Azimuthal anisotropy of electrons in Au+Au collisions at √SNN=200GeV/c

measured with PHENIX at RHIC

Shingo Sakai

for PHENIX collaboration

Univ. of Tsukuba

Abstract

conversion0 ee

ee, 30

ee, 0ee ee, ee

ee

’ ee

The measurement of electrons and positrons at transverse momenta above 1.0 GeV/c allows to study the production of heavy flavor quark-anti quark pairs via the semileptonic decays of charmed particles [1]. The azimuthal anisotropy of high pt electrons can carry information about the anisotropy of the parent charmed mesons. The observation of charm flow would indicate that collective motion develops already in the partonic phase of the collision.

[1] (PHENIX: PRL 88(2002)192303)*Detail of single electron studies and new results in 200 GeV Au+Au Takashi Hachiya’s Poster

page1

The PHENIX experiment has the unique capability to measure electrons and positrons at RHIC. In this analysis we study the elliptic flow pattern of inclusive electrons from Au+Au collisions at √SNN= 200 GeV as function of transverse momentum and estimate “non-photonic” - charm & beauty - electron v2 subtracted all other electron sources, such as Dalitz decays and photon conversions.

direct (J. Alam et al. PRC 63(2001)021901)

b

c

PYTHIA

Overview of PHENIX

•Reaction plane is determined by BBC

•The tracking is done with DC+PC

•In the PHENIX experiment electrons are identified as Cherenkov light by RICH.

RICH -　 CO2

-　 0.2 <pt <5.0 　　　 (this analysis 0.4<pt<4.0) - 　 |y| 0.35

page2

dn/d of e distribution

Miss ID e+(e-) e+(e-)

candidate

In this analysis electron v2 is

estimated by using reaction plane

method. (measure azimuthal angle

of each electrons with respect to

the reaction plane )

Fig. shows the azimuthal distribution

of electrons which is measured with

respect to the reaction plane (upper

red). The blue histogram is miss ID electron. The bottom distribution is result which is subtracted miss ID electron and fitted by

dn/d = N(1+2v2cos(2* ))

page3

Pt dependence of e v2

Fig. shows pt dependence electron v2. The error bars reflect statistical errors only. The data points are plotted at the center of gravity of the bins as determined from the pt distribution and the horizontal error bar is RMS. The yellow line is systematic error. The electrons v2 are including “photonic” & “non-photonic” electrons v2.

Dalitz decaysDi-electron decays Photon conversionsKaon decaysThermal dileptons

charm decay beauty decay

“photonic”

“non-photonic”

page4

Comparison with v2 of hadrons

v2Fig. shows the comparison electron v2 and hadron v2 (pion,proton).

@Low pt (pt<1.0GeV/c)

v2(e) is larger than v2(pion)& v2

(proton)

@high pt region

This region particular interest because of the contributions from heavy-quark (c/b) decays is large.!

page5

Non-photonic electron v2

In this analysis we compare with electron v2 with simple model which is assuming charmed electron v2 is zero. And we also estimate non-photonic electron v2.

The azimuthal distribution of electron gives as;

dne/d = dnpho./d+ dnnon-pho./d

From the Eq. electron v2 is given as;

v2(e) = rv2(pho.)+(1-r)v2(non-pho.).

Here r is ratio of Ne/Npho.(shown right plot) and v2(pho.) is photonic e v2. The value is estimated by simulation (next page ).

ratio of Ne/Npho

@√sNN=200GeV (T.Hachiya)

page6

(1) photonic e v2 --- electron v2 from π0 and K

electron v2 (simulation)from K ( nucl-ex/0305013)

The dominant sources at low pt are photon conversions and Dalitz

decays of pi0 [1]. Electrons from Kaon decays contribute a few % at

Low pt. These electrons are also taken into consideration. Electron v2

from pi0 and K is estimated by simulation.

electron v2 (simulation)from pi0 (PHENIX preliminary )

page7

(2) e v2 compare with simple model

Fig. shows the comparison electron v2 and model v2

(electron v2 assuming non-photonic e v2=0). From the previous Eq. the v2 is estimated as;

v2= rv2(pho.)

The dashed line means systematic error of the model.

page8

(3) non-photonic e v2

Fig. shows non-photonic electron

v2 which is obtained by subtracting photonic v2 (pi0 & K decay electron) from electron v2.

v2(non-pho.) = {v2(e)-rv2(pho.)}/(1-r)

The result is compared with two

prediction of charmed electron &

D meson v2 which is based quark coalescence model .

v2(D) ≈ v2(light) + v2 （ charm ）

page9

charm quark

light quark

(4) non-photonic e v2 compare with model(1)

Charmed e v2 has been

predicted (nucl-th0312100)

with two scenario for charm quark distribution

(1)thermalization with transverse flow

(2) No reinteraction (PYTHIA spectra)

Here non-photonic e v2 is

compared with the scenario.

page10

(5) non-photonic e v2 compare with model(2)page11

D meson v2 has been

predicted (nucl-th0304045)

(1) D v2 (charm v2>0)

(2) D v2 (charm v2=0)

From the result we estimated

charmed electron v2 (triangles) .

Here non-photonic e v2 is

compared with D v2 & charm e v2

Summary

In this analysis we have measured the electron v2 by using the reaction plane method. With increasing pt the contribution from charm decays to the inclusive electron sample grows. We have compared the inclusive electron v2 with a simple model assuming that the charm v2 is zero. The model is consistent with the data within error bars.

We have also determined the "charmed electron" v2 by subtracting the "photonic electron" v2 from the inclusive data. The observed v2 of electrons from charm decays is consistent within errors with various model calculations which assume extremely different scenarios, no reinteraction of the initially produced charm quarks or complete thermalization with the bulk matter.

page12