mass, quark-number, energy dependence of v 2 and v 4 in relativistic nucleus- nucleus collisions yan...

Mass, Quark-number, Energy Dependence of v2 and v4 in Relativistic Nucleus-Nucleus

Collisions

Yan Lu University of Science and Technology of China

Many thanks to the organizers.

吕第 10 届粒子物理大会 , 南京 , April 26-29, 2008 2

publication

Phys. Rev. C 75, 054906 (2007)

One of principle authors for STAR collaboration

Most of work done as Ph.D student in CCNU.


Outline

Introduction and Motivation

Experiments

Results and Discussions

Summary


Goal of Heavy Ion Collision

QGP is taken to be a (locally) thermalized state of matter in which quarks and gluons are deconfined, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic volumes.

RHIC white papers - 2005, Nucl. Phys. A757, STAR: p102; PHENIX: p184.

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

Time

Initial conditions

Initial hard interactions

Hot and dense matter

Hadronization and chemical freeze-out

Kinetic freeze-out


QGP signature: collective flow

In high-energy nuclear collisions, interaction among constituents and density distribution will lead to: pressure gradient pressure gradient collective flow collective flow Pressure gradient only depends on the density gradient and interactions

...])φ[2cos(2φcos211

212

2

3

3

RRT

vvdydp

Nd

pd

NdE

Experiments: Fourier expansion of the azimuthal pT distribution

])φ[2cos(2 Rv ])φ[4cos(4 Rv

Reaction plane azimuthal angelImportant flow parameters:

x

z

Non-central CollisionsReaction plane: x-z plane


y

x

py

px

coordinate-space-anisotropy momentum-space-anisotropy

Elliptic flow v2

y2 x 2

y 2 x 2v2 cos2 , tan 1(

pypx

)

Azimuthal anisotropy of density gradient. Interactions anisotropy in momentum space. Self-quench: elliptic flow is sensitive to the early stage.


Results at RHIC

Phys. Rev. Lett. 91, 092301, 2003; Nucl. Phys. A 757, 102, 2005, p38

At low pT, the heavier hadron, the smaller v2 – mass ordering. At intermediate pT, v2 depends on number of constituent quark – nq-scaling.

Partonic collectivity and de-confinement at RHIC.


Motivation

- Gain information on interplay of collectivity, NQ scaling as a function of collision centrality and energy.

- Determine parameters for partonic EoS.

Collectivity Energy dependence nq-scaling


STAR detector

Acceptance: full azimuthal coverage; pseudo-rapidity coverage || < 1 Advantage for event-wise correlations.


Particle Identification I

TPC dE/dx PID: pion/kaon: pT ~ 0.6 GeV/c; proton pT ~ 1.2 GeV/c TOF PID: pion/kaon: pT ~ 1.8 GeV/c; proton pT ~ 3 GeV/c


Particle Identification II

0S

() p (p ) )()( )()(

PID extends to high pT.


Event Plane Method Estimation of the true reaction plane using elliptic flow itself. - flow vector

where sum over all particles. - event plane angle

v2 calculation

2/tan2

212

x

y

Q

Q

i

iixQ )2cos(2

i

iiyQ )2sin(2

22 2cos obsv

EPobs resvv /22

A. M. Poskanzer, S. A. Voloshin, Phys. Rev. C58, 1671 (1998)

Flat distribution.


62.4 GeV Au+Au results

0-80% minimum bias. Omega, lack of hadronic interaction consistent with mass-ordering. Achievement of partonic collectivity in 62.4 GeV Au+Au.


Number-of-Quark Scaling

Number-of-Quark Scaling is observed in 62.4 GeV Au+Au. Better scaling in transverse kinetic energy scale.

Kinetic energy: mT – m0 = (pT)2 + m02 - m0


Centrality Dependence

v2 is larger in more peripheral collisions due to larger . mass-ordering is observed for all centrality intervals.


More Central, stronger flow

Divide to remove initial geometry effect.

At a given centrality, v2 follows Number-of-Quark Scaling.

v2/ is larger in more central collisions, indicating stronger flow in more central collisions.


v4

v4 scale with 1.2 (v2)2 ~ (nq)2 for meson and baryon.

v4 tested the constituent quark degree freedom to higher order.


Energy Dependence

Similar v2 for 62.4 and 200 GeV.

10-15% smaller at SPS than at RHIC.

Onset of limiting behavior toward RHIC energy.


Summary

We report azimuthal anisotropy parameter v2 of , , p, , , from Au+Au collisions at 62.4 GeV. 0%-10%, 10%-40% and 40%-80% centrality bins are presented.

At low pT, mass-ordering is observed.

At intermediate pT, Number-of-Constituent-Quark scaling is observed.

Stronger flow is observed in more central collisions.

Magnitude of v2 is similar for 62.4 GeV and 200 GeV, 10-15% higher than17.3 GeV at SPS.


Thanks!


QCD phase diagram

Baryon Density


Analysis Method: v2 vs. minv

V0 reconstruction

KS0

() p (p )

68.95%

63.9%

v2 vs. minv Method

assume

Robustness:Away-peak points constrainNear-peak points constrain

Borghini et al. Phys. Rev. C70 (2004) 064905

)()()(

)()(2cos()(

22

2

invinvBg

invSig

invrinvBgSig

mBgSig

Bgmvm

BgSig

Sigv

mmv

bmamv invinvBg )(2

Bgv2Sigv2


y

x

py

px

coordinate-space-anisotropy momentum-space-anisotropy

Anisotropy Parameter v2

y2 x 2

y 2 x 2v2 cos2 , tan 1(

pypx

)

Initial/final conditions, EoS, degrees of freedom


Goal of Heavy Ion Collision

QGP is taken to be a (locally) thermalized state of matter in which quarks and gluons are deconfined, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic volumes.

RHIC white papers - 2005, Nucl. Phys. A757, STAR: p102; PHENIX: p184.

PCM & clust. hadronization

NFD

NFD & hadronic TM

PCM & hadronic TM

CYM & LGT

string & hadronic TM

Time

Initial conditions

Initial hard interactions

Partonic matter — QGP

Hadronization and chemical freeze-out

Kinetic freeze-out


Relativistic Heavy Ion Collider

RHIC BRAHMSPHOBOS

PHENIXSTAR

AGS

TANDEMS

v = 0.99995c = 186,000 miles/sec Au + Au at 200 GeV

Brookhaven National Laboratory (BNL), Upton, NYBrookhaven National Laboratory (BNL), Upton, NY


Collision Geometry

x

z

Non-central Collisions

Au + Au sNN = 200 GeV

Uncorrected

Charge particle multiplicity collision centralityReaction plane: x-z plane

mass, quark-number, energy dependence of v 2 and v 4 in relativistic nucleus- nucleus collisions yan...

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