rhic 能区的集体流和能量扫描

1Y.G.Ma Workshop on RHIC Physics and CSR physics, Weihai, 2009/8/9-14

RHIC能区的集体流和能量扫描

马余刚中国科学院上海应用物理研究所

Outline:•Flow Introduction •Results (1): Flow measurements at RHIC•Results (2): Flow Theory•Summary•Outlook


Part I:

Flow Introduction:


Elliptic flow v2 Elliptic flow v2

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zy

px

py

y

x

● Non-central A+A collisions: azimuthally anisotropic distribution of particles in coordinate-space● Density gradients and interactions between the particles: an asymmetry in momentum-space● Signal is self-quenching with time – early time observable! ● Measurement: Fourier expansion of the azimuthal angle (φ-Ψ) distributions

(mid-rapidity)


Azimuthal Distributions

Systematic measurements as a function of particle mass and taking into account time scale

• v0 Radial flow integrated over evolution • v1 Directed flow early• v2 Elliptic flow early• vn ……..

Fourier Analysis of azimuthal particle distribution

v1, v2, vn largest at intermediate impact parameters, zero at b = 0 and b = 2R


Flow (radial, directed and elliptic)

x

y

x

y

z

x

• Only type of transverse flow in central collision (b=0) is radial flow.

• Integrates pressure history over complete expansion phase

• Elliptic flow, caused by anisotropic initial overlap region (b > 0).

• More weight towards early stage of expansion.

• Directed flow, sensitive to earliest collision stage (pre-equilibrium, b > 0)


RHIC

v1,v2,v4

LHC

v1,v2,v4,...

and elliptic flow

2009


Part II:

Flow measurements at RHIC:


Directed flow at RHIC

rapidity

v1

Looking for the ‘wiggle’:

Directed flow is most sensitive to the initial conditions

z

x

Radial flow <x px> > 0

rapidity

px, v1

R. Snellings, H. Sorge, S.V., F. Wang, Nu Xu, PRL 84 (2000) 2803

x

rapidity

px

xBaryon stopping

“ wiggle”

v1 is found being independent of collision systems.

PRL 101, 252301 (2008)


Longitudinal scaling for v1

PHOBOS: Phys. Rev. Lett. 97, 012301 (2006)

1. v1~0 at mid rapidity and decrease with eta till Ybeam, then turnover at larger eta: probably the proton and nucl frag dominate identified hadron v1 requested

2. The same curve for different size system and energyLimiting fragmentation holds for different energies, collision systems and harmonics.

3. No model is successful to reproduce the above scaling: AMPT can only predicted approximate scaling for each colliding species separately. theory to be developed.

STAR: Phys. Rev. Lett. 101, 252301 (2008)

= η - ybeam

Ymid

Pro

ton

& n

ucl f

rag.

dom

inat

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Y.G.Ma Workshop on RHIC Physics and CSR physics, Weihai, 2009/8/9-14

Elliptic Flow

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x

py

px

coordinate-space-anisotropy ⇔ momentum-space-anisotropy

Established by geometry - early timesFirst observed at BEVALAC and at SATURNE

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v2 Excitation Function

Rich structure:

Transition from in-plane to out-of-plane and back to in-plane emission:

Low Ebeam: rotational behavior;Mid Ebeam: squeeze-outHigh Ebeam: pressure-induced in-plane emission

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STAR, PRL90 032301 (2003)

b ≈ 4 fm

“central” collisions

b ≈ 6.5 fm

midcentral collisions

Resulting azimuthal distributionsResulting azimuthal distributions

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STAR, PRL90 032301 (2003)

b ≈ 4 fmb ≈ 6.5 fmb ≈ 10 fm

peripheral collisions

Resulting azimuthal distributionsResulting azimuthal distributions

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STAR, PRL90 032301 (2003)

“v2”

observed momentum anisotropy is largely elliptic deformation; its amplitude is denoted v2

RHIC v2 reaches large values yielded by hydro (unlike lower energies)Hydrodynamiccalculation ofsystem evolution

Elliptic flowElliptic flow

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Low pt: mass splitting

•Ideal hydro can describe the data very well, QGP EoS is a reasonable choice•Blast wave model can also fit the data with a set of four parameters.

