Weekly Report

1
electron / photon flow Elliptic flow
measurement of direct photon in vsNN200GeV
AuAu collisions at RHIC-PHENIX
International Workshop On Hadron Physics and
Property of High Baryon Density Matter
Kentaro MIKI University of Tsukuba
24 Nov 2006
2
0. outline
1. introduction - elliptic flow (hadron,
electron) 2. direct photon analysis - direct
photon analysis as the initial probe of
collisions 3. direct photon v2 - Why do we
analyze the direct photon v2 ? 4. method -
How to measure ? 5. result - The result of
direct photon v2 at PHENIX 6. next step -
internal conversion method 7. summary
3
1-1. initial probe of collisions
Elliptic flow
- the probe of early stage
The collision participation part in the early
stage has spatial anisotropy. Pressure gradient
is largest in the shortest direction of the
ellipsoid. Emission particles reflect initial
spatial anisotropy transfer.
-Elliptic flow (v2) is defined by the 2nd
coefficient of Fourier expansion
2nd harmonic amplitude v2
? azimuthal angle of particles ? azimuthal
angle of reaction plane
fi-?n
4
1-2. particles from collisions
several particles emitted from nuclear collisions
hadron
electron
photon
Elliptic flow were measured at each particles in
PHENIX.
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1-3. Elliptic Flow (hadron)
What have we learned from anisotropic flow of
hadron
v2 scales approximately with the number of
valence quark of hadrons
indicate partonic level flow of ?, K, and proton
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1-4. Elliptic Flow (electron)
What have we learned from Anisotropic Flow of
electron
Electron sources charm decay beauty decay
Dalitz decay Di-electron decay photon
conversion Kaon decay Thermal dileptons
non photonic electron
photonic electron
Compared with quark coalescence model
prediction. consistent with charm quark flow
model below 2 GeV/c.
(1) Consistent with c thermal (2) large cross
section 10 mb
Phys.Lett. B595 202-208
PRC72,024906
indicate charm quark flow
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2-1. Direct photon
Direct photon (non hadronic photon) probe of
initial collision
Photon have much weaker interactions with other
particles and thus preserve information about
their creation.
Direct photons are one of the most
effective probes to study properties of hot dense
medium at initial state of heavy ion collisions.
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2-2. definition of Direct photon
Direct photon all remaining photons after
subtraction of all hadron decay photons
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2-3. Direct photon invariant yield
direct photon invariant yield
Invariant yield of direct photon in PHENIX
thermal window -gt 13 GeV/c (?) prompt
photon -gt 6 GeV/c (?)
Good agreement with Ncoll scaled pQCD.
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2-4. Nuclear modification factor

• Neutral mesons receive strong suppression.
• Direct photon is not suppressed in mid to high pT
• -gt Direct photon have original information
• different from hadron analysis
• Strong suppression of neutral mesons makes
• possible the clear extraction of direct photon
• signal

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3-1. Direct photon v2
motivation !
We attempt to measure the azimuthal anisotropy of
direct photon
two initial probes combine
v2 --- reflect the shape
direct photon --- reflect the properties
of particle emission source
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3-2. Direct photon v2
Direct photon v2 is equal to 0 ? or not ?
prompt photon
v2 0
thermal photon
v2 gt 0
jet fragment photon
v2 gt 0
Thermal photon (HGQGP) v2 R. Chatterjee et al.
nucl-th/0511079
v2 lt 0
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4-1. How to measure hadron decay photon ?
inclusive photon
hadron decay back ground ?0, ?,
direct photon
hadron decay back ground measurement
invariant mass distribution of 2?
hadron decay contamination
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4-2. How to measure direct photon v2 ?
inclusive photon v2
hadron decay back ground v2
direct photon v2

-
(with their weight)
Double ratio
pT GeV/c
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4-3. back ground and inclusive photon
compared hadron decay photon v2 and inclusive
photon v2
centrality 00 to 92 vsNN 200 GeV AuAu
collisions
hadron decay photon v2
inclusive photon v2
subtracted photon (PHENIX preliminary)
subtracted photon (previous analysis result)
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5-1. result direct photon v2
Direct photon v2 estimated by back ground v2
subtracted from inclusive photon v2.
They are the result of direct photon v2 analysis
in AuAu collisions.
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5-2. result direct photon v2
We compared to another v2 analysis and
modification factor.
line total error
PHENIX preliminary

• Direct photon v2 seems to zero within error bar
  in high pT.
• -gt It is consistent to the result of RAA
  analysis.
• - Direct photon v2 may be non zero in 3 to 4
  GeV/c region.
• -gt Thermal photon ??
• Direct photon have smaller v2 than ?0 v2 in high
  pT.
• Direct photon have another value to proton v2 in
  high pT.
• -gt This analysis suggest the another
  information from hadron v2 analysis.

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5-3. result non-photonic electron v2 and RAA
We compared to v2 and RAA at non-photonic
electron.
RAA -gt suppress in the high pT v2 -gt decrease in
the high pT
These figures indicate the another structure to
hadron or photon analysis.
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6-1. Next step
Direct photon v2 need more accuracy to do
discussion as the initial probe of collisions.
- more statistics ? - another method ?
theoretical curve of thermal photon
Thermal photon (HGQGP) v2 R. Chatterjee et al.
nucl-th/0511079
Now, we are interested in internal conversion
method to see the v2 in middle pT.
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6-2. internal conversion method
Any source of real ? produces virtual ? with
very low mass
0-30
90-140
200-300
140-200 MeV
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6-3. invariant yield of direct photon
Direct photon invariant yield is compared to
thermal pQCD curve
L.E.Gordon and W.Vogelsang
Phys. Rev. D48, 3136 (1993)
D. dEnterria, D. Perresounko nucl-th / 0503054
Data consistent with thermal pQCD
If we estimate the direct photon v2 from this
method, is the result improved ?
it continues
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7. summary
Azimuthal Anisotropy of direct photon are
estimated in PHENIX. Direct photon v2 is equal
to zero within error bar in high pT
region. Direct photon v2 maybe have centrality
dependence. In the future, this v2 are measured
at more accuracy in inter-mediate pT. It is
possibility to see the thermal photon effect to
v2. We are determining the internal conversion
method as a next step.
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Ex. Back up
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4-1. RHIC-PHENIX
RHIC The Relativistic Heavy Ion Collider (RHIC)
at Brookhaven National Laboratory is a
world class scientific research facility that
began operation in 2000, following 10 years of
development and construction.
lead scintillator (PbSc) energy resolution
2.1 ? 8.1 / E1/2 GeV
lead glass (PbGl) energy resolution 0.76 ?
5.95 / E1/2 GeV
? lt 0.375 ??90??2
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Ex. result subtracted photon
PHENIX preliminary
PHENIX preliminary
PHENIX preliminary
PHENIX preliminary
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Ex. result direct photon v2
PHENIX preliminary
PHENIX preliminary
PHENIX preliminary
PHENIX preliminary