florence 2006

What the fluctuations told us…What the fluctuations told us…

• Initial fireball of newly produced particles

• Fireball seems to expand Landau-like

• Leads to strong correlations in rapidity

We might use Landau-type hydro to explore the properties of this matter

Marcus Bleicher, Florence 2006

Pion rapidity densityPion rapidity density

• Pions rapidity densities are Gaussians at all energies

D. Ouerdane, QM04D. Ouerdane, QM04

Marcus Bleicher, Florence 2006

Different particle typesDifferent particle types

• NA49 data yields Gaussian rapidity distributions

• Also ALL other experiments report Gaussians for newly produced particles

Marcus Bleicher, Florence 2006

Fireball expansionFireball expansion

• Assumptions:- applies only to newly produced particles

- Lorentz contracted nuclei

- simplified Hagedorn gas EoS

E. Shuryak, Yad. Fiz. 16 (1972) 395

similar to Landau hydro

For more praise on Landau hydro see. P. Steinberg

Marcus Bleicher, Florence 2006

Rapidity widthsRapidity widths

• Rapidity width scales linearly with projectile rapidity

M. Bleicher, hep-ph/0509314

Marcus Bleicher, Florence 2006

Speed of soundSpeed of sound

• Analysis of the rapidity data indicates a softest point at20-30 AGeV beam energy

M. Bleicher, hep-ph/0509314

Marcus Bleicher, Florence 2006

Its soft, but…Its soft, but…

• …is it the mixed phase?

• UrQMD also describes the rapidity widths

• UrQMD has a soft equation of state

Marcus Bleicher, Florence 2006

SummarySummary

• Fluctuations indicate strongly mixed initial stage

• Assumption of Landau-type hydro allows to extract speed of sound from rapidity widths

• Apparent local minimum of sound velocity around 20 – 30 AGeV

• Nature of this softest point is unclear