1

Low energy scan and collective flow at 9 GeV

Jiayun Chen , Feng Liu, Shusu Shi, Kejun Wu

Weihai , Aug. 9,2009

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Outline

Motivation

Collectivity from STAR at 9.2GeV

MC Simulation at 9 GeV

Summary and Outlook

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Motivation

RHIC beam energy scan program :

----- Search for critical point.

----- Draw the QCD phase boundary.

QCD Phase diagramCro

ss o

ver

At RHIC:(1) pT-NQ scaling

(2) partonic collectivity

(3) deconfinement

hot and dense matter with partonic collectivity has been formed at RHIC

QM09 : SS Shi (STAR Collaboration)

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Access to large range of and T

Beam Energy Scan (BES) at RHIC + SPS + FAIR

RHIC:

advantage of collider mode !

At fixed target geometry:

detector acceptance changes with energy

track density at mid-y increases fast with energy

-> technical difficulties in tracking

Motivation

9.2 GeV 9.2 GeV

Collider Acceptance

√sNN

6 GeV

17 GeV

√sNN = 9.2 GeV Au+Au Collisions at RHIC

Fix

-tar

get

Mod

e N

A49

C

ollid

er M

ode

ST

AR

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RHIC run 10 (fall 2009)

sNN [pft]

GeV [GeV/c]

B

[MeV]<BBC Rate>

[Hz]

Days/

Mevent

# events # beam days

4.6 [9.6] 570 3 9 5M 45

6.3 [18.8] 470 7 4 5M 20

7.6 [27.9] 410 13 2 5M 10

8.8 [37.7] 380 20 1.5 5M 7.5

12 [71.0] 300 54 0.5 5M 2.5

18 [161] 220 >100 0.25 5M 1.5

28 [391] 150 >100 0.25 5M 1.5

(1) Large energy range accessible(2) Collider geometry (acceptance won’t change with S, track density varies slowly)(3) STAR detectors well suited (large acceptance), tested & understood

STAR PAC 2007 Strawman proposal:

Note: NA61 @ CERN (starting in 2010): 10, 20, 30, 40, 80, 158 GeV/c

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STAR TPC image of 9 GeV Au+Au, taken on June 7, 2007 (run 8158119, ev.44), figure from Jeff Langraf

2001: 19.6 GeV Au+Au2004: 22.4 GeV Cu+Cu2007: 9 GeV Au+Au

observed apparent rates of collisions surprisingly high (?!)

to do: (1) understand background

(2) optimize triggering

STAR experience with Low Energy RHIC running

Collectivity from STAR at 9.2GeV

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STAR Experiment and Collisions at Ecm= 9.2 GeV

Excellent Particle IdentificationCollisions recorded in STAR TPC

Analysis based on ~ 3000 good events collected at ~ 0.7 Hz in year 2008

PID will further strengthen with the completion of ToF

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Azimuthal Anisotropy - Directed Flow

v1 vs. η show different trend between the high and low energy because that the spectator rapidity decreases with incident energy

QM09 Poster : Jiayun Chen (STAR Collaboration)

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Azimuthal Anisotropy - Elliptic Flow

QM08 Lokesh Kumar for STAR

With TOF, the pt region will be extended to a higher value.

Important to perform the v2 scaling analysis.

v1 in AMPT

• low energy: – the default AMPT with low-NTMAX consistent with the

STAR results.– The melting AMPT seems difficult to describe the data.

QM09 Poster : Jiayun Chen

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MC Simulation at 9 GeV V2 of all Charged Hadrons

About 3231k, 862k, 4370k and 4507k events are used for minibias calculations at UrQMD v2.3 , RQMD v2.4, AMPT v2.1 with string melting and default.

v2 : AMPT with melting > AMPT default > UrQMD >RQMD.

Partonic reactions enhance hadrons v2 !

v2 value at AMPT with melting is about equal to the default at center rapidity, but much larger v2 at high rapidity area – connection to the observed RIDGE:

Early partonic interactions are important!

Only 3k good events for experimental data.

Difficult to say which MC model is best suitable.

MC vs. Experimental data

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v2 NQ Scaling in AMPT

Only for AMPT with string melting

like hydrodynamic behavior

mass ordering at pT<1.2GeV/c

Obvious hadrons type dependence: NQ Scaling at

pT>1.2GeV/c

Crossing and subsequent splitting between meson and baryon at pT~1.2GeV/c

Why is the v2 NQ scaling presented in the AMPT with string melting?

