1. 1 Ph.D. Defense Public Presentation Ahmed M. Hamed Elliptic Flow Measurements of Inclusive Photons and Neutral Pions Reconstruction Ahmed Hamed WSU 07-05-06 Table of Contents:  Introduction  Physics at RHIC  Physics with STAR BEMC  Heavy-ion physics  Summary oElliptic flow of inclusive photons. oNeutral pions reconstruction.  STAR Detector

2. 2 Introduction: Levels of structure Ahmed Hamed WSU 07-05-06 3.0 0 eV Na Atom 3.0 0 MeV 208 Pb Nucleus 0.3 0 GeV Proton  Nuclear density  0 ~ 0.15nucleons/fm 3  Specific volume ~ 6fm 3  Typical hadronic volume ~ 1-3 fm 3  The average inter-nucleon distance in the nucleus ~ 1.8fm Atom is almost empty, Nucleus is crowdy !

3. 3 Introduction: Forces Ahmed Hamed WSU 07-05-06 Electromagnetic Force Strong Force  =e/4  hc 2 a=  a=10 -13 cm  The force itself is carried by elementary particles, namely, by the continuous exchange of zero mass bosons between the two charges.  The macroscopic, classical force results from the average effect of the bosons exchange.  hc F ~ r 2 -(r/a) e  =g/4  hc 2

4. 4 Introduction: Quantum Field Theories Ahmed Hamed WSU 07-05-06 Quantum Electrodynamics Quantum Chromodynamics  QCD exhibits confinement and asymptotic freedom. 1-  (Q 2 )=  (Q 2 ) 0 11 0 22 ln(Q 2 /Q 2 ) 0 11 QED = 2 3  s (Q 2 )=  s (Q 2 ) 0 1- 11  s (Q 2 ) 0 22 ln(Q 2 /Q 2 ) 0 = 11 QCD 2N f - 11N c 6 lim  s (Q 2 )=0 Q2Q2  lim  (Q 2 )=  Q2Q2  11 QED >0 QCD 11 <0

5. 5 Heavy-ion physics: Phases and D.o.F. Ahmed Hamed WSU 07-05-06  Smooth nature of the transition increases the experimental challenges.  The exact order of phase transition is not known.  QGP near T c should not be regarded as an ideal gas of quarks and gluons.

6. 6 Heavy-ion physics Relativistic Heavy-Ion Collider Ahmed Hamed WSU 07-05-06 Design Parameters:

7. 7 Heavy-ion physics Space-time evolution Ahmed Hamed WSU 07-05-06 Scenarios of fireball formation: Landau Model: Full Stopping. Bjorken Model: Transparency. QGP characteristics: Small size “ a few fermi in diameter” Very short life time 5-10x10 -23 s.

8. 8 Heavy-ion physics Signatures of QGP Ahmed Hamed WSU 07-05-06  Kinematical and hydrodynamical Probes.  Electromagnetic Probes  Signatures from Deconfined phase.  Indication of Chiral Symmetry Restoration.  Hard QCD Probes. Jet quenching. Strangeness enhancement. J/  Suppression. Dilepton productions. Temperature, entropy, energy density, P T, dN/dy, dE T /dy Direct Photons.  Event-by-Event fluctuation. +Large production rates- Final State Interactions. -Huge hadronic background. +Large mean-free path compared to the size of the fireball system. Hadronic Probes: Electromagnetic Probes:  Small size and short-lived system.

9. 9 STAR Detector Ahmed Hamed WSU 07-05-06  Tracker detectors(slow), Trigger detectors(fast), and Calorimeters(fast).

10. 10 Ahmed Hamed WSU 07-05-06 STAR Detector Barrel Electromagnetic Calorimeter  =-ln tan(  /2) Cross-section in  Cross-section in 

11. 11 Physics at RHIC: Collectivity  Hydrodynamic calculations assume local thermal equilibrium in the early stage t  1 fm/c to reproduce the magnitude of the observed 2 at RHIC. Ahmed Hamed WSU 07-05-06

12. 12  The invariant cross section for  0 production in pp collisions at  s=200GeV agrees with NLO PQCD predictions over the range 2.0  P t  15GeV/C. Physics at RHIC: High P t suppression  The suppression of  0, s and , s is very similar which supports the conclusion that the suppression occurs at the parton level.  The binary scaling of direct photons is strong evidence that the suppression is not an initial state effect. Ahmed Hamed WSU 07-05-06

