1. Elliptic flow of electrons/positrons in 200 GeV Au+Au collisions at RHIC-PHENIX
坂井　真吾　for the PHENIX Collaboration
Shingo Sakai
　 Univ. of Tsukuba
for the PHENIX Collaboration

2. Motivation(1) Clear excess about 1 GeV/c with respect
Page 1
g conversion
p0  gee
h  gee, 3p0
w  ee, p0ee
f  ee, hee
r  ee
h’  gee
From Run1 result
(PHENIX: PRL 88(2002)192303)
Electron source
Dalitz decays
Di-electron decays
Photon conversions
Kaon decays
Thermal dileptons
charm decay
beauty decay
Inc.e/pho.e
Electron sorce
From Rnn1 resul
Consiten
Photonic
Above 1 GeV/c charm decay contribution is large
high pt electron v2 can carry information about the anisotropy of the parent charmed mesons
PYTHIA
Inc.e/pho.e
High pt energy loss ?
Clear excess about 1 GeV/c with respect
to photon conversion and light hadron
decay.

3. Motivation(2) The photonic-subtracted electron
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direct g
(J. Alam et al. PRC 63(2001)021901) b c
The photonic-subtracted electron
single spectra consistent with charm
decay (binary scaled).
“The high pt electron v2 can carry
information about the anisotropy
of the parent charmed mesons. “
PYTHIA
Electron sorce
From Rnn1 resul
Consiten
Photonic
Above 1 GeV/c charm decay contribution is large
high pt electron v2 can carry information about the anisotropy of the parent charmed mesons
PYTHIA
High pt energy loss ?
photonic-subtracted
electron

4. Measurement of v2e dN/d(-) = N (1 + 2v2obscos(2(-))) e - Page 3
<<Reaction Plane Method>>
Measure azimuthal angle of each particle
with respect to the reaction plane Y
dN/d(-) = N (1 + 2v2obscos(2(-))) X
Reaction
Plane
 : azimuthal angle of reaction plane
: azimuthal angle of electrons
v2obs: strength of azimuthal anisotropy
(fitting of dn/d(-) or v2=<cos2(-)>)
v2 = v2obs/ σ e
- e
r.p
 wi*sin(2i)
tan2  rp =
 wi*cos(2i)
σ=<cos(2(m-real))>
= {<cos(2(A-B))>}1/2

5. Electron measurement at PHENIX
Page 4
Electron measurement at PHENIX
The PHENIX experiment has the unique capability to measure
electrons at RHIC
Electron identification :
Cherenkov light in RICH
- |h|  0.35
- pt 0.2~4.9 GeV/c
Number of hit PMT
Ring shape
Geometry of PMT
-installed North and South side of RHIC.
-3 unit rapidity away from mad rapidity
Electron identification

6. Reaction plane Determine r.p using BBC north and south Page 5
Correlation r.p BBC_north & r.p BBC_south
r.p resolution
<cos(2(A-real))>
= {<cos(2(A-B))>}1/2
v2 =v2 obs / resolution
Correlation r.p BBC_north & r.p BBC_south
Centraryty
Determine r.p using BBC
central
central
peripheral
Centrality [%]

7. dn/d distribution Page 6 v2e is corrected by
subtracting miss ID of electrons
e+(e-)
candidate
Miss ID e+(e-)
-p/2 p/2
cand --- dn/dphi of candidate
(detected RICH)
e+(e-)
miss ID --- dn/dphi of miss ID
(dn/d)/N0
1.5
V2e is estimated by subtracting miss ID of electrons
1.0
1.0
dn/d of after
subtract Miss ID
e+(e-)
0.5
-p/2 p/2 pt
1.0
2.0
3.0
4.0

8. Pt dependence of v2(e) Page 7 v2 (M.B) pt[GeV/c] Systematic error R.P
method
(fitting / <cos2()>)
electron ID
V2e
Simulation
Photon conversion & Dalitz decay from pi0
It seem like that v2e originating from pi0 is not consistent with v2e which is including all electron sources
Electron source
Systematic error
R.P
method (fitting / <cos2()>)
electron ID
(M.B)
pt[GeV/c]

9. Comparison with v2 of hadrons
Page 8 v2
<<Low pt (pt<1.0GeV/c)>>
v2(e) is larger than v2(pion)& v2 (proton)
-> dominant pi0 decay
- small decay angle
- decay from higher pt
v2 pion & v2 proton :
nucl-ex/ (PHENIX)
v2 (proton)
v2 (pion)
v2(e)
<<High pt (pt>2.0GeV/c)>>
v2(e) seems like smaller than v2 (pion)
Particular interest because of the contributions from heavy flavor
(M.B)
particular interest because of the
contributions from heavy-quark
(c/b) decays !(but the data include another sources now)
(M.B)
pt[GeV/c]

10. What is needed to estimate charmed electron v2 ?
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What is needed to estimate charmed electron v2 ?
Relative charm yield to the inclusive electron yield at Run2 (r= Np/Ne)
electrons v2 originating photonic source
Study v2 D->eX (due to large Q value)
R=Nc/Ne

11. Summary
Page10
Azumithal anisotropy of inclusive electrons/positrons are measured with respect to the reaction plane in 200 GeV Au+Au collision at RHIC-PHENIX.
v2(e) is larger than v2 (pion) & v2 (proton) at low pt.
v2(e) seems like smaller than v2 (pion) at high pt
Next Run (Au+Au) will start soon.
much more statistics (error bars will be much smaller)