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KET = (mT-m0)/nq

PRL. 98, 162301 (2007)

1. Number-of-constituent-quark scaling (meson vs baryon)

2. v2(pT) /nquark vs. KET/nquark becomes one curve independent of particle species.

QuarkMatter2009

NCQ scaling in middle Pt

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Multi-strange particle v2: Partonic Collectivity

Final word on partonic collectivity at RHIC!

STAR data (S. Shi et al)

PHENIX π and p: nucl-ex/0604011v1NQ inspired fit: X. Dong et al. Phy. Let. B 597 (2004) 328-332

J. Zuo, J.Y.Chen,X. Cai, YGM, F. Liu et al., EPJC 55,463(2008)

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High Pt region: non-flow effect, such as partonic Eloss induced correlation

STAR

•Different path-length of parton travserse the medium induced Partonic Eloss azimuthal anisotropy•Data: Au+Au peripheral, dAu, pp similar (left) non-flow correlation•Different methods to subtract the non-flow effects were developed, such as 4-particle correlation

Y.G. Ma, Workshop on RHIC Physics and CSR physics, Weihai, 2009/8/9-14

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Exploring the non-flow in elliptic flow

g0 (hydro dominance), CFB1g1 (jet dominance), CFB0

A backwar-forward v2 correlation provides an experimentally accessible observable which distinguish collective and nonflow contribution.

Liao&Koch, PRL103 (2009)042302

Black solid line: collective flow-only; colored long-dashed: jet-only;Dashed-dotted: weighted contribution (1-g)<v2_F> (black) and g<v2_J> (colored)

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Y.G.Ma Workshop on RHIC Physics and CSR physics, Weihai, 2009/8/9-14QuarkMatter2009

Scaling generally holds in Cu+Cu at 200GeV.Some deviation at more peripheral collisions.

phenix preliminary

KET/nq [GeV/c] KET/nq [GeV/c] KET/nq [GeV/c]

KET/nq [GeV/c] KET/nq [GeV/c]

NCQ Scaling in Small System(PHENIX)

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NQ roughly works at forward rapidity

NCQ Scaling, Forward Rapidity

QM09 talk by S. Sander

BRAHMS Preliminary

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ρ0 v2, Probe Late Stage Dynamics

Long lifetime, balance between daughter rescattering and ρ0 regeneration.Sensitive to dynamics between chemical and kinetic freeze-out.Significant ρ0 v2 observed.(n=2, quark level; n=4, hadronic level; preliminary n=4.7 with large error, no conlusion yet)

QM09 talk by P. Fachini

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Test Hydro in Small System Ideal hydro: P. Huovinen

pT < 2 GeV/c Smaller v2 for heavier

hadrons as expected from hydrodynamics.

Sizable v2(Ξ) even in small system

Ideal hydro fails to reproduce the data

Fluctuation of v2? Viscosity ? Incomplete thermalization ?

STAR preliminary

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v2 in Cu + Cu (Au +Au) at 200 and 62.4 GeV are comparable within statistical errors

v2 at Cu + Cu 62.4 GeV ~ 12.5 M events- Same procedure used for 200 GeV. - Event plane resolution is 0.088 0.004 in 0 - 60 %, about factor 2 smaller than that in 200 GeV due to lower multiplicity.

STAR Au + Au 200 GeV : PRC77, 054901 (2008) Au + Au 62.4 GeV : PRC75, 054906 (2007)

Energy Dependence

STAR preliminary

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STAR preliminary

Au + Au at 200 GeV

Au + Au : PRC77, 054901 (2008)

System Size Dependence

Does v2 in most central reach ideal hydrodynamic limit ?

v2 scaled by eccentricityRemove the initial geometry effect

v2 seems solely depending on initial geometry and number of participant in 200 GeV collisions

v2 ∝ v2(ε, Npart)

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45 curves!

v2 depends not only by the eccentricity, but also by size the collisions

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Centrality dependence of v2

• Partonic transport model can describe the v2(b)• But, a large parton cross section is needed!

