John C.-H. Chen 1

vn in PHENIX

John Chin-Hao ChenRIKEN Brookhaven Research Center

INT Ridge Workshop2012/05/08

John C.-H. Chen 2

vn: particle anisotropy• The colliding area is

“almond” like shape due to overlap of two colliding nuclei.

• The particle angular distribution: dN/d(-) =N0((1+2vncosn(-)))

• v2 = elliptic flow

John C.-H. Chen 3

Many information coming from flow

• Equation of State (EOS)• shear viscosity (η),• specific viscosity (η/s) of

sQGP • and their temperature

dependence

• Key to understand the QGP!

John C.-H. Chen 4

Fluctuation matters

• Nucleon distribution is not smooth, or initial state fluctuation -> finite vodd

• Azimuthal symmetry of the colliding area no longer available

• vodd is possible• We can “measure”

the fluctuations directly

John C.-H. Chen 5

v3, reason for ridge and shoulder?

• Ridge sits at ~ 0, shoulder sits at ~2/3, 4/3– A 3-peak structure!

• v3 (Fourier Coefficient of the cos3term) gives a natural 3-peak structure

• Is v3 the explanation?

John C.-H. Chen 6

How do we measure vn?

• Reaction plane method– Use forward detector to determine the n-th

reaction plane, n

– dN/d 1+2vncos n(-n)– vn = <cos n(-n)>

• Two particle correlation method– central-central or central-forward correlation– dNpair/d 1+(2vn

AvnBcosn)

John C.-H. Chen 7

John C.-H. Chen 8

Reaction plane method

• vn {n} = <cos(n(-nave))> / Res(n)

• nave is the average of the raw reaction

plane between north and south sub-events

• Res(n) is the reaction plane resolution

John C.-H. Chen 9

Correlation factor

• Res(n), Resolution of reaction plane measures cosine of dispersion of estimator () from truth

• Res(2) = <cos(2(2(N/S) – RP))>

= sqrt(<cos2(2N – 2

S)>)

• Key Quantity: cosine of dispersion (Raw vn of A wrt B)– <cos j (m

N – nS)>

John C.-H. Chen 10

Reaction plane correlation (i)

• <cos j (mA – n

B)>

• N-th reaction plane (n) correlates across large rapidity (|A-B|~5, |C-D|~7)

• N = 1 (1) has negative correlation due to conservation of momentum

PRL 107 252301 (2011)

A: RXN North [1.0-2.8] B: BBC South [3.1-3.9] C: MPC North [3.1-3.7]D: MPC South [3.1-3.7]

John C.-H. Chen 11

Reaction plane correlation (II)

• 2 correlates with 1

• 2 correlates with 4

• 2 does not correlate with 3

• 1 correlates negatively with 3, – some intrinsic v3 not coming from fluctuation?

PRL 107 252301 (2011)

A: RXN North [1.0-2.8] B: BBC South [3.1-3.9] C: MPC North [3.1-3.7]D: MPC South [3.1-3.7]

John C.-H. Chen 12

vn(n) vs pT

• All vn increases with pT

• v3 is independent from centrality

PRL 107 252301 (2011)

John C.-H. Chen 13

Characterize the initial state anisotropy

• Glauber initial state condition

• use n to measure the initial state anisotropy

John C.-H. Chen 14

vn vs n

• vn follows the trend of n

• Initial state anisotropy translate to final state momentum anisotropy

John C.-H. Chen 15

v3(2p) vs v3(3)

• v3 measured by two particle correlation method (0.3<||<0.7) is consistent with, but slightly higher than the reaction plane method

• Contributions from non-flow (jet contribution) in this range

John C.-H. Chen 16

vn vs theory

• All theory predicts v2 well

• v3 adds in additional discrimination power

• Data favors Glauber + /s = 1/4

PRL 107 252301 (2011)

John C.-H. Chen 17

Jet shape with higher vn modulated background subtraction

• When v3 modulation is included, the double peak structure in away-side disappears.

200GeV Au+Au0-20%, inc. -had.

John C.-H. Chen 18

v2 of Identified particles

• v2 of identified particles are measured

• (v2/nq) are the same for all particles– Flow exists at partonic level

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High pT PID v2

• new detector TOFw and Aerogel enhance PID capability• Dedicated reaction plane detector• Extend to high pT

arxiv:1203.2644

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NQS breaks?

• NQS holds at 0-20%• Obviously breaks at 20-60% at KET/nq > 1.0 GeV

arxiv:1203.2644

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KET/nq scaling vs centrality

• With finer centrality bins, the centrality dependence is clear

• KET/nq scaling works at 0-10%

• It starts breaking at 10-20% at KET/nq~ 1.0 GeV

Arxiv:1203.2644

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PID v3 @ 200 GeV Au+Au

• Mass ordering at low pT

• Baryon/meson splitting at intermediate pT

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NQS of PID v3

• Similar (v3/nq) scaling exists in v3

• v3 also shown in partonic level

John C.-H. Chen 24

QCD phase transition

• QGP is created at RHIC at 200 GeV

• RHIC is flexible in beam energy– Down to 7.7 GeV

• Can we find the critical point?– Any significant

feature?

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vn{n} at 39 GeV

• Inclusive charged hadrons• Significant values of v3 and v4

• Trend similar to vn at 200 GeV

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Beam energy dependence of vn

• Various beam energy: 39, 62, 200 GeV• No significant beam energy dependence• Hydro dynamical behavior down to 39 GeV

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PID v2 @ 62.4 and 39 GeV

• NQS scaling still works at 39 GeV!

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v2 measurement in broad energy range

• At 7.7 GeV, the v2 value is significantly lower than 200 GeV

• A possible transition between 7.7 and 39 GeV?

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Saturation function of vn

• Not only v2 is saturated, but also the v3 and v4, starting from 39 GeV

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summary

• vn has been measured systematically in PHENIX

• vn is independent from beam energy between 39 GeV to 200 GeV

• KET/nq scaling work on PID v2 from 39-200 GeV

• But the KET/nq scaling breaks at large KET/nq in mid-central collisions