13. 13 Physics with STAR BEMC Elliptic flow of inclusive photons Elliptic Flow of Inclusive Photons Ahmed Hamed WSU 07-05-06

14. 14 Physics with STAR BEMC: Collective flow Collective flow Longitudinal expansion Radial transverse flow Anisotropic transverse flow Directed flow Elliptic flow V2<0V2<0 x y V2>0V2>0 V2=0V2=0 V 1 <0 x y V 1 >0 V 1 =0 Higher harmonics flow Anisotropic flow  correlations with respect to the reaction plane No symmetry in the configuration space anisotropy in the momentum space dN dd  const. = =  2 is a measure of interactions in the system Ahmed Hamed WSU 07-05-06

15. 15 Schematic Photon Spectrum Non-Thermal photons: 1. Prompt photons. 2. Pre-equilibrium photons. Thermal photons: 1. QGP photons. 2. Hadron gas photons. Background Photons:Decayed photons. A+A collisions:  Photons don’t strongly interact with fireball. High p T  Allow test of binary scaling for hard processes.  Important for interpretation of high-p T hadron suppression at RHIC. Low P t : Physics with STAR BEMC: Direct real photons Bremsstrahlung Hard: 1/P T n Thermal: e - E  /T Ahmed Hamed WSU 07-05-06

16. 16 * “Jet quenching” photons. Enhancement R.J.Fries, B. Muller and D.K.Srivastava, Phys.Rev. Lett. 90,132301 (2003) Suppression B.G. Zakharov, JETP Lett. 80, 1 (2004) Bremsstrahlung Scattering What is the origin of the binary scaling of direct photon? * Thermal Photons. Enhancement  2 of Direct photons: -Help to disentangle the different production mechanism of direct photon.  STAR BEMC can probe for further higher transverse energy.  2 of inclusive photon is the first step toward 2 of direct photon. Coulomb: 2 =0 Scattering: 2 >0 “tracks hadronic 2 ” Bremsstrahlung: 2 <0 -Thermal photons reflect the dynamical evolution of the formed matter. Physics with STAR BEMC: 2 of inclusive  Ahmed Hamed WSU 07-05-06

17. 17 0<pt<2GeV/C,|z| 15,  Event plane reconstruction -1<  <0 TPC,2.6<  <4.0 FTPC, Number of tracks>10 TPC: 2  EP = atan2(  i sin2  1 i +  i sin2  2 i,  i cos2  1 i +  i cos2  2 i ) FTPC: 2  EP = atan2(  i sin2  w1 i +  i sin2  w2 i +  i sin2  E1 i +  i sin2  E2 I,  i cos2  w1 i +  i cos2  w2 I +  i cos2  E1 i +  i cos2  E2 i )  Correlating inclusive photon with event plane: 2 Observed =  cos(2  tower - 2  EP )  Physics with STAR BEMC: Analysis details and technique  Photons from BEMC: Each track is extrapolated to the BEMC face and the charged particles veto cut for the target tower is used. Energy Threshold:Minimum Bias: E T >0.1GeV High Tower: E T >3GeV 2400 Towers 0.05  0.050<  <1,0<  <2 ,  E=0.16  E Standard Method:  Event plane recentering: M: number of tracks in each sub-event sin2  sin2  - M  sin2  / M  cos2  cos2  - M  cos2  / M   Remove the acceptance bias:  Check the uniformity of BEMC.  QA of BEMC:  Correction for event plane resolution: 2 Real = 2 Observed / R  Finite multiplicity: Ahmed Hamed WSU 07-05-06  ’s are the azimuthal angle of the tracks in the sub-events. W and E stand for the West and East sides of FTPC.

18. 18  Au+Au MinBias o Au+Au High Tower  Au+Au MinBias  Au+Au High Tower Reaction plane from TPC Reaction plane from FTPC 0<  <1 Physics with STAR BEMC: 2 of inclusive  result  At low and intermediate E T,the 2 (E T ) behavior of inclusive  is consistent with that of other mesons which indicate the dominance of  0 in that range.  At high E T, although the statistical errors are large, it is clear that 2 decreases with E t but it is still finite. 2 (E t ) of inclusive photons integrated over unit pseudorapidity Ahmed Hamed WSU 07-05-06