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Pseudo-rapidity dependence of v2

v2(eta) roughly agrees with scaling proportional to the charged particle density

hydro+afterburner describe v2(eta) well

v2(eta-ybeam) scaling in frag region limiting fragmentation picture

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STAR preliminary

v2/ε scaling: S. Voloshin (for STAR Collaboration), J.Phys.G34(2007)S883PHENIX π, K and p: nucl-ex/0604011v1CGC eccentricity: H.J. Drescher and Y. Nara, PRC 76 041903 (2007), H.J. Drescher and Y.Nara, PRC 75 034905 (2007)

Ideal Hydro Limit

STAR preliminary

Hydro limitΞΛ p K h

STAR preliminary

Ideal Hydro Limit Even in central Au + Au collisions, fitting results indicate that the

system is still away from hydro limit

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most perfect liquid in the world?; Phys. Rev. Lett. 98, 092301 (2007)

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Effective η/s Extracted from Model

Caveats:Transport model motivated~ best for dilute system of massless particles no phase transition

STAR preliminary

Data shows particle type dependence, not a built-in feature in the modelCan viscous hydrodynamics explain the particle type dependence ? Inferred η/s depends strongly on the eccentricity model

T: π spectra slope 200 MeVR: Glauber or CGC calculation

H. J. Drescher et al, PRC 76 024905 (2007)

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v4/v22 – An Independent Test

v4/v22 ~ 0.5 in Ideal Hydro

Borghini & Ollitrault, PLB 642 227 (2006)

v4/v22 > 0.5 in data

K=0 in Ideal Hydro, K>0.5 in data.

Boltzmann calculation : Gombeaud and Ollitrault, private communication

Preliminary

PHENIX Preliminary

PHENIX Preliminary

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Similar scaling was predicted in Fermi energies: nucleon number scaling & v4/v2^2 scaling

In hydro by Kolb et al, assuming that quarks have no higher-order anisotropic flows

If quarks also flow, one get

Similarly, if v4/v^2 = ½ for nucleon, then V4/v2^2(A=2) = ¼+1/2*1/2=1/2V4/v2^2(A=3) = 1/3+1/3*1/2=1/2This is the case for the right bottom plot!

V2/A vs Pt/A&

V4/V2^2 ~ cst

V4/A^2 vs (Pt/A)^2

It is interesting to check p, d, t, alpha v2,v4 @ RHIC!

T. Yan, YGM et al., PLB 638 (2006)50

p, d, t, alpha

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Light Nuclei v2 at STAR

Baryon v2 -- X.Dong et al, Phys. Lett. B597 (2004) 328

BW parameters:F. Retiere, M. Lisa, Phys.Rev. C70 (2004) 044907

The 1st observation of negative v2 at RHIC.No model describes the data.

d v2 follows A scaling, 3He v2 shows some deviation, need more statistics. => Final state coalescence.

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Heavy Q elliptic flow

• J/ψ flow : possible test of regeneration– Electrons from open c and

b semileptonic decays show nonzero elliptic flow

– J/ψ regenerated from c quarks should inherit their flow

c & b (+ J/ψ)

• Main criticisms– Flow seen at NA50(*) and NA60(**) where net charm yield is not that highFlow seen at NA50(*) and NA60(**) where net charm yield is not that high

• Indication of other causes that induce J/ψ flowIndication of other causes that induce J/ψ flow

• But then...– Absence of J/ψ elliptic flow would weigh against regeneration models which all predict substantial flow

(**) R. Arnaldi@QM08

(*) F. Prino@HP08

PRL 98, 172301 (2007)

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Flow of directed photons

Rich structure of photon flow (Gale et al., PRL96 (2006) 032302; Chatterjee et al., PRL96, 202302 (2006))(1)Thermal photons; (2)photons from high Pt parton fragmentation; (3) Bresstrahlung and jet consvertion etcBresstrahlung photon flow has been also studied in low Ebeam, anti-correlation with proton flow was found. See the following figures. (G. Liu, YGM et al., PLB 663, 312(2008))

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Part III:

Flow Theory:

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Success of ideal hydrodynamics

Ideal hydrodynamics has correctly reproduced the collective behaviour at RHIC when pT<2 GeV/c.

Perfect fluid ! sQGP !

PRL 92 (2004) 052302

How small the values of viscosities will be?

To extract viscosities from experimental data, we need viscous hydrodynamics.

P.F. Kolb and U. Heinz nucl-th/0305084

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What viscosities will do?

Shear viscosity:

-The velocity gradient are directly related to viscous behavior of the fluid

-Viscosities reflect resistance to flow

Bulk viscosity:

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Extract η/s from experimental data:

When extract shear viscosity, bulk viscosity is set to be zero.Should we neglect the bulk viscosity?

