marcus bleicher, etd, montreal 07/2007 elliptic flow and fluctuations in heavy ion collisions marcus...

Marcus Bleicher, ETD, Montreal 07/2007

Elliptic Flow and Fluctuations in Heavy Ion collisions

Elliptic Flow and Fluctuations in Heavy Ion collisions

Marcus Bleicher

Institut für Theoretische Physik

Goethe Universität - Frankfurt

Germany

Marcus Bleicher, ETD, Montreal 07/2007

Thanks to the UrQMD group@ Frankfurt

Thanks to the UrQMD group@ Frankfurt

• Sascha Vogel (Resonances and di-leptons)

• Katharina Schmidt (Di-leptons)

• Stephane Haussler (Event-by-Event Fluctuations)

• Hannah Petersen (Flow)

• Daniel Krieg (Recombination)

• Qingfeng Li (HBT)

• Xianglei Zhu (Charm)

Marcus Bleicher, ETD, Montreal 07/2007

ContentsContents

• Introduction

• v1 and v2

• v2 fluctuations

• Summary

Marcus Bleicher, ETD, Montreal 07/2007

MotivationMotivation

At RHIC: look for signals of partonic matter. (large v2, hydro)

At critRHIC/SPS:look for the mixed phase and the onset of deconfinement(flow stalls, large fluctuations, ideal hydro breaks down)

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

Marcus Bleicher, ETD, Montreal 07/2007

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, ETD, Montreal 07/2007

MultiplicitiesMultiplicities

Comparison to data over the whole energy range

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

Marcus Bleicher, ETD, Montreal 07/2007

Droplets: > 10-100 (Mishustin)

Taken from a talk by B. Lungwitz at CPOD 2007

UrQMD data from Lungwitz& Bleicher, arXiv:0707.1788

Marcus Bleicher, ETD, Montreal 07/2007

Maybe HBT can deliver…Maybe HBT can deliver…

• long life times in the mixed phase…

Rischke, Gyulassy, Nucl.Phys.A608:479-512,1996

~ Energy density

10 fold increase in life time during the mixed phase

Marcus Bleicher, ETD, Montreal 07/2007

The HBT puzzle? The HBT puzzle?

• Model calculations of RO/RS or (RO2-RS

2)1/2 are usually larger than the experimental data

Duration time (in the absence of flow):

2

22 )(

SO RR

No indication of long life time in the data

1 10 100 1000 100000

2

4

6

8

(R2 O-R

2 S)1/

2 (fm

)

Eb (A GeV)

Circles: kT=100 MeV/c

Squares: kT=200 MeV/c

Stars: exp. data

Li, Bleicher, Stoecker, arXiv:0706.2091. JPG in press

Marcus Bleicher, ETD, Montreal 07/2007

Flow is important!Flow is important!

• Many observables never fullfilled the promise HBT, fluctuations, J/Psi,… ideally one should be able to study them at all energies

Transverse collective flow is intimately connected to pressure

Flow is sensitive to changes in the equation of state and therefore to phase transitions (H.Stöcker,W.Greiner Phys.Rep. 137 (1986) 277)

Marcus Bleicher, ETD, Montreal 07/2007

Introduction - directed flowIntroduction - directed flowFourier expansion of the azimuthal distribution of the emitted particles :

t

x

p

pv 1

1

cos212

1

iRi

tttt

ivdydpp

dN

dyddpp

dN

Directed flow

measures the total amount of transverse flow

22yxt ppp with

Reaction planeReaction plane

(J.Y. Ollitrault, Phys. Rev. D, 46; A.M. Poskanzer, S.A. Voloshin, Phys. Rev.

