elliptic flow results from star · 22 22 < + • in non central ... michael k. mitrovski...

Elliptic flow results from STAR

Michael K. Mitrovski RHIC&AGS Users‘ Meeting - BNL - June 2010

Michael K. Mitrovski RHIC&AGS Users‘ Meeting - BNL - June 2010 2

Outline

1. Introduction. 2. The STAR experiment.3. Search for signals in the energy and system size dependence of elliptic flow to study the phase diagram of strongly interacting matter

a. Looking for signatures for the partonic degrees of freedom (PDoF)

b. Phase transition (PT): Softest Point of the EoS

4. Summary and Conclusions.


Elliptic Flow

x

yz

1. Introduction

Heavy Ion collision Partonic phase Hadronic phase

• Elliptic flow is sensitive to the early stage of collision dynamics.

⇒ A unique hadronic probe of the early stage

vppy

x2

12 = = tan cos ,

= y x

y x

2 2

2 2+

• In non central collisions the coordinate space configu- ration is anisotropic, but the initial momentum distri- bution is isotropic. • Interaction among consti- tuents generate a pressure gradient which transforms the initial coordinate space anisotropy into the observed momentum space anisotropy → anisotropic flow


• TPC: Q, x, p, dE/dx• TOF: time of flight

• π±, K± and p : dE/dx in TPCs• K0, Λ, Ξ, Ω : decay topology + inv. mass. + dE/dx• φ : inv. mass. + dE/dx

s

The STAR Experiment

→ →

2. The STAR experiment

TPC

TOF

FTPC

STAR Ref.: K. H. Ackermann et al.: NIM A 499 (2003) 624


Scenarios for Partonic Matter and Phase Transition3. Signals to discover PDoF and PT

a) Partonic degrees of freedom

b) Phase transition

• Do we see partonic collectivity at top RHIC energies?

• Does ideal hydrodynamic work at RHIC energies?

• Is NQ scaling only a geometry effect?


Partonic Collectivitya. Partonic degrees of freedom

Hadronic collectivity

Heavy Ion collision

Partonic collectivity

• Collectivity develops on the quark level and persists on the hadron level after hadronization.

• Collectivity develops on the hadronic level and will be different for every hadron species due to their cross- section.


Partonic Collectivity

STAR Ref.: S. Shi for the STAR Collaboration: NPA 830 (2009) 187

• At low pt (≤ 2 GeV/c) hadronic mass ordering effect is visible.

• At high pt (> 2 GeV/c) number of quarks ordering.

⇒ Collectivity develops at the partonic stagePHENIX: Issah and Tarenko, nucl-ex/0604011NQ inspired fit: Dong et al., PLB 597 (2004) 328

PHENIX: open symbols

a. Partonic degrees of freedom


Partonic Collectivitya. Partonic degrees of freedom

S0K

0-80% most central

0-80% most central

0-60% most central

Au Au sNN+ , = 62.4 GeVAu Au sNN+ , = 200 GeV

Cu Cu sNN+ , = 200 GeV• v2 of light and multi-strange hadrons are scaling by the number of quarks

⇒ also visible for Φ and Ω which indicates that the collectivity develops at the partonic level

Event plane method (TPC)


Event plane method (FTPC)

STAR Ref.: B. I. Abelev et al.: PRC 75 (2007) 054906 B. I. Abelev et al.: PRC 99 (2007) 112301 B. I. Abelev et al.: PRC 77 (2008) 054901 B. I. Abelev et al.: PRC 81 (2010) 044902


Ideal Hydrodynamicsa. Partonic degrees of freedom

Huovinen et al.:ARNPS 56 (2006) 163Huovinen priv. communication 2003, 2006

Au Au sNN+ , = 200 GeV


• Ideal hydrodynamics fails to describe the data

- Missing of v2 fluctuations?- Viscosity (non-zero η/s)?- Incomplete thermalization?

STAR Ref.: B. I. Abelev et al.: PRC 77 (2008) 054901


Ideal Hydrodynamicsa. Partonic degrees of freedom

Huovinen et al.:ARNPS 56 (2006) 163Huovinen priv. communication 2003, 2006


• Ideal hydrodynamics fails to describe the data

- Missing of v2 fluctuations?- Viscosity (non-zero η/s)?- Incomplete thermalization?

Cu Cu sNN+ , = 200 GeVEvent plane method (FTPC)


Centrality Dependencea. Partonic degrees of freedom

Au+Au collisions

• v2 scaled by the eccentricity to remove initial geometry effects.

• No εpart scaling is observed.

• v2/εpart is larger for central collisions compared to peripheral ones which indicates stronger collectivity in central collisions.⇒ scaling by the number of quarks is visible for all centralities

Event plane method (TPC) Event plane method (TPC)



Scenarios for Partonic Matter and Phase Transition3. Signals to discover PDF and PT


b) Phase transition

• Will we see a change of the EOS in the RHIC Beam Energy Scan (BES)?


Signatures for a Phase Transition - BES Program

y

v2

b. Phase Transition

• At the phase transition from hadronic matter to quark-gluon plasma the EOS is softer in a mixed phase.

• This should be visible in a deep minimum of proton v2 at midrapidity known as softest point.

Stöcker:NPA 750 (2005) 121Kolb et al.:PRC62 (2000) 054909



y

v2

b. Phase Transition




• Hydro calculation shows a minimum for the elliptic flow when passing through a change of the EOS from hadronic matter to quark-gluon plasma.



y

v2

b. Phase Transition





/A (GeV)beamE

-110 10 310 410

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Fopi (prelim.)

EOS

E895

E877

CERES

NA49

STAR

Phenix

Phobos

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in-plane



y

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b. Phase Transition





/A (GeV)beamE

-110 10 310 410

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Fopi (prelim.)

EOS

E895

E877

CERES

NA49

STAR

Phenix

Phobos

out-ofplane

in-plane

• The breaking of v2 number of quark scaling will indicate a transition from partonic to hadronic world.⇒ Important to measure multi-strange particles especially Ω and ϕ v2


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b. Phase Transition

Alt:PRC 68 (2003) 034903

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p0 0.5 1 1.5 2 2.5

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0.2-+h+h

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Au+Au 9.2 GeV (0-60%) Pb+Pb 8.8 GeV (0-43.5%)

Au Au sNN+ , = 9.2 GeV


• Analysis of v2 results for charged and PID hadrons are ongoing.

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BES Program

• v2 results from 9.2 GeV test run with 3k good events.



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b. Phase Transition

Alt:PRC 68 (2003) 034903

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p0 0.5 1 1.5 2 2.5

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0.2-+h+h

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Au+Au 9.2 GeV (0-60%) Pb+Pb 8.8 GeV (0-43.5%)



• Analysis of v2 results for charged and PID hadrons are ongoing.

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BES Program

• v2 results from 9.2 GeV test run with 3k good events.


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Summary and Conclusions


b) Phase transition

• NQ scaling works for Au+Au √sNN = 62.4/200 GeV and Cu+Cu at √sNN = 200 GeV collisions.

• Ideal hydrodynamics fails to reproduce the data from Au+Au and Cu+Cu collisions.

• v2/εpart shows larger v2 for central compared to periheral collisions

• The EOS will be softer in a mixed phase. This should be visible:

- Collapse of proton v2 at midrapidity

- Minimum of v2 for charged particles when trespassing a change of the EOS

• v2 NQ scaling will break in a hadronic scenario.

⇒ scaling by the number of quarks is visible for all centralities

The End and Thanks for

Your Attention

elliptic flow results from star · 22 22 < + • in non central ... michael k. mitrovski...

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