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High- p T Direct Photon Azimuthal Correlation Measurements

High- p T Direct Photon Azimuthal Correlation Measurements. Ahmed M. Hamed Texas A&M University University of Mississippi. XXIV QUARK MATTER DARMSTADT 2014. Contents Motivation Theoretical Predictions STAR Techniques Results ( √ s NN = 200 GeV ) Summary and Outlook.

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High- p T Direct Photon Azimuthal Correlation Measurements

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  1. High-pTDirect Photon Azimuthal Correlation Measurements AhmedM. Hamed Texas A&M University University of Mississippi XXIV QUARK MATTERDARMSTADT 2014

  2. Contents • Motivation • Theoretical Predictions • STAR Techniques • Results (√sNN = 200 GeV) • Summary and Outlook Ahmed M. Hamed May 2014

  3. Motivation: Parton Energy Loss in QGP • Energy loss: partoninitial energy, path length, color factor, quark flavor • EM interacting particles “high-pTphotons”: uniform hard scattering vertex in the QCD medium • 2-particles correlations (Df): • FF of the recoiling parton • from direct gand p0: • Parton initial energy “Compton-Scattering” • Different path length “on average” • Different q/g compositions • Observable: IAA = DAA/DNN • Reaction plane (Df): • Azimuthal anisotropy of p0and g • path length dependence of DE • Observable: v2 (pT) = < cos(2(fpT- yRP)) > Ahmed M. Hamed May 2014

  4. Theoretical Predictions Private Com. Renk, PRC 74 (2006) 034906 • Promptly produced EM-interacting particles of high-pTare expected to have no preferred direction w.r.t to the reaction plane, i.e. v2 = 0. ET(g) > 15 GeV ET(trig) > 8GeV • The medium effect is reflected in the FF of the recoiling partons at low zT: Large pT trigger (g / p0)OR Low pT associated (flow) • v2 (g) < 0 : jet-medium photons “Fries et al., PRL 90, 132301 (2003)” • v2(g) = 0 : direct photons “Compton Scattering” • v2(g) > 0 : frag. photons “Zakharov, JETP Lett. 80, 1 (2004)” Ahmed M. Hamed May 2014

  5. STAR Techniques (high-pTdirect g) • EM neutral cluster identifications (clustering algo., isolation cut) • EM transverse shower profile + Zgg: • EM neutral energy = p0 +other sources of EM neutral energy + g-rich sample • BEMC: | h | < 1.0, Df = 2p • TPC: | h | < 1.0, Df = 2p • FTPC: 2.5 < | h | < 4.0, Df = 2p • p0 purity, BG assumption justifications Ahmed M. Hamed May 2014

  6. Previous Results STAR, PRC 82, 034909 (2010) Au+Au @ 200 GeV (0-10%) 8 < ET(trg) < 16 GeV • v2(g) is finite. Event-plane reconstruction biases (non-flow) and/or Frag. photons contributions? • More forward detectors: 2.5 < | h | < 4.0 • Similar levels and patterns of IAA for p0 and • direct g. IAA shows no strong dependence on Ei • need to probe low zT Ahmed M. Hamed May 2014

  7. Integrated and Projected Luminosity in STAR • Current reconstructed data is sufficient • To probe the low zTregion and, • To measure the v2 using the STAR forward detector. Ahmed M. Hamed May 2014

  8. Particle Correlations -- IAA Private Com. ZT > 0.25 ET(trig) > 8GeV STAR Preliminary Au+Au @ 200 GeV (0-10%) Renk, PRC 74 (2006) 034906 ET(g) > 15 GeV • Both IAA of direct photons and p0 are flat within current uncertainties in the measured kinematics range Ahmed M. Hamed May 2014

  9. Reaction-plane Correlations: v2 • BEMC: | h | < 1.0, TPC: | h | < 1.0 • BEMC: | h | < 1.0, FTPC: 2.5 < | h | < 4.0 Au+Au @ 200 GeV Au+Au @ 200 GeV • v2of direct photon is consistent with zero within the current systematic errors • Remaining bias in reaction-plane determination is small when using forward detector • Fragmentation photons have negligible effect on overall v2 of direct photons • v2 < 0 : jet-medium photons • v2 = 0 : direct photons • v2 > 0 : frag. photons • v2of p0using the FTPC is apparently due • to the path length dependence of energy loss. Ahmed M. Hamed May 2014

  10. Summary and Outlook • STAR high-pT direct photon azimuthal and neutral pions, correlated with charged hadrons, measurements show: • The recoil parton from direct photons and p0observed to have constant softening in the QCD medium within the measured kinematic range (ET(trig) =12 - 24 GeV/c and pT(assoc) = 3 - 24 GeV/c)-- IAA is flat • The high-pT direct photons (8-20 GeV) is azimuthally uniform distributed w.r.t reaction plane -- v2 = 0 • More data to improve stat. and sys. errors, and explore further the low zT region. Stay tuned! Ahmed M. Hamed May 2014

  11. Thank you

  12. Backup Slides Ahmed M. Hamed May 2014

  13. D (zT) from different data sets I STAR Preliminary STAR Preliminary • The NS and AS conditional yields per • p0 from different data sets (pp2006, • dAu2008, and pp2009) agree over the • entire explored zT-range (0 - 2.0) . • The AS conditional yields per direct • photon from different data sets • (pp2006, dAu2008, and pp2009) agree • over many orders of mag. STAR Preliminary Ahmed M. Hamed May 2014

  14. D (zT) from different data sets III STAR Preliminary STAR Preliminary • The conditional yields per • p0 and direct g from different data sets • (AuAu 2007 and AuAu 2011) agree over the • entire explored zT-range STAR Preliminary Ahmed M. Hamed May 2014

  15. D (zT) from different data sets II • The conditional yields per • p0 and direct g from (AuAu 2011 and pp 2009) data shows expected trends. Ahmed M. Hamed May 2014

  16. EM Transverse Shower Profile Ahmed M. Hamed May 2014

  17. Previous Results-STAR vs. PHENIX • STAR and PHENIX have similar results using different techniques STAR Preliminary STAR Preliminary Ahmed M. Hamed May 2014

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