M. Luzum and P. Romatschke, PRC 78 (2008) 034915

Glauber 0-0.08 ; CGC 0.08-0.16

shear viscosity effect on v2

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Equations in causal viscous hydrodynamicsConservation law:

Evolution equations for bulk viscous pressure and shear pressure tensor:

bulk viscous pressure shear pressure tensor

Avoid two problems in the first order theory:

causality probleminstabilities Hiscock & Lindblom, PRD 31 (1985) 725

Israel & Stewart, Ann.Phys 118 (1979) 341

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-dissipate to other places at late time

-smaller relaxation time, larger effects

-time averaged bulk viscosity is more important

Efficient large peak leads to instability?

(a) shear viscosity only

(b) with bulk viscosity, larger peak, smaller width

(c) with bulk viscosity, smaller peak, larger width

-decelerate cooling process

b=0fm, Au+Au

J. W. Li, YGM,G.L. Ma, Chin Phys B (2009)

Shear viscosity:

Bulk viscosity:

Relaxation times:

or

2. Central collisions

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Viscous v2 suppression:

-At low transverse momentum, bulk viscosity will result in about 40% additional suppression. This suppression is enhanced at larger impact parameter.

-bulk viscosity can not be neglected especially at large impact parameter.

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difference about bulk-viscous effect on v2

bulk viscosity effects:

(a) Change the flow profile during hydro evolution

(b) Additional spectra correction along freeze-out surface

Song & Heinz: v2 will decrease, flow corrections only (a), , at freeze-out Monnai & Hirano: v2 will increase, spectra corrections only(b), ideal hydro for evolution

ideal hydro visc. hydro:

20%30%

Song & Heinz QM09 talk

Monnai & Hirano QM09 talk

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Heavier Q flow

• Resonance recombination model + Langevin simulation gives good description to spectra and NCQ scaling for phi and J/Psi.

L. Ravagli, H. van Hees,* and R. Rapp, Phys. Rev. C 79, 064902 (2009)

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Charm flow from parton transport model

Ko, Lin et al (AMPT)

Molnar (MPC)

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Single electron v2

• Hirano et.al. can describe RAA but not v2 for single electrons with a relativistic Langevin equation + hydrodynamics. The reason is unclear and it needs further studies.

Yukinao Akamatsu, Tetsuo Hatsuda, and Tetsufumi Hirano, Phys. Rev. C 79, 054907 (2009)

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IV: Summary

• The flow is measured plentifully at RHIC in the past decade, The flow is measured plentifully at RHIC in the past decade,

NCQ scaling studied works in lower energy, smaller system NCQ scaling studied works in lower energy, smaller system

and at forward region. and at forward region.

• The new matter created at RHIC is the most perfect liquid The new matter created at RHIC is the most perfect liquid

known so far, which has a small shear viscosity / entropy known so far, which has a small shear viscosity / entropy

(close to 1/4π).(close to 1/4π).

• When extracting QGP viscosity from experimental data, bulk When extracting QGP viscosity from experimental data, bulk

viscosity effect may not be neglectedviscosity effect may not be neglected

• The hydro-limit is not saturated by the new matter.The hydro-limit is not saturated by the new matter.

• Still a lot needs to be done (both at RHIC and at the LHC)Still a lot needs to be done (both at RHIC and at the LHC)

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V. Outlook

• RHIC detector upgrade will give more precise flow information for identified particles

• Beam energy scan: critical phenomena: non-monotonic behavior, or scaling violation of v2/e

• U+U collision: larger energy density• Thermalization in partonic level?• LHC run

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Barrel TOF-MRPC finished for STAR

run3

run4

run5

One TOFr Tray with 28 prototype MRPC modules installed in STAR

since Oct. 2002

1/2 3/4 5/6 7/8 11/129/10 1/2 3/4 5/6 7/8 11/129/10 1/2 3/4 5/6 7/82006 2007 2008

Prod. Start40 MRPCs

+192 MRPCs+326 MRPCs+326 MRPCs+326 MRPCs

After STAR Construction Readiness Review in April 2006, MRPC mass Production in China started.University of Sci. & Tech. of China (USTC) 1210 (30%*4032) MRPCsOther 70% produced by Tsinghua Univ.

