Elliptic Flow in PHENIX

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Elliptic Flow in PHENIX

• Hiroshi Masui
• for the PHENIX collaboration
• CIPANP 2006, Westin Rio Mar Beach
• Puerto Rico
• May 30 Jun 3, 2006

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Why Elliptic Flow ?
Z

• Study the properties of matter created at RHIC
• The probe for early time
• The dense nuclear overlap is ellipsoid at the
  beginning of heavy ion collisions
• Pressure gradient is largest in the shortest
  direction of the ellipsoid
• Spatial anisotropy ? Momentum anisotropy
• Signal is self-quenching with time
• Elliptic flow (v2) is defined by the 2nd
  coefficient of Fourier expansion

Reaction plane
Y
X
Pz
Py
Px
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Outline
partonic
hadronic
?
direct?
Elliptic Flow, v2
time
D
?, K, p
Partonic degrees of freedom, Thermalization, ..

• Elliptic Flow, v2
• Bulk, early probe
• Charged hadrons
• give us a base line

• ? Meson
• Small interaction cross section, long lived life
  time (40 fm/c)
• Penetrating probes
• Heavy flavor electrons (charm)
• Direct ?

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Baseline charged hadrons
Charged hadrons, v2 vs pT
PHENIX PRL 91, 182301 (2003)
v2 k ? ?

• Large elliptic flow at RHIC
• Consistent with hydrodynamics with rapid
  thermalization, ? 1 fm/c
• v2 scales initial eccentricity (?) of reaction
  zone

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Hydro scaling
M. Issah, A. Taranenko, nucl-ex/0604011
Hydro scaling of v2
K0S, ? (STAR) PRL 92, 052302 (2004) ? (STAR)
PRL 95, 122301 (2005) ?, K, p (PHENIX)
preliminary
Meson v2
Baryon v2
KET mT m0 at y 0

• Scaling holds up to KET 1 GeV
• Meson/Baryon v2
• Possible hint of partonic degrees of freedom

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1. ? meson v2
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Clear ? signal

• ? reconstruction via KK- decay channel
• S/N 0.3
• Centrality 20 60
• S/N is good
• Event plane resolution is good
• Separation between meson/baryon v2 is good
• v2 do not be varied too much.

Before subtraction
Signal Background
Background
After subtraction
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Meson type flow !
? v2 vs pT

• Hydro. mass ordering for pT lt 2 GeV/c
• v2(?) v2(?), v2(K) for pT gt 2 GeV/c
• Mass Number of constituent quarks
• Consistent with the description by quark
  coalescence, recombination models

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Hint of partonic d.o.f
Hydro scaling of v2
K0S, ? (STAR) PR 92, 052302 (2004) ? (STAR)
PRL 95, 122301 (2005) ? (STAR) preliminary ?,
K, p, ?0, d (PHENIX) preliminary

• Hydro Nquark scaling
• Works for a broad range of KET
• ? meson also follow the scaling
• Partonic degrees of
• freedom

WWND 2006, M. Issah
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2. Heavy flavor electron v2
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Clean heavy flavor electron
Cocktail subtraction
Converter subtraction
Signal / Background ratio
Run4
Run2

• Two different techniques show an excess heavy
  flavor electron signal
• Signal/Background gt 1 for pT gt 1 GeV/c

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Hint of Charm flow
e v2 vs pT
V. Greco, C. M. Ko, R. Rapp PL B 595, 202 (2004)

• Data indicate finite v2 of charm quark
• Suggest thermalization of c quark as well as
  light quarks
• What is the origin of high pT drop ?