Difference for two AMPT versions

Quark coalescence mechanism leads to v2 NCQ scaling

Zi-Wei Lin,Che Ming Ko,etc., Phys.Rev.C 72,064901(2005),

“Multiphase transport model for relativistic heavy ion collisions ”

wukj@iopp.ccnu.edu.cn17

Default AMPT

The breaking of v2 NQ scaling. The partons cross section almost doesn’t affect v2 value.

AMPT with string melting

The excellent v2 NQ scaling. Large partons cross section leads to strong v2.

The strength of the final hadron v2 is directly related to the partons cross section!

Partons Cross Section vs. Hadrons v2

The broken NQ scaling behavior maybe indicates the phase transition from dominant partonic to hadronic matter!

wukj@iopp.ccnu.edu.cn18

v2 in RQMD and UrQMD

The v2 NQ scaling may not be the unique feature of quark coalescence !

Hadronic interactions -> rough v2 NQ scaling

The same v2 NQ scaling as AMPT with SM.

may be statistical fluctuation?

(no light quark component)

is very important for studying the medium properties.

KK

ss dominant partonic matter

dominant hadronic matter

v2 from KKbar fusion will not obey the v2 NQ scaling.

Additive Quark Model

cross section only depends on the quark-content of the colliding hadrons

3/2

21

039.0

)4.01)(4.01()3

2(40

totel

ssntot xxM

Color Strings and ropes -excitation and -fragmentation

MhqhBhqqhBhqh 2

1,

3

2,

3

1

dtyxAdpyxtppv tt tt ),(),,,(),()(2

denotes the hyper-surface where hadrons are emitted.In the low pt region, frequent rescatterings among hadrons can lead to hydrodynamic-like mass ordering.

In the higher pt region (pt>1.5GeV/c), particles early freeze out and lack the hydrodynamics development, and the details of the interaction cross-sections are most important.

elliptic flow:

Where does v2 NCQ Scaling Come from?

3

2

B

M

3

2

B

M

Y.Lu,F.Liu,N.Xu.etc., J. Phys. G: Nucl. Part. Phys. 32 (2006) 1121–1129,

K. Goulianos, Phys.Rep.101,169(1983),“Diffractive interactions of hadrons at high energies ”

S.A.Bass, M.Belkacem,etc., Nucl-th/9803035, “Microscopic Models for Ultrarelativistic Heavy Ion Collisions”

The hadronic cross sections in UrQMD can been parameterized by AQM.

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Summary and Outlook

STAR will measure : yields and particle ratios T vs

particle spactra (pt, rapidity, …),

strangeness production (K/, multistrange, …),

fluctuations and correlations

flow (v1,v2,v4, …) with charged and identified particles,

HBT radii, …

Search for : - disappearance of partonic activities

- onset of critical phenomena: fluctuations, correlations

1) turn on and off signature of de-confinement (QGP)

2) High statistics is required for v2 in the further experiments.

The unique RHIC energy scan program will map the QCD diagram in sNN =5-50 GeV, (corresponding to μB ~ 600-150 MeV)

Thank you

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sNN (GeV) for Au+Au # weeks in 25-cryoweek scenario # weeks in 30-cryoweek scenario

200 10 10

62.4 4 4

39 1.5 1.5

27 2.5 4.5

18 0 1.5

11.5 2.0 2.5

7.7 0 1.0

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Azimuthal Anisotropy - Directed Flow

v1 vs. η show different trend between the high and low energy because that the spectator rapidity decreases with incident energy

QM09 Poster : Jiayun Chen (STAR Collaboration)

Difference for two AMPT versions

Quark coalescence mechanism leads to v2 NCQ scaling

Energy scan of v1 at RHIC energy

• Centrality dependence:– high energy: clearly

dependence– lower energy: seems to be

weaker• V1(y) of charged particle

from AMPT seems consistent with the RHIC data in sharp– high energy: melting AMPT– low energy: default AMPT

• The directed flow wiggle from peripheral to central:– high energy: more clearly

transformation– low energy: weak effect by

centrality but clearly wiggle• The direction of v1 seems

consistent in different energy in mid-rapidity.

Motivation

flow

antiflow

Brachmann, Soff, Dumitru, et. al. , PRC 61 (2000) 024909.L.P. Csernai, D. Roehrich PLB 458, 454 (1999) M.Bleicher and H.Stocker, PLB 526,309(2002)

Anti-flow/3rd flow component, with QGP v1 flat at middle rapidity.

Directed flow (v1) and phase transition