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Ahmed M. Hamed Table of Contents: Elliptic Flow Measurements Introduction of Inclusive Photons Heavy-ion physics and STAR Detector Neutral Pions Reconstruction Physics at RHIC Physics with STAR BEMC oElliptic flow of inclusive photons. oNeutral pions reconstruction. Summary 1 Introduction: Levels of structure Atom is almost empty, Nucleus is crowdy ! eV 3.0 0 MeV Na Atom 3.0 0 GeV 208Pb Nucleus 0.3 0 Proton Nuclear density 0 ~ 0.15nucleons/fm3 Specific volume ~ 6fm3 Typical hadronic volume ~ 1-3 fm3 The average inter-nucleon distance in the nucleus ~ 1.8fm 2 Introduction: Forces -(r/a) hc e F~ 2 r Electromagnetic Force Strong Force =e/4hc 2 =g/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. 3 Introduction: Quantum Field Theories Quantum Chromodynamics Quantum Electrodynamics (Q2)= (Q02) s(Q2)= 1 (Q2) 0 ln(Q2/Q2) 10 2 1 2 = 3 1 1 >0 1 <0 QED QED lim (Q2)= Q2 QCD = s(Q02) 1 s(Q2) 0 ln(Q2/Q2) 10 2 2Nf - 11Nc 6 QCD lim s(Q2)=0 Q2 QCD exhibits confinement and asymptotic freedom. 4 Heavy-ion physics: Phases and D.o.F. The exact order of phase transition is not known. Smooth nature of the transition increases the experimental challenges. QGP near Tc should not be regarded as an ideal gas of quarks and gluons. 5 Heavy-ion physics Relativistic Heavy-Ion Collider Design Parameters: 6 Heavy-ion physics Space-time evolution QGP characteristics: Small size “ a few fermi in diameter” Very short life time 5-10x10-23 s. Scenarios of fireball formation: Landau Model: Full Stopping. Bjorken Model: Transparency. 7 Heavy-ion physics Signatures of QGP Small size and short-lived system. Kinematical and hydrodynamical Probes. Temperature, entropy, energy density, PT, dN/dy, dET/dy Electromagnetic Probes Dilepton productions. Direct Photons. Signatures from Deconfined phase. Strangeness enhancement. J/ Suppression. Indication of Chiral Symmetry Restoration. Hard QCD Probes. Jet quenching. Event-by-Event fluctuation. Hadronic Probes: +Large production rates - Final State Interactions. Electromagnetic Probes: +Large mean-free path compared to the size of the fireball system. -Huge hadronic background. 8 STAR Detector STAR Detector Tracker detectors(slow), Trigger detectors(fast), and Calorimeters(fast). 9 STAR Detector Barrel Electromagnetic Calorimeter =-ln tan(/2) Cross-section in Cross-section in 10 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. 11 Physics at RHIC: High Pt suppression The invariant cross section for 0production in pp collisions at s=200GeV agrees with NLO PQCD predictions over the range 2.0Pt15GeV/C. 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. 12 Physics with STAR BEMC Elliptic flow of inclusive photons Elliptic Flow of Inclusive Photons 13 Physics with STAR BEMC: Collective flow Longitudinal expansion Collective flow Radial transverse flow Directed flow Anisotropic transverse flow Elliptic flow Anisotropic flow correlations with respect to the reaction plane Higher harmonics flow = = dN const. d y V1=0 V1<0 V1>0 x V2< 0 y V2 > 0 V2 = 0 No symmetry in the configuration space anisotropy in the momentum space 2 is a measure of interactions in the system 14 x Physics with STAR BEMC: Direct real photons Non-Thermal photons: Thermal photons: 1. Prompt photons. 1. QGP photons. 2. Pre-equilibrium photons. 2. Hadron gas photons. Background Photons:Decayed photons. Schematic Photon Spectrum Bremsstrahlung n Low Pt: A+A collisions: Hard: 1/PT Thermal: e-E /T Photons don’t strongly interact with fireball. High pT Allow test of binary scaling for hard processes. Important for interpretation of high-pT hadron suppression at RHIC. 15 Physics with STAR BEMC: 2 of inclusive What is the origin of the binary scaling of direct photon? * “Jet quenching” photons. Bremsstrahlung Enhancement R.J.Fries, B. Muller and D.K.Srivastava, Phys.Rev. Lett. 90,132301 (2003) 2 of Direct photons: Scattering Suppression * Thermal Photons. Enhancement B.G. Zakharov, JETP Lett. 80, 1 (2004) -Help to disentangle the different production mechanism 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. STAR BEMC can probe for further higher transverse energy. 2 of inclusive photon is the first step toward 2 of direct photon. 