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The STAR experiment -jet Measurements Table of Contents: Motivation STAR QM2005 && QM2006 Experimental setup Data and Analysis Method Transverse Shower Profile Results and Interpretation Summary Quark Matter 2008, February 4-10, Jaipur, India Texas A&M group Ahmed M. Hamed Jaipur 02-08-08 Energy loss Motivation Inclusive particle spectra at mid-rapidity: Heavy quarks suppress as much as light quarks in the medium. No observation confirms the expected color factors effect in energy loss . •Parton Distribution Function •Fragmentation Function •Intrinsic KT • Hard-Scattering •Shadowing •Partonic energy loss Forms of energy loss, s(T)? D0h/a(Z)->Dh/a(z,E) Jet-like azimuthal correlations Motivation Charged-Charged hadrons correlation Similar near side yield for jet-like yield per trigger in pp/AuAu The away-side in AuAu is strongly suppressed compared to pp and dAu. 4 < pT,trig< 6 GeV/c, 2< pT,assoc< pT,trig 0-5% STAR, PRL 90 (2003) 082302 STAR PRL 97 (2006) 162301 How Neutral-Charged correlation looks like? Motivation direct component Direct photons fragmentation component Bremsstrahlung No near side in gamma-jet correlation This contribution is negligible oGamma-charged hadrons correlation. Calibrated probe of the QGP – at LO. No Surface Bias Hard process Possible discriminator for quark/gluon jet at LO. How about neutral pions? Motivation In AuAu 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. Direct photons and 0 yields are similar in AuAu at ~10GeV Background sources of direct photons suppressed in medium. What are the expectations from previous measurements? STAR QM2005 AuAu@200GeV, Thomas Dietel Pythia Simulation shows no associated particles in the near-side of -jet correlations. Run2004 ( 30 ub-1 ) of AuAu@200GeV Suppression in both near- and away-side yield in central bin compared to peripheral bin. Correlations of charged particle show no modification of the associated near-side yield. Need /0 discrimination. STAR QM2006 pp@200GeV, S. Chattopadhyay Shower shape analysis is used for /0 discrimination. Reduction in near angle peak towards photon Bin. Effect is more prominent for larger Ettrigger . Away-side yield is reduced. What about AuAu? pp2005? Experimental setup Tracker detectors(slow), Trigger detectors(fast), and Calorimeters(fast). Measurements of hadrons production over a large solid angle. STAR BEMC can probe for further higher transverse energy. STAR Detector Experimental setup STAR BEMC -plane Electromagnetic transverse shower characteristics High energy core. Low energy halo. STAR BSMD can distinguish between /0 up to pt~26GeV/c Data and analysis method Run2007 Online: Trigger on cluster of one or two towers with Et>7.54GeV oData in Run2007( ~590 ub-1 ) Offline: Photon candidates “trigger particles” Trigger particle as of Et>8GeV in one or two adjacent towers. Trigger particle as of E>0.5GeV in one of BSMD strips. Charged particles veto as op>3GeV o<0.025 <0.025 of: Tracks “associated particles” Number of fit points Number of fit points/number of possible points >20. >0.52 Pt>3GeV/c Correlate photon candidates “triggers” with associated tracks Correct for tracking efficiency Subtract elliptic flow Use Transverse Shower Profile for /0 identification. Extract -jet away side yield Systematic study of: track veto cut, /0 identification, etc.. Transverse Shower Profile Transverse shower profile figure is here Results and interpretation Neutral-Charged hadrons correlation oNear side is suppressed in central bins compared to peripheral bins due to the increase of /0 ratio . oSuppression in near side increases with trigger energy. Results and interpretation Et trigger effect o(enriched sample)-jet correlation near-side is suppressed compared to 0-jet near-side. o0-jet correlation near-side increases with Et of the trigger particle o(enriched sample)-jet correlation near-side shows no dependence on Et of the trigger particle Results and interpretation Et trigger effect o(enriched sample)-jet correlation near-side is suppressed compared to 0-jet near-side. o0-jet correlation near-side increases with Et of the trigger particle o(enriched sample)-jet correlation near-side shows no dependence on trigger particle Et. o(enriched sample)-jet away-side is suppressed compared to 0-jet away-side at same centrality and Et. Results and interpretation Medium effect oClear away-side suppression in the medium. o(enriched sample)-jet correlation near-side shows no centrality dependence. Results and interpretation Extraction of 0 and -rich yields 1. Fit with 2-guassian and polynomial 2. Near-side yield=||<0.63, Away-side yield=|-|<0.63 Results and interpretation Comparison of 0 associated yields with charge associated yields in pp and dAu respectively Two different data sets: pp2006 and dAu2003 Complete different analysis techniques oGood agreement in the away- and near- side yields of the associated particles. Results and interpretation Comparison of 0 associated yields with charge associated yields in AuAu oGood agreement with previous STAR published analysis Results and interpretation Comparison of 0 associated yields with charge associated yields in AuAu oGood agreement with previous STAR published analysis in the common pt_assoc. bins. Results and interpretation Et dependence of 0 and -rich sample oNear-side yield of -rich sample shows no Et dependence. oNear-side yield of 0 shows slight increase with trigger Et. Results and interpretation Extraction of corrected away-side yields 1. R=(-rich-hadron yields/pi0-hadron yields)near-side 2. f= (pi0-hadron yields)away-side *R. 3. -corrected yields=[(-rich-hadron yields)away-side-f]/(1-R) oGood match with STAR results at QM2006 in the region of overlap. Results and interpretation corrected away-side yields in AuAu o away-side yield is smaller than 0 away-side yield. o away-side yield is harder than 0 away-side yield. Results and interpretation IAA Summary