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Electron and identified hadron v2
to look for hadronic or partonic
origin of elliptic flow
Shingo Sakai
for the PHENIX Collaboration
Univ. of Tsukuba
page1
Outline



Introduction
- motivation
- method
- overview of PHENIX detctor
Hadron v2 (/K/p/d)
- comparison with hydro model
- quark coalescence model (nquark scaled v2)
Electron v2
- comparison with hadron v2
Introduction
page2
Why identified v2 ?
ｙ
The azimuthal anisotropy of particle
emission reflects
-> Low pt
- pressure gradient of early stage
of collision
- hydrodynamical behavior
-> High pt
- parton energy loss in hot &
dense medium
Measurement of identified particle v2
gives us much more information of the
collision dynamics
ｘ
Initial spatial anisotropy
pｙ
p
ｘ
Momentum space anisotropy
of particle emission
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Measurement of v2
<<Reaction Plane Method>>
Measure azimuthal angle of each particle
with respect to the reaction plane
Y
dN/d(-) = N (1 + 2v2obscos(2(-)))
 : azimuthal angle of reaction plane

: azimuthal angle of particle
v2obs: strength of azimuthal anisotropy
(fitting of dn/d(-) or v2=<cos2(-)>)
v2 = v2obs/ σ
tan2  rp =
 wi*sin(2i)
 wi*cos(2i)
σ=<cos(2(m-real))>
= {<cos(2(A-B))>}1/2
X
Reaction
Plane
e
-
r.p
Over view of PHENIX detector
Charged Particle Tracking:
Drift Chamber
Pad Chamber
Time Expansion Chamber
Particle ID:
Time of Flight
Ring Imaging Cerenkov Counter
TEC
Muon ID (PDT’s)
Calorimetry:
Pb Scintillator
Pb Glass
Event Characterization
Beam-Beam Counter
Zero Degree Calorimeter
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hadron v2
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Hadron measurement @ PHENIX
The PHENIX experiment has the high
timing resolution TOF counter.
- TOF ~ 115 ps
– : 0.2 < pT < 3.0 GeV/c
–K : 0.4 < pT < 3.0 GeV/c
–P : 0.6 < pT < 4.0 GeV/c
Phenix (East-Arm)
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Particle ID
PID : m2 = p2 {(TOF/L)2 -1}
Momentum [GeV/c]
d
π
K P
mass2 [(GeV/c2)2]
Clear signal peaks
mass2 [(GeV/c2)2]
Reaction plane
Page 7
Determine r.p using BBC north and south
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
central
peripheral
Centrality [%]
Comparison with hydro model
• pT < 2.0 GeV/c
– Clear mass dependence
v2() > v2(K) > v2(p)
Consistent with hydrodynamical
model.
• pT > 2.0 GeV/c
– v2(p) > v2()
– Clear departure from
hydrodynamical behavior is
observed.
– Saturation at intermediate pT.
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Quark coalescence model
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nucl-ex/0305013 (PHENIX)
Quark coalescence model
v 2,M (p T )  2v 2,q (p T /2)
v 2,B (p T )  3v 2,q (p T /3)
Quark coalescence model
does well explain the meson
and hadron v2 behavior
v2(ｂ) > v2(ｍ) @ high pt
D. Molnar, S.A. Voloshin,
nucl-th/0302014
How about heavier particle ?
(deuteron v2)
m2 distribution(1.0<pt(GeV/c)<2.0)
Fit:Gauss+exp
d+d-bar candidate
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PHENIX PRELIMINARY
Minimum bias
sNN = 200 GeV
m|2|<1.5σ(p)
Background
under exponential
mass2 [(GeV/c2)2]
v2 of d+d-bar is estimated by
subtracting backgrounds.
corr
dN
d

cand
dN
d

bg
dN
d
Clear mass dependence at low pt ;
deuteron v2 is smaller than proton v2
p-n coalescence model
Deuteron production ->final state
coalescence of p(p-bar) and n(n-bar).
 d 3N p 
d 3Nd