16 Physics with STAR BEMC: Analysis details and technique Standard Method: |z|<=25 cm, Number of fit points>15, 0<pt<2GeV/C , Event plane reconstruction -1<<0 TPC, 2.6<<4.0 FTPC ,Number of tracks>10 TPC: 2 EP = atan2(i sin21 i+ i sin22 i , i cos21 i+ i cos22 i) FTPC: 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) ’s are the azimuthal angle of the tracks in the sub-events. W and E stand for the West and East sides of FTPC. Remove the acceptance bias: Event plane recentering: sin2 sin2 - M sin2 / M cos2 cos2 - M cos2 / M M: number of tracks in each sub-event Photons from BEMC: 2400 Towers 0.050.05 0<<1, 0<<2, E=0.16E Each track is extrapolated to the BEMC face and the charged particles veto cut for the target tower is used. Energy Threshold: Minimum Bias: ET>0.1GeV High Tower: ET>3GeV QA of BEMC: Check the uniformity of BEMC. Correlating inclusive photon with event plane: 2 Observed = cos(2tower- 2 EP) Finite multiplicity: Correction for event plane resolution: 2 Real= 2 Observed / R 17 Physics with STAR BEMC: 2 of inclusive result 2(Et) of inclusive photons integrated over unit pseudorapidity Au+Au MinBias o Au+Au High Tower Au+Au MinBias Au+Au High Tower Reaction plane from TPC 0<<1 Reaction plane from FTPC At low and intermediate ET,the 2(ET) behavior of inclusive is consistent with that of other mesons which indicate the dominance of 0 in that range. At high ET, although the statistical errors are large, it is clear that 2 decreases with Et but it is still finite. 18 Physics with STAR BEMC: Non-flow effect Scalar product method: The scalar product is the same for all collision systems in the case of only “nonflow”. The difference results from the collective motion and/or effects of medium modification. Au+Au MinBias 50%-80% o Au+Au High Tower 50%-80% p+p MinBias p+p High Tower 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 There is a clear contribution from the so called “non-flow” in TPC. The azimuthal correlations is dominated by nonflow effects at high Et. 19 Physics with STAR BEMC: Au+Au MinBias 50%-80% o Au+Au High Tower 50%-80% p+p MinBias p+p High Tower reducing non-flow effect 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 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(Et) of inclusive photons with that of hadrons is a promising sign for negligible amount of 2(Et) of direct photons. 20 Physics with STAR BEMC: Neutral pions reconstruction Neutral Pions Reconstruction 21 Physics with STAR BEMC: Reasons for new cluster finder dAu@200GeV Minbias dAu@200GeV High tower1 simulation [email protected] 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. 22 Physics with STAR BEMC: Cluster splitting New Cluster Finder: Energy seedTower&&SMDs>= 0.25GeV && >=0.2GeV Are the dots outside the band 0s ? Certainly they aren’t 0s with pt between 5 and 6GeV/c but they are 0 candidates for other pt bins. Is the asymmetry cut efficient here? It is obvious NO. 23 Physics with STAR BEMC: Cluster splitting removal 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 Pt Use the 0 decay kinematics to remove the cluster splitting. Cluster Splitting Removal 24 Physics with STAR BEMC: Cluster splitting removal check Accepted pairs Rejected pairs All Paris All Paris Rejected pairs Rejected pairs Accepted pairs Accepted pairs All pairs+ 0.3 All pairs+ 0.3 25 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. pp@200GeV pp@200GeV Simulation All Paris Rejected pairs Accepted pairs All pairs+ 0.3 dAu@200GeV MinBias dAu@200GeV High Tower 1 High tower1 dAu@200GeV High tower2 MinBias 26 Physics with STAR BEMC: New cluster finder results jkjh cucu@ 200GeV MinBias AuAu@200GeV AuAu@62GeV AuAu@200GeV AuAu@62GeV AuAu@200GeV 27 Summary oFirst measurements of the inclusive photon elliptic flow up to ET 15GeV have been done at RHIC energy with STAR BEMC. The elliptic flow of inclusive photons decreases with transverse momentum at high Pt but it is still finite up to Pt 15GeV. The finite value of inclusive photons elliptic flow at high Pt is mainly due to the nonflow effect. oA new cluster algorithm for STAR BEMC has been developed. The cluster splitting is highly suppressed in the new cluster finder. The neutral pion invariant mass peak is clearly seen in all different collsion systems at RHIC energy. oTwo important steps toward the final results of direct photons elliptic flow are made. 28 Thanks Many thanks to: Rene Bellwied Thomas Cormier Claude Pruneau Sergei Voloshin All STAR Collaborators And special thanks to all of you 29