Measurement of Azimuthal Anisotropy
with the New Reaction Plane Detector
in the PHENIX experiment

Yoshimasa Ikeda
for the PHENIX collaboration(University of Tsukuba)Azimuthal anisotropy
Spatial anisotropy in noncentral collision provides
azimuthal anisotropy ofparticle emission.
The large anisotropy is anevidence of the formation ofa hot and dense partonicmatter.

dN∝12 v 2 cos 2Φ−Ψ dΦΨ : reaction plane angle2

Motivation of v2 measurement
Large v2 was observedin RHICThe values agreed withhydro-dynamical models
It suggests rapid
thermalization andquark flow.

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KET and quark number scaling
PHENIX. PRL. 99, 052301 (2007)●●●The values of v2 arein proportion to thenumber of quarks
heavy particle shifts
to high pT
These agree very wellby KET/nq scaling at
low pT range.

KET =  M 2−PT2 −M4

Reaction Plane Resolution

cos2ΔΨ

●Reaction plane
resolution was ~0.4
before the introductionof the reaction plane
detector.
– The observed v2v 2 observe=v 2 real×〈cos2  real−observe 〉11
 v 2~×〈cos 2 real−observe 〉  N

strength is only
less than 40% of
its real value.

– statistical power lessthan 1/6.

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Reaction Plane Detector (RxP)
The reaction plane detector wasinstalled just before Run7 (2007).

35cm

Collision piont

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Acceptance of “RxP”
PHOBOS, PRL. 91, 052303 (2003) RxP measure more particles

and the particles with morelarge v2.
RxP : η = ±1~2.8(blue)
BBC : η = ±3.1~4(red)7New Reaction Plane ResolutionRxPv2 plane|η| = 1.0 – 2.8 New!

RxPinner |η| = 1.5 – 2.8 New!
RxPouter |η| = 1.0 – 1.5 New!
MPC|η| = 3.0 – 4.0 New!

BBC|η| = 3.1 – 3.9

CNT|η| = 0 – 0.35

SMD|η| > 6v 2 observe=v 2real×〈cos 2real−observe 〉11
 v 2~×〈 cos 2  real− observe 〉 N

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PID in PHENIX
πKp

TOF.W
pT = 1 – 2 GeV

dm2 [GeV2]

EMC + TOF.E
Proton-π continuum

Mean of the peak
1.11463±0.00004
Mass of lambda(PDG)
1.11568±0.000006
9Invariant mass [GeV]v2 before and after
PHENIX. PRL. 99, 052301 (2007)

Centrality
20-60%

Before (Run4)

After (Run7)

BBC RP resolution (< 0.4)
0.8 billion events

Better resolution of RxP (< 0.75)
Higher statistical (3.5 billion) 10

Number scaling by quark or atom
d2p2

dTp
Tv ~2 v , p ~2 p●●●

Deuteron and proton
are consistent almoston the number scaling.
It is agree that the pand n have same v2
and final state
coalescence of them.
Deuteron peak is
expected at pT=6GeV/c.
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KET scaling●●●

KET =  M −PT −M22

They are consistentbetween mesons orbaryons.
The values are
decided by centrality,KET and quark
number.
Meson line andbaryon line approachat high KET.
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Quark number and KET scaling●●●

Consistent for allparticles on KET andquark number scalingat KET/nq<0.8GeV.
They approach at highpT. (deviate on KET/nqscaling)
This indicate a changeof particle and v2
production mechanism.
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Heavy flavor and J/ψ v2(Run4)(Run7)●●●(Run7)The data at low pT favor
the models that include
quark level elliptic flow ofcharm.
It could not be judged
whether J/Psi succeeds
the charm flow Because
the poor statistics.
B meson decay becomesa significant source
above 2.5 GeV/c.
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Summary●The new reaction plane detector worked well.
– Resolution is improved by a factor of two.
– It means 4 times of statistic Power.

●Deuteron v2 and pT are double of proton.

d2dTp
2p
Tv ~2 v
p ~2 p– d and p are consistent on atom number scaling.
– It agree the p-n coalescence in final state.
●v2 is decided by centrality, KET and nq on KET scaling.
– Consistent for all particles on KET and nq scaling at

KET<0.8GeV.

●v2 have no depend on particles at high pT range.
– Production

mechanism is different.

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Back up

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Reaction Plane Detector (RxP)
The reaction plane detector was
installed just before Run7 (2007).

35cm

Collision piont

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Correlation effectv2 is over estimated bycorrelation effect.
According to
HIJING+PYTHIA, the effectby jet does not have any
problem with η>1.5

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Design and Geant simulation
resolution

Detector parameters
were optimized with
Geant simulation
ThicknessScintillator 2cm
Converter 2cm
Φ division

Φ division into 1221

π0 → 2γ (98.8%) cτ=25.1[nm]22Configuration of RxP23