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STAR Collaboration is planning for initial beam energy scan in Run 10 (fall 2009) Primary tool: search for anomalously large particle identified fluctuations with comprehensive particle identification for charged particles provided by TPC + TOFTPC + TOF

Fully China’s TOF complete in time for run 10 (fall 2009)

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Fluctuations and the Critical Point search

Data sample 5k events

• 20 GeV data consistent with systematics observed at SPS

• Rise in fluctuations (K and -h) scale roughly with dN/d across energy and centrality – consistent with NA49

Ready for the Energy scan Critical point searchLarge acceptance means can do a lot with small amount of data

STAR Preliminary

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A good tool looking for phase transition at low energy scan: the breaking of NCQ scaling of elliptic flow

• NCQ scaling for the identified-particle elliptic flow may serve as a probe for searching for critical point.

also see F. Liu’s talk (afternoon)

J. Tian, J. H. Chen, Y. G. Ma et. al., Phys. Rev. C 79, 067901 (2009)

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Searching for Flow collapse and wiggle structure-1st phase Transition H. Stocker

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Energy scan of v1 with AMPTJ.Y. Chen, J. X. Zuo, X. Cai, F. Liu, YGM, A. Tang et al., to be submitted

•AMPT gives larger $v_1$ at low energies than that at high energies, the same trend has been seen in data.

•The values are underestimated;

• The different sign of v_1 between pion and proton at low energies can be understood as nucleon shadowing and baryon stopping;

•when the transverse expansion is strong enough (e.g., at top RHIC energies), it overcomes the ``bounce-off'' motion and causes protons to change its sign of directed flow;

•Hadronic rescattering dose not change much on v1 with the melting version; but large extent with the default version;

•At Low Ebeam, the default result with short rescattering steps looks reasonable

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predicted v2 increase at LHC

• 10% increase in v2 from RHIC to Pb+Pb at LHC is predicted by viscous hydrodynamics.

Matthew Luzum and Paul Romatschke, arXiv:0901.4588

Hirano et al W. Busza

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predicted v2 decrease at LHC

• HYDJET++ Monte-Carlo model predicted a decrease in v2 from RHIC to Pb+Pb at LHC, due to more influential jets at LHC.

G. Eyyubova et. al., arXiv:0907.2190

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V2 from 200GeV/c U+U at RHIC

V2(RP)(U+U) ~ v2(Au+Au)V2(PP)(U+U) ~30-60% larger than Au+Au at the most centrality

Masui,Mohanty,Xu, arxiv:0907.0202

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elliptic flow to measure incomplete equilibration

• Even with 14 mb partonic interaction cross section in AMPT model, it still can not reach the hydro limit. It indicates that the local equilibration of the system is fully not achieved.

J. L. Liu et. al., Phys. Rev. C 79, 064905 (2009)

3 mb

6 mb

10 mb14 mb

Hydro limit

AMPT model with string melting

Au+Au 200 GeV b=8 fm

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Heavy quark azimuthal momentum correlation as a sensitive probe of thermalization

• In high energy collisions of heavy nuclei, frequent interactions among partons of the medium and heavy quarks may lead to important modification of the initially existing correlations.

• On the other hand, hadronic interactiona at the later stage are insufficient to alter azimuthal correlation of DD-bar pairs.

• Hence, a decrease in the correlation strength when compared to pp collisions of heavy quark correlations in high energy collisions of heavy nuclei would indicate early thermalization among partons.

Tsiledaksi et al., arXiv:0908.0427

• A PYTHIA study for p+p at sqrt(s) = 14TeV, a base line:A PYTHIA study for p+p at sqrt(s) = 14TeV, a base line:• Modification or even the complete absence of initial existing correlations in Pb+Pb collisions Modification or even the complete absence of initial existing correlations in Pb+Pb collisions might indicate thermalization at the partonic levelmight indicate thermalization at the partonic level

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Thanks for your attention

Thank Guoliang Ma, Feng Liu et al.!

Thank Workshop organizers!

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V2 behavior can be understood as a thermal nature of produced particles

based on hydrodynamical behavior

V2 is proportional to the beta_T2: upper-left v2 only depend on eccentricity?Tf0: no difference between in-plane & out-of-plane, AuAu & CuCu; Different Npart different Tf0 v2 deps on Tf0

Phenix, arxiv.nucl/0908.0052

rhic 能区的集体流和能量扫描

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