Ed
 B2  E p
3
3

dpd
dp p 

2
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- p,n coalescence prediction
v2
v2d(pt) = 2v2p(pt/2)
Minimum bias
sNN = 200 GeV
d-bar/d ratio vs. pt at Au+Au collision at
sqrt(SNN)=200GeV (quark matter 2002
Anuj K. Purwar and Rickard du Rietz)
pt[GeV/c]
hadron or quark flow ?
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Deuteron : coalescence of proton and neutron.
But if it’s scaled with quark numbers ・・・
hadron mass dependence seems to
be remaining even after nquark
scaling.
It might suggest that there are two
different flows (quark flow and
hadron flow) before and after
phase-transition or chemical freezeout.
Minimum bias
sNN = 200 GeV
Upgrade for identified particle v2 at higher pT page13
Integration
for run4 Au+Au
PMT
Volume
Aerogel
(11x22x11 cm^3)
PMT
80 box
Aerogel together with TOF can extend
the PID capability up to 10 GeV/c !.

electron v2
Why electron v2 ?
From Run1 result
g conversion
0  gee
h  gee, 30
w  ee, 0ee
  ee, hee
(PHENIX: PRL 88(2002)192303)
Clear excess above 1 GeV/c with
respect to photon conversion and
light hadron decay.
r  ee
h’  gee
c
The subtracted electron single
spectra is consistent with charm
decay (binary scaled).
“The high pt electron v2 can carry
information about the anisotropy
of the parent charmed mesons. “
inclusive electron / hadronic cocktail
b
direct g
(J. Alam et al. PRC 63(2001)021901)
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page15
Electron measurement at PHENIX
Electrons are identified as
Cherenkov right in RICH
Most hadrons do
not emit Cerenkov
light
mirror
Cerenkov
photons from e+
or e- are
detected by array
of PMTs
ＲＩＣＨ
- pt 0.2~4.9 GeV/c
• Number of hit PMT
• Ring shape
PMT array
PMT array
• E,p matching
Central Magnet
Electrons emit
Cerenkov
photons
in RICH.
page16
dn/d distribution
dn/d
v2e is corrected by
subtracting miss ID of electrons
e+(e-)
candidate
dN corr dN cand dN missID


d
d
d
-/2
cand --- dn/dphi of candidate
(detected RICH)
e+(e-)
miss ID --- dn/dphi of miss ID
e+(e-)
dn/d of after
Miss ID e+(e-)
/2
(dn/d)/N0
1.5
1.0
subtract Miss ID
e+(e-)
0.5
-/2
pt
/2
1.0
2.0
3.0
4.0
Pt dependence of v2(e)
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v2
electron v2 (“inclusive”)
(M.B)
Dalitz decays
Di-electron decays
Photon conversions
Kaon decays
Thermal dileptons
charm decay
beauty decay
Minimum bias
sNN = 200 GeV
pt[GeV/c]
Comparison with v2 of hadrons
v2
page18
<<Low pt (pt<1.0GeV/c)>>
v2 pion & v2 proton :
nucl-ex/0305013 (PHENIX)
v2(e) is larger than v2(pion)& v2 (proton)
v2
(proton)
v2 (pion)
v2(e)
-> dominant pi0 decay
- small decay angle
- decay from higher pt
<<High pt (pt>2.0GeV/c)>>
v2(e) seems to be smaller than v2 (pion)
(M.B)
particular interest because of the
contributions from heavy-quark
higher statistics needed.
x30 statistics expected in run4.
pt[GeV/c] (c/b) decays !(but the data
include another sources now)
What is needed to estimate
charmed electron v2 ?
e
p
c
dN
dN
dN


d
d
d
v2 ( c ) 
page19
v2( e )  rv2( p )
1 r
–Charm yield relative to inclusive electron yield at
sNN = 200 GeV (r= Np/Ne)
–v2(p) – flow of electrons originating photonic source
–Study v2 D->eX (due to large Q value)
Summary
• Elliptic flow (v2) of identified hadrons (/K/p/d/e) has been measured at
PHENIX.
+ hadron v2
– clear mass dependence observed at low pt region.
– consistent with hydrodynamical model (pT < 2.0 GeV/c). /K/p
– deviate hydro. and saturation (pT > 2.0 GeV/c). /K/p
– consistent with quark coalescence model (more or less).
– hadron mass dependence seem to be remaining after nquark scaling.
+ electron v2
- v2(e) is larger than v2 (pion) & v2 (proton) at low pt.
- v2(e) seems to be smaller than v2 (pion) at high pt. (indication)
+ higher pT data (high statistics) will be available in the next Run.
– detailed identifed hadron v2 study at intermediate to high pT region.
– high statistics v2(e) to determine charmed electron v2.
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