C, 58)

Marcus Bleicher, ETD, Montreal 07/2007

Excitation function Excitation function

1-fluid hydro prediction for pxdir :

softest point in the EoS leads to decreasing flow

from D.Rischke, Y.Pürsün et al. (Heavy Ion Physics 1,309,1995)

Marcus Bleicher, ETD, Montreal 07/2007

Antiflow around midrapidityAntiflow around midrapidity

(L.Csernai, Phys.Lett. B 458, 1999)

(J.Brachmann et al., Phys.Rev. C, 61, 2000)

Prediction of antiflow if QGP is produced softening of the EoS leads to flow in the „wrong“ direction

Marcus Bleicher, ETD, Montreal 07/2007

A problem with hydroA problem with hydro

• Hydro is not a good tool to study the onset of deconfinement

• Agreement at top RHIC energies with ‘wrong’ EoS and ‘wrong’ initial c.(see talk by Dumitru)

try transportHeinz, Kolb,STAR

Marcus Bleicher, ETD, Montreal 07/2007

v1 of protons @ 40 AGeVv1 of protons @ 40 AGeV

Comparison of rapidity spectra between model and data:

Largest flow at high rapidity values

Centrality dependence visible

Data

fro

m C

.Alt

et

al.,

Ph

ys.

Rev.

C 6

8,

200

3

Petersen et al, Phys.Rev.C74:064908,2006

Marcus Bleicher, ETD, Montreal 07/2007

v1 of protonsv1 of protons

Slope around midrapidity characterizes shape of the rapidity distribution

Extracted from normalized rapidity distribution via polynomial fit

At low energies: potentials are important

At high energies: data developes negative slope ´wiggle´

QGP-signal? (L.P. Csernai, Phys.Lett. B 458,1999)

Petersen et al, Phys.Rev.C74:064908,2006

Marcus Bleicher, ETD, Montreal 07/2007

Time evolutionTime evolutionPressure Pressure gradients Elliptic flow

Petersen et al, Phys.Rev.C74:064908,2006

Marcus Bleicher, ETD, Montreal 07/2007

Time evolution at RHICTime evolution at RHIC

Elliptic flow builds up in the hadronic stage of the collision

High-pt

Low-pt

Y.

Lu e

t al

, J.

Ph

ys.G

32:1

121-

1130

,200

6

Marcus Bleicher, ETD, Montreal 07/2007

v2 (y) of pions @ 40/160 AGeVv2 (y) of pions @ 40/160 AGeV

Pb+PbPet

erse

n et

al,

Ph

ys.R

ev.C

74:0

6490

8,20

06

Marcus Bleicher, ETD, Montreal 07/2007

v2(y) of protons @40 AGeVv2(y) of protons @40 AGeV

Collapse of elliptic flow?(H.Stöcker, Nucl.Phys. A 750, 2005)

Experimental situation unclear

Transport model calculation is compatible with the data

Petersen et al, Phys.Rev.C74:064908,2006

Marcus Bleicher, ETD, Montreal 07/2007

Energy dependenceEnergy dependence

• Qualitative description OK

• Importance of potentials at low energies

• Lack of pressure shows up at lower SPS energies

Pet

erse

n et

al,

Ph

ys.R

ev.C

74:0

6490

8,20

06

Marcus Bleicher, ETD, Montreal 07/2007

v2 fluctuationsv2 fluctuations

• Tilted axis has to be taken into account with proper (participant) definition of eccentricity

Broniowski et al

Marcus Bleicher, ETD, Montreal 07/2007

Additional fluctuationsAdditional fluctuations

• One would expect additional dynamical fluctuations, if the system is not a perfect liquid

• Degree of perfection is quantified by the Knudsen number Kn

S. Vogel et al., nucl-th/0703031

Marcus Bleicher, ETD, Montreal 07/2007

Fluctuation analysisFluctuation analysis

• To strong fluctuations

• Cross section increase, decreases fluctuations

S. Vogel et al., nucl-th/0703031

Marcus Bleicher, ETD, Montreal 07/2007

Extrapolation to small Knudsen numbers

Extrapolation to small Knudsen numbers

• Experimental data requires tiny mean free path

• 1/Kn > 100-1000

Bhalerao, PLB2005

S. Vogel et al., nucl-th/0703031

Marcus Bleicher, ETD, Montreal 07/2007

Only ideal hydro can do itOnly ideal hydro can do it

• Calculation by Kodama et al.,

• Fluctuating initial state from Nexus

• Where is viscosity?

Marcus Bleicher, ETD, Montreal 07/2007

SummarySummary

Flow is the ideal tool to study the onset of deconfinement (critRHIC!)

However, ideal hydro fails below top RHIC energy

Unfortunately, hadron/string transport fails above SPS energies

At top RHIC energy: Elliptic flow fluctuations indicate very short mean free path

No sign of ANY turbulence or dynamical fluctuations