Measurements of the anysotropic differential elliptic flow v

Measurements of the anysotropic (differential) elliptic flow v 2(pt) = <cos(2 f)>pt of photons based upon run 2 Au. Au data. Shin. Ichi Esumi Saskia Mioduszewski Edouard Kistenev Motivation; Selection of the data; Simulation and validity range; Preliminary data presentation; Summary

Probing collective dynamics in Au. Au interactions Reaction plane: Defined by the particles produced outside the central rapidity region (y>>1 to suppress the short range correlations in rapidity space) py px z y x initial spatial anisotropy isotropic anisotropy in momentum space directed elliptic S. Esumi

Indirect way to study hard processes (jets and direct photons); flow+jets flow only (wrong!) flow + flow&jets cross term V 2 jet=0 : reduce v 2 just as BG V 2 jet>0 : almost no change or increase in v 2 jets only track 1 - track 2 S. Esumi

Extracting v 2 particle i average direction i raw σrp = <cos(2( m- real))> = {<cos(2( A- B))>}1/2 raw

Why photons: -extend the pt range for identified particles: pt range covered by charged hadrons < 5 Ge. V/c compared to >10 Ge. V/c for photons; -near saturation in the v 2 values is observed above 2 Ge. V/c while Back of the envelope diffuse nuclei calculations predict rapid decrease of v 2 above pt>3 -4 Ge. V/c contrary to “claims” of saturation. Identified photons are the ideal tool to solve the puzzle.

Data selection TOF (within 2 s of gamma-flash) Shower shape (c 2<3); AB No charged track hit within e/m cluster isolation window

g’s vs p 0’s – daughters and mothers (simulation)

Statistics and validity range (simulation)

Systematics and validity range different methods for extracting v 2 different reaction planes methods different colors for the sys. errors.

PHENIX preliminary

Comparison to the flow probed with charged hadrons

Comparison to the flow probed with p 0’s

Summary -angular distribution of photons with respect to reaction plane is sensitive to the flow as seen in collisions of nucleus; -in the presently accessible range of the photon transverse momenta (<5 Ge. V/c) the centrality and pt dependence of the flow as probed by photons is consistent with that observed with charged hadrons; -our measurements indicate continuous decrease in the flow with transverse momenta. There can be a hint of a behavior difference between photons and p 0’s in PHENIX data. We very much hope to resolve this issue with more data to come.

The end