09/15/10Waye State University1 Elliptic Flow of Inclusive Photon Ahmed M. Hamed Midwest Critical...

09/15/10 Waye State University 1

Elliptic Flow of Inclusive Photon

Ahmed M. Hamed

Midwest Critical MassUniversity of Toledo, Ohio

21-22 October, 2005

Wayne State University


Outline:

Outline

. Motivation

. Analysis details and technique

. Data and results

. Discussion

. Conclusion


Elliptic flow can provide early time information on the collectivity of particles from Heavy-ion collisions:

*Non-Central AA collisions result in an azimuthally anisotropic distribution of particles in coordinate-space.

*Density gradients and interactions between the particles lead to an Asymmetry in momentum-space.

*Signal is self-quenching with time-EARLY TIME OBSERVABLE!

Motivation: v2 Why?Rea

ctio

n pl

ane

Ou

t-of-

pla

ne

In-p

lane

=<y2 -x2 /y

2 +x2 >

V2=<P2x-P2

y/P2x+P2

y>


Higher harmonics flow

Partonic colle

ctivity

or Hadronic

collectiv

ity!

V1<0V2<0

Anisotropic flow

Directed flow

Elliptic flowCorrelations w.r.t the reaction plane

Overall shift in the transverse plane

V1>0 V2>0

v2 is a measure of interactions in the system

v2=<cos(2)>v2=<cos(2)>

* Expanding in Fourier series:

E(d3N/d3P)=1/ (d2N/d2pTdy)[1+2v1cos()+2 v2 cos(2)+…]

FlowRadial/Isotropic flow

V1=0

x

y

V2=0

x

y

Azimuthal Distribution

vn=<cos(n(-r))>

Motivation: v2 How?


solid: STARopen: PHENIX PRL91(03)

Partonic collectivity is an expected attribute of a QGPPartonic collectivity is an expected attribute of a QGP

Motivation: v2

Result


Direct Real Photons:

Non-Thermal photons:

1. Prompt photons.

2. Pre-equilibrium photons.

Thermal photons:

1. QGP photons.

2. Hadron gas photons.

Background Photons:Compton-like

Annihilation

Bremsstrahlung

Hadron decay

, etc.

Tu

rbid

e, R

app

, Gal

e, P

hys

.

Rev

. C 6

9 (0

1490

3), 2

004Realistic Calculation

Motivation: which Photons?

nT

1

phard:

/ E TeThermal

Schematic Photon Spectrum

Decay photons


Motivation: Why Photons?

p+p collisions:* Test of QCD.* Constraining gluon distribution functions.* In polarized p+p also gluon spin structure function.

A+A collisions:# Photons don’t strongly interact with fireball.

* Carry information about early stage of collision.

# Direct Photons at high pT

* Allow test of binary scaling for hard processes.

* Important for interpretation of high-pT hadron suppression at RHIC.

* QGP potentially detectable via thermal photon radiation:Thermal photons dominantly from early, hot QGP phase

initial temperature.


Motivation: Photons result

* 0’s suppressed going to central collisions.

* Direct photons consistent with NLO pQCD “binary scaling”.

* 0 suppression caused by medium created in A+A collisions.

PHENIX preliminary* The pT and centrality dependences of 0 and inclusive v2 is consistent

with that of other mesons.

* The measured v2 of inclusive is

consistent with the v2 of from hadronic decays.* v2=0 for direct photons.


Motivation: v2 of inclusive photons Why? * “Jet quenching” photons.

EnhancementR.J.Fries, B. Muller and

D.K.Srivastava, Phys.Rev. Lett. 90,132301

(2003)

SuppressionB.G. Zakharov, JETP

Lett. 80, 1(2004)

Bremsstrahlung Scattering

What is the origin of the binary scaling of direct photon?

* Thermal Photons.Enhancement

Summary:

* Measuring v2 of Direct photons:-Help to disentangle the different production mechanism of direct photon.

* STAR can probe for further higher transverse energy.* v2 of inclusive photon is the first step toward v2 of direct photon.

Coulomb and Annihilation: v2=0Coulomb and Annihilation: v2=0 Scattering: v2>0Scattering: v2>0 Similar to hadrons

Bremsstrahlung: v2<0

-Thermal photons reflect the dynamical evolution of the formed matter.

* At very high PT v2 will be dominated by direct photon due to the large suppression of 0.


STAR TPC and FTPC to reconstruct the event plane

0<pt<2GeV/C ,

|z|<=25 cm, Number of fit points>15

-1<<0 TPC

2.6<<4.0 FTPC , Number of tracks>10

2400 Towers 0.050.050<<1, 0<<2,E=0.16E

STAR BEMC

Analysis details and technique

Energy Threshold:Minimum Bias: >0.1GeVHigh Tower: >3GeV


Analysis details and technique* Event plane reconstruction:

2 EP = atan2(i sin21 i+ i sin22 i , i cos21 i+ i cos22 i)

2EP = atan2(i sin2w1 i+ i sin2w2 i + i sin2E1 i+ i sin2E2 i , i

cos2w1 i+ i cos2w2 I + i cos2E1 i+ i cos2E2 i)

TPC:

FTPC:

* Event plane recentering:sin2 cos2

sin2 - M sin2 / M cos2 - M cos2 / M M: number of tracks in each sub-event

* Check the uniformity of BEMC.

* Correlating inclusive photon with event plane:v2 = cos(2- 2 EP)

* Correction for event plane resolution:

v2 Real= v2 Observed /


Data and results : AuAu @ s=200 GeV. Run IV. 10.2M events. Event plane


Data and results: BEMC Uniformity-Minimum Bias.


Data and results: BEMC Uniformity-High Tower.


Data and results: v2


Discussion

- The ET dependences of inclusive v2 is consistent with that of other mesons which indicate the dominance of 0 in that range.

- The v2 reaches its maximum at ~ 3GeV which is consistent with that of other hadrons.

* At low ET(ET<2GeV):

* At intermediate ET:

- Nice matching between the minimum bias and high towers data.

* At High ET:

- The present produced statistics is small, however the measurements indicate that the v2 has non-zero value.


Conclusion* The azimuthal anisotropy is a powerful tool to study the early

stage of ultra-relativistic nuclear collision.

* Direct photon is one of the most promising signature of QGP.

* No Direct photon signal is observed yet in the available pT range.

* At very high PT , v2 will be dominated by direct photon due to the large suppression of 0.

* The v2 measurement of direct photons would help to disentangle the various scenarios of direct photon production.

* The v2 measurement of direct photons would provide more information on the dynamic and properties of the produced hot and

dense matter.

* Measurement of 0 can reach very high pT and thus should permit study of the effect of hard processes, e.g. jet quenching, on v2.


The End, Thank You

09/15/10Waye State University1 Elliptic Flow of Inclusive Photon Ahmed M. Hamed Midwest Critical...

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