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-measurements

-measurements. Saskia Mioduszewski. Martin Codrington. Texas A&M Group Ahmed M. Hamed. BNL 10-17-07. -measurements. +nucleus e - +e + +nucleus. e+nucleus e - ++nucleus.

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-measurements

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  1. -measurements Saskia Mioduszewski Martin Codrington Texas A&M Group Ahmed M. Hamed BNL 10-17-07

  2. -measurements +nucleus e-+e++nucleus e+nucleus e-++nucleus Texas A&M Group Ahmed M. Hamed BNL 10-19-07 Table of Contents: • Motivation • Single particle spectra • Jet-like azimuthal correlations •  in Spin physics • -measurements • Experimental Challenges • Experimental Technique • Previous -jet measurements at STAR • Preliminary Results of -triggered 2007 Data • -trigger in Run 2007 • Status and first look • Shower Shape Analysis • Comparison of shower shape in MC and Real data • Effect of BSMD saturation on shower shape analysis • Summary

  3. Motivation Why -measurements? Single Particle Spectra-RAA? Texas A&M Group Ahmed M. Hamed BNL 10-19-07 p+p  jet+jet Au+Au ??? • QCD is written in terms of q&g degrees of freedom! • Study FF from ee+ collisions and PDF from pp collisions! • PDF in nuclear environment !FF in medium! • NLO pQCD agrees with RHIC measurements for high pt particles at mid-rapidity. • Nuclear modification factor: • How to compare AA to pp?

  4. Motivation Why -jet measurements? Single Particle Spectra-RAA Mid-rapidity Statistical Method Texas A&M Group Ahmed M. Hamed BNL 10-19-07 <E>  sCxqL “Static medium” • Heavy quarks suppress as much as light quarks in the medium. • No reduction is “as expected” observed in the baryon/meson ratio as in the gluon dominance picture. Forms of energy loss, s(T)? • RAA exhibits only very limited sensitivity to the properties of the medium. • More differential observable is needed.

  5. Motivation Why -jet measurements? Jet-like azimuthal correlations ? Texas A&M Group Ahmed M. Hamed BNL 10-19-07 • Near-side: p+p, d+Au, Au+Au is similar. • Back-to-back: Au+Au strongly suppressed relative to p+p and d+Au. Suppression of the back-to-back correlation in central Au+Au is a final-state effect • Surface bias for the trigger particle. • Trigger particle with no surface bias is required for better calibration of the away-side jet.

  6. Texas A&M Group Ahmed M. Hamed BNL 10-19-07 Motivation Why -jet measurements?Spin Physics • p+p gluon density • Direct photons have the gluon distribution information

  7. Motivation Why -jet measurements? Summary Texas A&M Group Ahmed M. Hamed BNL 10-19-07 Four multipurpose experiments (BRAHMS, PHENIX, PHOBOS, STAR) • Empirical lines of evidence: Energy density well beyond critical value. Large elliptic flow. Jet quenching. dAu control experiment. • Interpreted in terms of a strongly coupled QGP and a new QCD state (?) Color Glass Condensate Required: • Better understanding for the energy loss mechanism! • Direct Photons: Doesn’t couple to the medium. • QGP thermal photons. • Elliptic flow. • Test for binary scaling for hard process. -jet measurements • Gamma-charged hadrons correlation. • Challengeable measurements!

  8. schematic view thermal: Decay photons hard: Texas A&M Group Ahmed M. Hamed BNL 10-19-07 Motivation Why -jet measurements?LODirect photons direct component Bremsstrahlung fragmentation component • Gamma-charged hadrons correlation. • Calibrated probe of the QGP – at LO. • No Surface Bias • Hard process • Possible discriminator for quark/gluon jet at LO.

  9. Texas A&M Group Ahmed M. Hamed BNL 10-19-07 Motivation Why -jet measurements?Spin Physics -jet measurements on statistical basis Inclusive -jet correlation function 0-jet (h-jet) correlation function direct-jet = iclusive-jet-decay-jet “taking into account decay kinematics”.