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b quark contribution ?
e v2 vs pT
H. Hees, V. Greco, R. Rapp PRC 73, 034913 (2006)
(1)

• D or B meson v2
• decrease, (2) flat at high pT

input
(2)
v2
D ? e
output
B ? e (1)
Simulation
B ? e (2)
SQM 2006, S. Sakai
pT (GeV/c)

• High pT drop might be explained by B meson
  contribution

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3. Direct ? v2
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Clear Direct ? signal
PRL 94, 232301 (2005)

• Large direct ? excess
• ?0 is suppressed but direct ? not
• Both results are consistent with pQCD

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Possible 3 different scenarios
? v2 vs pT
PRL 96, 032302 (2006)

• Direct ? v2
• 1. Hard scattering
• v2 0
• 2. Parton fragmentation
• v2 gt 0
• 3. Bremsstrahlung
• v2 lt 0

• Inclusive ?
• Consistent with expected ? v2 from hadron decays

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v2direct? 0 ?
? v2 vs pT
PRL 96, 032302 (2006)

• Direct ? v2
• Direct ? excess ratio is consistent with
  v2BG/v2inclusive?, suggest v2direct? 0
• Favors prompt photon production for dominant
  source of direct ?

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Conclusions

• Elliptic Flow is powerful tool to study hot and
  dense matter at RHIC
• ? meson ? Partonic degrees of freedom
• Hydro. mass ordering for pT lt 2 GeV/c
• For pT gt 2 GeV/c, v2(?) prefer quark composition
  not mass
• Hydro Nquark scaling works for ? meson as well
  as other hadrons
• Heavy flavor electron ? Thermalization
• Consistent with non-zero charm flow, suggest
  thermalization of c quark as well as light quarks
• Bottom contribution at high pT need to be studied
  experimentally
• Direct ? ? Coming soon
• v2direct? 0, consistent with the scenario of
  direct ? production from initial hard scattering
• Year-4 data may enable us to reduce statistical
  error bars, and extend pT reach, and to measure
  thermal ? v2

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Thank you
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Back up
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Converter Subtraction method
Ne
0.8
1.1
?
1.7
With converter
Photonic electron
W/o converter
Photon Converter (Brass 1.7 X0) around beam
pipe
Conversion from beam pipe
Dalitz 0.8 X0 equivalent
Non-photonic electron
0
X0

• Source of background electrons
• Photon conversion ?0 ? ? ? ? ee-
• Dalitz decay (?0 ?ee?, ? ?ee?, etc)
• Di-electron decays of ?, ?, ?
• Kaon decays
• Conversion of direct photons

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Inclusive electron v2 (w., w/o. converter)

• Converter subtraction method
• Inclusive electron v2 w. and w/o. converter.
• Clear difference between them.
• Electron v2 with converter include large photonic
  component.

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Inclusive photonic electron v2

• Photonic electron v2
• pT lt 1 GeV/c
• ? Converter method
• pT gt 1 GeV/c
• Simulation
• v2(inclusive) lt v2 (photonic)
• ? v2(non-photonic) lt v2(photonic)

photonic e v2
inclusive e v2 (w/o. converter)
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Centrality dependence

• Non zero heavy flavor electron v2 !

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Run4 inclusive ? v2
?0
v2
inclusive ?
pT
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Independent on system size
Eccentricity scaling

• Eccentricity scaling
• A wide range of centrality
• Independent of system size
• Integrated v2 ? eccentricity
• Reduce systematic error from eccentricity
  calculation
• Cancel systematic error by the ratio of v2(pT) /
  (integrated v2)

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Hadron identification

• Time-of-flight
• ? lt ?/4, ? lt 0.35
• Timing resolution 120 ps
• ?/K separation 2 GeV/c
• K/p separation 4 GeV/c

• EM Calorimeter
• ? lt ?/2, ? lt 0.35
• Timing resolution 400 ps
• ?/K separation 1 GeV/c
• K/p separation 2 GeV/c

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The PHENIX experiment

• Acceptance
• Central arm ?? lt ?, ?? lt 0.35
• Centrality
• Beam-Beam Counter, Zero Degree Calorimeter.
• Event plane
• BBC
• Tracking
• Drift chamber, Pad chambers.
• Particle identification
• Electron
• Electro-Magnetic Calorimeter
• Hadron
• Time-of-Flight, Aerogel Cherenkov Counter, EMCal