19. 19 Physics with STAR BEMC: Non-flow effect  The difference results from the collective motion and/or effects of medium modification.  There is a clear contribution from the so called “non-flow” in TPC.  Au+Au MinBias 10%-50% o Au+Au High Tower 10%-50%  p+p MinBias  p+p High Tower  Au+Au MinBias 0%-10% o Au+Au High Tower 0%-10%  p+p MinBias  p+p High Tower  Au+Au MinBias 50%-80% o Au+Au High Tower 50%-80%  p+p MinBias  p+p High Tower  The scalar product is the same for all collision systems in the case of only “nonflow”.  The azimuthal correlations is dominated by nonflow effects at high E t. Scalar product method: Ahmed Hamed WSU 07-05-06

20. 20  Au+Au MinBias 10%-50% o Au+Au High Tower 10%-50%  p+p MinBias  p+p High Tower  Au+Au MinBias 50%-80% o Au+Au High Tower 50%-80%  p+p MinBias  p+p High Tower  Au+Au MinBias 0%-10% o Au+Au High Tower 0%-10%  p+p MinBias  p+p High Tower Physics with STAR BEMC: reducing non-flow effect  The non-flow contribution in FTPC is very negligible.  The behavior of the azimuthal correlations with centrality shows strong evidence for elliptic flow at low and moderate Et.  The quantitative similarity between 2 (E t ) of inclusive photons with that of hadrons is a promising sign for negligible amount of 2 (E t ) of direct photons. Ahmed Hamed WSU 07-05-06

21. 21 Physics with STAR BEMC: Neutral pions reconstruction Neutral Pions Reconstruction Ahmed Hamed WSU 07-05-06

22. 22 dAu@200GeV High tower1 AuAu@62.4GeV simulation dAu@200GeV Minbias Physics with STAR BEMC: Reasons for new cluster finder  Strong peak at low invariant mass region.  No  0 invariant mass peak is seen in the high multiplicity system.  No low invariant mass peak in simulation. Ahmed Hamed WSU 07-05-06

23. 23 Physics with STAR BEMC: Cluster splitting  Are the dots outside the band  0 s ?  Is the asymmetry cut efficient here? It is obvious NO. Certainly they aren’t  0 s with p t between 5 and 6GeV/c but they are  0 candidates for other p t bins. New Cluster Finder: Energy seed Tower&&SMDs >= 0.25GeV && >=0.2GeV Ahmed Hamed WSU 07-05-06

24. 24  No successful study for the EM shower shape so far using STAR BEMC.  No cluster splitting effect for the large opening angle decayed photons.  The distribution is peaked heavily around the minimum opening angle.  The energy threshold is already greater than energy of one of the decayed photon in the asymmetric decay case for  0 with low P t  Use the  0 decay kinematics to remove the cluster splitting. Physics with STAR BEMC: Cluster splitting removal Ahmed Hamed WSU 07-05-06 Cluster Splitting Removal

25. 25 Accepted pairs Physics with STAR BEMC: Cluster splitting removal check Rejected pairs All Paris Rejected pairs Accepted pairs All pairs+   0.3 All Paris Rejected pairs Accepted pairs All pairs+   0.3 Ahmed Hamed WSU 07-05-06

26. 26 pp@200GeV All Paris Rejected pairs Accepted pairs All pairs+   0.3 Simulation High tower1 MinBias dAu@200GeV High tower2 High Tower 1 MinBias Physics with STAR BEMC: New cluster finder results Extrapolate the track to the BEMC face and set the energy of the target tower to zero. Ahmed Hamed WSU 07-05-06

27. 27 AuAu@62GeV AuAu@200GeV AuAu@62GeV jkjh cucu@ 200GeV MinBias Physics with STAR BEMC: New cluster finder results Ahmed Hamed WSU 07-05-06

28. 28 Summary  The elliptic flow of inclusive photons decreases with transverse momentum at high P t but it is still finite up to P t  15GeV.  The finite value of inclusive photons elliptic flow at high P t is mainly due to the nonflow effect.  The cluster splitting is highly suppressed in the new cluster finder. oTwo important steps toward the final results of direct photons elliptic flow are made.  The neutral pion invariant mass peak is clearly seen in all different collsion systems at RHIC energy. Ahmed Hamed WSU 07-05-06 oFirst measurements of the inclusive photon elliptic flow up to E T  15GeV have been done at RHIC energy with STAR BEMC. oA new cluster algorithm for STAR BEMC has been developed.

29. 29 Many thanks to: Rene Bellwied Claude PruneauThomas CormierSergei Voloshin All STAR Collaborators And special thanks to all of you Thanks Ahmed Hamed WSU 07-05-06