  10. Experimental Challenges Is it possible to measure? Texas A&M Group Ahmed M. Hamed BNL 10-19-07 In medium: • 0–spectra are suppressed by a factor of ~5 relative to the scaled p+p collisions. • The away-side in di-jet production is more suppressed. Pythia v6.131 event generator pp-collisions at √s=200 GeV, |η|<1 (STAR acceptance) • Background sources of direct photons suppressed in medium.

  11. Experimental Challenges Is it possible to measure? Texas A&M Group Ahmed M. Hamed BNL 10-19-07 Inclusive g-jet in Au+Au at s=200GeV SIMULATION (pp) p0 simulation STAR Preliminary Thomas Dietel Quark Matter 2005 photon simulation • Simulation shows no associated particles in -charged correlation. • Away-side decreases with increasing centrality. • Decrease in near-side due to the increased fraction of prompt photons. • Need /0 discrimination.

  12. Experimental Challenges Is it possible to measure? Texas A&M Group Ahmed M. Hamed BNL 10-19-07 S. Chattopadhyay Quark Matter 2006 p0Bin • Reduction in near angle peak towards photon Bin. • Effect is more prominent for larger Ettrigger . Mixed g Bin More discrimination power is needed in the high multiplicity system

  13. Experimental Challenges Is it possible to measure? -plane -plane Texas A&M Group Ahmed M. Hamed BNL 10-19-07 0 DECAY KINEMATICS min= 2 Sin –1 (mInv /E),  ~10-17 s Towers (~0.05x~0.05), Strips (~0.007x~0.007), d ~2.2m at =0, l~2.93m. Opening angle(rad) • Electromagnetic transverse shower characteristics • High energy core. • Low energy halo. 0’s pT(GeV/c)

  14. L2 Gamma Trigger in Run 2007 Texas A&M Group Ahmed M. Hamed BNL 10-19-07 • Tower threshold ET=5.76 [GeV] • Cluster threshold ET= 7.44 [GeV] • Cluster size is one or two tower. L2gammaResult Contains: phi_bin,eta_bin, tower ET, and Cluster ET. ~1.2M events. ~50% Reversed Full Field. http://online.star.bnl.gov/L2gamma2007/l2gamma2007_bemc/ All runs after 8143* are in the reversed full field configuration.

  15. Preliminary QA of -trigger Data- BEMC Texas A&M Group Ahmed M. Hamed BNL 10-19-07

  16. Preliminary QA of -trigger Data- BSMD saturation Texas A&M Group Ahmed M. Hamed BNL 10-19-07

  17. Showers shape Analysis Real data vs. Single particle simulation Texas A&M Group Ahmed M. Hamed BNL 10-19-07 pp@2006 Shower shape is wider in real data than in simulation!

  18. Shower Shape Analysis Real data vs. pythia Texas A&M Group Ahmed M. Hamed BNL 10-19-07 Saturation parameters-Eta/Phi [700,70,10] • Pythia doesn’t reproduce the shower • shape even with saturation! • In phi-plane the shower shape is • closer to the real data than in eta.

  19. Shower Shape Analysis 0 vs. electron Texas A&M Group Ahmed M. Hamed BNL 10-19-07 Saturation parameters-Eta/Phi [700,70,10]

  20. Shower Shape Analysis 0 vs. electron Texas A&M Group Ahmed M. Hamed BNL 10-19-07

  21. Michael Betancourt

  22. 75% eff @ 75% rejection Single thrown γ and π0 Pibero Djawotho

  23. Summary Texas A&M Group Ahmed M. Hamed BNL 10-19-07 • -jet measurements are very promising tool for better understanding of • the medium. • Shower shape study is required for direct photons identification. • Promising study for transverse shower profile is undertaken. • Embedding request is still under processed.

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