1 Probing the medium with photons Outline: oMotivation oExperiment oResults oConclusion oIntroduction LBNL 21-05-07 Saskia Mioduszewski Ahmed Hamed.
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1 Probing the medium with photons Outline: oMotivation oExperiment oResults oConclusion oIntroduction LBNL 21-05-07 Saskia Mioduszewski Ahmed Hamed
2 Probing the medium High-p T Spectra I – Light quarks and gluons The suppression of 0, s and , s is very similar. suppression occurs at the parton level. The binary scaling of direct photons is strong evidence that suppression is not an initial state effect. Mid-rapidity Statistical Method LBNL 21-05-07 s C x qL ^ 2 “Static medium” Gluons dominance at mid-rapidity at RHIC energy. Photons PHENIX, QM05
3 QCD is flavor independent, but heavy quarks at same p T are moving much slower than light quarks. Expected “dead-cone” with no induced gluon radiation. Non photonic electrons-Charm and Beauty LBNL 21-05-07 Probing the medium High-p T Spectra II– Heavy quarks and gluons osingle-particle suppression does not constrain the mechanism of energy loss. osingle-particle suppression in AuAu is strong evidence for the hot and dense medium formation. nucl-ex/0607012
4 LBNL 21-05-07 Baryons and Mesons Clear meson-baryon yield differences at intermediate p T. Probing the medium High-p T Spectra III– quarks and gluons No reduction is observed in the baryon/meson ratio as expected in the gluon dominance picture. Calibrated probe of the QGP is needed for better understanding of energy loss. STAR QM05 and nucl-ex/0601042
5 LBNL 21-05-07 ? 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 Probing the medium Jet-like azimuthal correlations LBNL 21-05-07 Surface bias for the trigger particle. Trigger particle with no surface bias is required for better quantitative measurements of the away-side modifications. Charged hadrons
6 Introduction Summary LBNL 21-05-07 Better understanding for the energy loss mechanism! Elliptic flow. oDirect Photons: Gamma-charged hadrons correlation. 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: Challengeable measurements! Doesn’t couple to the medium. QGP thermal photons. Test for binary scaling for hard process.
7 Motivation LO Direct photons Bremsstrahlung fragmentation component direct component Decay photons hard: thermal: schematic view Calibrated probe of the QGP – at LO. No Surface Bias Hard process single-particle suppression does not effectively constrain detailed energy-loss pictures. LBNL 21-05-07 Possible candidate for quark/gluon jet discrimination at LO. oGamma-charged hadrons correlation.
8 Experiment STAR Detector Tracker detectors(slow), Trigger detectors(fast), and Calorimeters(fast). LBNL 21-05-07 Measurements of hadrons production over a large solid angle. STAR BEMC can probe for further higher transverse energy.
9 Experiment STAR BEMC Cross-section in LBNL 21-05-07 o120 modules. o4800 channels oSMDs: 36000 channels oPreShower: 4800 channels oLead-scintillator detector. oSampling calorimeter. oProjective towers. Cross-section in BEMC face is ~2.2m away from the point of interaction at =0. West side 0< <1
10 Experiment Electromagnetic Shower LBNL 21-05-07 -plane -plane High energy core. Low energy halo. Electromagnetic transverse shower characteristics
11 Inclusive - jet in Au+Au at s=200GeV Thomas Dietel Quark Matter 2005 Results QM 2005 LBNL 21-05-07 SIMULATION (pp) The background is higher for central events. Away-side decreases with increasing centrality. Decrease in near-side due to the increased fraction of prompt photons. Need / 0 discrimination. STAR Preliminary Simulation shows no associated particles in -charged correlation.
12 Results QM 2006 S. Chattopadhyay Quark Matter 2006 LBNL 21-05-07 Reduction in near angle peak towards photon Bin. Effect is more prominent for larger E t trigger. Away-side yield is reduced. pp at s=200GeV STAR Preliminary
13 Results Transverse Shower Profile LBNL 21-05-07 Clear structure for the two showers in and 0 at moderate energy. 0 shower at high energy is still wider than the single photon shower. Could be used to distinguish 0 / Clear sensitivity to the halo region.
14 cucu 0-10% Et_trg>12GeV Et_trg>6GeV /c (rad) /c 00 Results Raw correlation function LBNL 21-05-07 Preliminary Similar Away-side for 0 and Reduction in the near-side for compared to 0. Reduction is more noticeable at higher Et_trg and also at higher centrality bins. d 1 N trg dN ( ) Y-axis:
15 Conclusion LBNL 21-05-07 -charged hadrons correlation is 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. Comparison with the previous study of transverse shower profile is necessary.
16 Thank you all Thanks to Texas A&M nuclear physics group. Thanks to all STAR Collaborators