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