Transcript Elliptic Flow in PHENIX

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 ?
• Study the properties of
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
Z
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
Y
X
Py
Pz
– Elliptic flow (v2) is defined by the
2nd coefficient of Fourier expansion
Px
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Outline
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
partonic
direct
D
hadronic

, K, p
time
Elliptic Flow, v2
Partonic degrees of freedom, Thermalization, ..
Elliptic Flow, v2
 Meson
• Bulk, early probe
• Charged hadrons
give us a base line
Penetrating probes
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• Small interaction cross section,
long lived life time (~40 fm/c)
• Heavy flavor electrons (charm)
• Direct 
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Baseline : charged hadrons
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
PHENIX : PRL 91, 182301 (2003)
Charged hadrons, v2 vs
pT
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
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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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CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
1.  meson v2
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Clear  signal
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
•  reconstruction
via K+K- decay
channel
Before subtraction
Signal + Background
Background
After subtraction
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– 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.
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“Meson” type flow !
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
 v2 vs pT
• Hydro. mass ordering for pT < 2 GeV/c
• v2() ~ v2(), v2(K) for pT > 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
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
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
WWND 2006, M. Issah
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Partonic degrees of
freedom
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CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
2. Heavy flavor
electron v2
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Clean heavy flavor electron
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
Cocktail subtraction
Converter subtraction
Signal / Background ratio
Run4
Run2
• Two different techniques show an
excess heavy flavor electron signal
– Signal/Background > 1 for pT > 1 GeV/c
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Hint of Charm flow
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
V. Greco, C. M. Ko, R. Rapp: PL B 595,
202 (2004)
e v2 vs pT
• 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
input
v2
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
H. Hees, V. Greco, R. Rapp: PRC 73,
034913 (2006)
output
(1) D or B meson v2
(2)
(1) decrease, (2) flat at high pT
De
B  e (1)
B  e (2)
Simulation
SQM 2006, S. Sakai
pT (GeV/c)
• High pT drop might be explained
by B meson contribution
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CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
3. Direct  v2
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Clear Direct  signal
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
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
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
PRL 96, 032302 (2006)
• Direct  v2
1. Hard scattering
• v2 = 0
• Inclusive 
– Consistent with expected 
v2 from hadron decays
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2. Parton
fragmentation
• v2 > 0
3. Bremsstrahlung
• v2 < 0
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v2direct = 0 ?
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
PRL 96, 032302 (2006)
 v2 vs pT
• 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
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
• Elliptic Flow is powerful tool to study hot and
dense matter at RHIC
•  meson  Partonic degrees of freedom
– Hydro. mass ordering for pT < 2 GeV/c
– For pT > 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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CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
Thank you
Hiroshi Masui / University of Tsukuba
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CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
Back up
Hiroshi Masui / University of Tsukuba
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Converter Subtraction method
Ne
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
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     e+e• 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
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
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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CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
Inclusive & photonic electron v2
• Photonic
photonic e v2
inclusive e v2 (w/o. converter)
electron v2
– pT < 1 GeV/c
 Converter method
– pT > 1 GeV/c
Simulation
– v2(inclusive) < v2
(photonic)
 v2(non-photonic) <
v2(photonic)
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CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
Centrality dependence
• Non zero heavy flavor electron v2 !
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CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
Run4 inclusive  v2
v2
0
inclusive 
pT
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Independent on system size
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
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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CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
Hadron identification
• Time-of-flight
• EM Calorimeter
– || < /4, || < 0.35
– Timing resolution ~ 120 ps
– || < /2, || < 0.35
– Timing resolution ~ 400 ps
• /K separation ~ 2 GeV/c
• K/p separation ~ 4 GeV/c
• /K separation ~ 1 GeV/c
• K/p separation ~ 2 GeV/c
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The PHENIX experiment
• Acceptance
CIPANP 2006, Westin Rio Mar Beach, Puerto Rico, May 30 – Jun 3, 2006
– Central arm: || < , || <
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
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