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Electron and identified hadron v2 to look for hadronic or partonic origi
n of elliptic flow
Shingo Sakai
for the PHENIX Collaboration
Univ. of Tsukuba
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
page1
Introduction
Why identified v2 ?
x
y
p
x
p y
Initial spatial anisotropy
Momentum space anisotropy
of particle emission
-> Low pt - pressure gradient of early stage of collision - hydrodynamical behavior -> High pt
- parton energy loss in hot & dense medium
The azimuthal anisotropy of particle
emission reflects
Measurement of identified particle v2 gives us much more information of the collision dynamics
page2
Measurement of v2
<<Reaction Plane Method>>
dN/d(-) = N (1 + 2v2obscos(2(-)))
: azimuthal angle of reaction plane : azimuthal angle of particle v2
obs: strength of azimuthal anisotropy
(fitting of dn/d(-) or v2=<cos2(-)>) v2 = v2
obs/ σ
σ=<cos(2(m-real))> = {<cos(2(A-B))>}1/2
Reaction
Plane
X
Y
wi*sin(2i) tan2 rp =
wi*cos(2i)
Measure azimuthal angle of each particle with respect to the reaction plane
r.p-
e
page3
Over view of PHENIX detectorCharged Particle Tracking:
Drift ChamberPad ChamberTime Expansion Chamber
Particle ID:Time of Flight Ring Imaging Cerenkov CounterTECMuon ID (PDT’s)
Calorimetry:Pb ScintillatorPb Glass
Event CharacterizationBeam-Beam CounterZero Degree Calorimeter
page4
hadron v2
Phenix (East-Arm)
Hadron measurement @ PHENIX
- 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
The PHENIX experiment has the high
timing resolution TOF counter.
page5
Particle ID
π
K
mass2 [(GeV/c2)2]
P
d
mass2 [(GeV/c2)2]
Momentum [GeV/c]
Clear signal peaks
PID : m2 = p2 {(TOF/L)2 -1}
page6
Reaction plane
r.p resolution<cos(2(A-real))> = {<cos(2(A-B))>}1/2
Correlation r.p BBC_north & r.p BBC_south
Centrality [%]
v2 =v2 obs / resolution
central peripheral
Determine r.p using BBC north and south
Page 7
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 hydrodyna
mical behavior is observed.– Saturation at intermediate pT.
page8
Quark coalescence model
/3)(p3v)(pv
/2)(p2v)(pv
Tq2,TB2,
Tq2,TM2,
Quark coalescence model
Quark coalescence model does well explain the meson and hadron v2 behavior
v2( b ) > v2( ) @ high p
t
D. Molnar, S.A. Voloshin, nucl-th/0302014
nucl-ex/0305013 (PHENIX)
page9
How about heavier particle ?(deuteron v2)
Clear mass dependence at low pt ;
deuteron v2 is smaller than proton v2
v2 of d+d-bar is estimated by subtracting backgrounds.
d
dN
d
dN
d
dN bgcandcorr
m2 distribution(1.0<pt(GeV/c)<2.0)
mass2 [(GeV/c2)2]
Backgroundunder exponential
d+d-bar candidate
m2|<1.5σ(p)
Fit:Gauss+exp
|
Minimum biassNN = 200 GeV
PHENIX PRELIMINARY
page10
p-n coalescence model
v2d(pt) = 2v2
p(pt/2)
Deuteron production ->final state coalescence of p(p-bar) and n(n-bar). - p,n coalescence prediction
2
3
3
23
3
p
pp
d
dd dp
NdEB
dp
NdE
d-bar/d ratio vs. pt at Au+Au collision at sqrt(SNN)=200GeV (quark matter 2002 Anuj K. Purwar and Rickard du Rietz)
Minimum biassNN = 200 GeV
v2
pt[GeV/c]
page11
hadron or quark flow ?
Minimum biassNN = 200 GeV
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 freeze-out.
page12
Upgrade for identified particle v2 at higher pT
Aerogel together with TOF can extend
the PID capability up to 10 GeV/c !.
Integration Volume
PMT
PMT
Aerogel(11x22x11 cm^3)
for run4 Au+Au
80 box
page13
electron v2
Why electron v2 ?
conversion0 ee
ee, 30
ee, 0ee ee, ee
ee
’ ee
inclusive electron / hadronic cocktail
Clear excess above 1 GeV/c with respect to photon conversion and light hadron decay.
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. “
direct (J. Alam et al. PRC 63(2001)021901)
b
c
(PHENIX: PRL 88(2002)192303)From Run1 result
page14
Electron measurement at PHENIX
Electrons are identified as
Cherenkov right in RICH
- pt 0.2~4.9 GeV/c
• Number of hit PMT
• Ring shape
• E,p matching
Cerenkov photons from e+ or e- are detected by array of PMTs
mirror
Most hadrons do not emit Cerenkov light
Electrons emit Cerenkov photonsin RICH.
Central Magnet
RICH
PMT arrayPMT array
page15
dn/d distribution
2.0 3.0 4.0pt
Miss ID e+(e-)
dn/d of after
subtract Miss ID
e+(e-)
v2e is corrected by
subtracting miss ID of electrons
d
dN
d
dN
d
dN missIDcandcorr
e+(e-)
candidate
cand --- dn/dphi of candidate (detected RICH) e+(e-)miss ID --- dn/dphi of miss ID e+(e-)
dn/d
(dn/d)/N0
-
-
1.0
1.5
0.5
1.0
page16
Pt dependence of v2(e)
(M.B)
pt[GeV/c]
v2
electron v2 (“inclusive”)
Dalitz decaysDi-electron decays Photon conversionsKaon decaysThermal dileptonscharm decay beauty decay
Minimum biassNN = 200 GeV
page17
Comparison with v2 of hadrons
v2 (proton)
v2 (pion)
v2(e)
v2 pion & v2 proton :
nucl-ex/0305013 (PHENIX)
pt[GeV/c]
v2
(M.B)
<<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
<<High pt (pt>2.0GeV/c)>>
v2(e) seems to be smaller than v2 (pion)
particular interest because of the
contributions from heavy-quark
(c/b) decays !(but the data include another sources now)
higher statistics needed.
x30 statistics expected in run4.
page18
What is needed to estimate charmed electron v2 ?
d
dN
d
dN
d
dN cpe
r
rvvv pe
c
1
)(2)(2)(2
–Charm yield relative to inclusive electron yield at s
NN = 200 GeV (r= Np/Ne)
–v2(p) – flow of electrons originating photonic source
–Study v2 D->eX (due to large Q value)
page19
Summary• Elliptic flow (v2) of identified hadrons (/K/p/d/e) has been measured at PHE
NIX.+ 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.
page20