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Hard Probes and Heavy Flavor from STAR

Hard Probes and Heavy Flavor from STAR. Saskia Mioduszewski for the STAR Collaboration Texas A&M University Rencontres de Moriond: QCD and High Energy Interactions 14 March, 2008. Why Hard Probes?. Only photons decouple from medium upon creation

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Hard Probes and Heavy Flavor from STAR

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  1. Hard Probes and Heavy Flavor from STAR Saskia Mioduszewski for the STAR Collaboration Texas A&M University Rencontres de Moriond: QCD and High Energy Interactions 14 March, 2008

  2. Why Hard Probes? • Only photons decouple from medium upon creation • Large-mass quarks provide particularly good probe of medium produced • Created early in the collision • mc ~ 1.3 GeV, mb ~ 4.8 GeV >> Tc, LQCD less affected than light quarks • Perhaps more direct connection to transport properties of medium What Questions Can be Addressed via Hard Probes? • g-jet : true (modified) fragmentation function • Open Charm/Beauty: energy loss mechanism, degree of thermalization • Quarkonium: deconfinement (dissociation in QGP), degree of thermalization

  3. STAR PRL, 98, 192301 (2007) One of the most surprising results from RHIC • Heavy flavor suppression as large as for light quarks • No dependence of energy loss on flavor • Do we understand energy loss mechanism? • Where is Beauty contribution?

  4. Anti-particle/particle Quark vs. Gluon Energy Loss Baryon & meson RAA Mechanism of energy loss : Medium-induced gluon radiation Effect of color charge: Factor 9/4 Color effects not observed up to pT ~ 12 GeV/c - Not sensitive? - In-medium conversions, qg? (W. Liu, R.J. Fries, arXiv:0801.0453) - Energy loss mechanism not understood Theory: X.-N. Wang, PRC 70 (2004) 031901 Data: PRL 97 (2006) 152301 PLB 655 (2007) 104

  5. From Single-Particle to 2-Particle Correlations Di-jets (hadron-hadron correlations) Single inclusive hadrons Suppression quantified by IAA = Jet-assoc. YieldAA/Jet-assoc. Yieldpp Hadrons associated with high-pT trigger particle  More differential probe of energy loss Surface bias reduced, but not removed Suppression quantified by RAA = YieldAA/(Yieldpp *<Nbinary>pp) Single particle is leading hadron of jet  Probe of density of medium, but Strong surface bias for “trigger” particle Trigger

  6. Escaping Jet “Near Side” q g Lost Jet “Far Side” Trigger Biases Di-jets (hadron-hadron correlations) Single inclusive hadrons Renk and Eskola, hep-ph/0610059 Renk and Eskola, hep-ph/0610059 Trigger particle Trigger particle • Photon-jet measurement is, in principle, sensitive to full medium • True measure of the Energy (no energy loss for direct photon)

  7. -Jet: “Golden Probe” of QCD Energy Loss Wang et al., Phys.Rev.Lett. 77 (1996) 231-234   q •  emerges unscathed from the medium - This probe is valuable for comparison with di-hadron correlations - Full reconstructed kinematics: real fragmentation function D(z) g q QCD analog of Compton Scattering h

  8. -jet yield Away-side hadrons Jet Suppression measured via direct photon trigger T. Renk, PRC74, 034906 Theoretical calculation showing sensitivity to medium 8

  9. First measure of away-side IAA for g-h A. Hamed, QM2008 Ejet = E = E trig Good agreement between theory and measurement T. Renk and K. Eskola PRC75:054910,2007 Suppression similar level to inclusives in central collisions

  10. Away-side Yields Relative to Peripheral Au+Au A. Hamed, QM2008 Peripheral Au+Au ~ p+p = vacuum Icp of -jet exhibits same suppression on the away-side yield per trigger of the associated particles (3-8GeV/c). 10

  11. STAR PRL, 98, 192301 (2007) One of the most surprising results from RHIC • Heavy flavor suppression as large as for light quarks • No dependence of energy loss on flavor • Do we understand energy loss mechanism? • Where is Beauty contribution?

  12. + K- e- D0 e like-sign e-K pairs D*0 B- b b c essentially from B decays only 75% from charm 25% from beauty c B+ D0 c g g g e –D0 correlation with g g g - c K+ Electron-tagged correlations to obtain bottom contribution • Experimental approach - non-photonic electrons from semi-leptonic charm decays are used to trigger on c-c̅, b-b̅ pairs • back-2-back D0 mesons are reconstructed via their hadronic decay channel (probe)‏ • Underlying production mechanism can be identified using second charm particle A. Mischke, QM 2008 heavy quark production 0  flavor creation gluon splitting/fragmentation

  13. e-h Heavy quark production in p+p collisions - the B contribution to non-photonic electrons is ~50% at pT~5 GeV/c, based on e-h and e-D correlations e-D0 correlation agree with e-h results A. Mischke, S. Sakai, G. Wang, QM2008

  14. J/Y Suppression We expect a suppression of bound states due to color screening in the Quark Gluon Plasma.(Matsui & Satz, 1986) Data from SPS, showing J/Y suppression • Charm cross-section larger at RHIC than SPS – ~ 20 cc pairs produced per collision • We have evidence that charm may be partially thermalized at RHIC  recombination of cc pairs to regenerate J/Y ? • Or sequential melting of charmonium (Karsch, Kharzeev, Satz)

  15. Heavy Quarkonium Production (and Survival) Two Component Approach: X. Zhao and R. Rapp, hep-ph/07122407 Ads/CFT Calculation of Survival J/Y Production in p+p collisions Most models expect a decrease in RAA as function of pT H. Liu, K. Rajagopal and U.A. Wiedemann PRL 98, 182301(2007) and hep-ph/0607062 Z. Tang, QM2008 Next step the  - almost there Z. Tang Session XVII, D. Das Session XXII

  16. Heavy Quarkonium Production (and Survival) J/Y in Cu+Cu Collisions at RHIC Z. Tang, QM2008 • Data consistent with no suppression at high pT: RAA(pT > 5 GeV/c) = 0.9 ± 0.2 • While at Low-pT RAA: 0.5—0.6 (PHENIX)‏ • Indicates RAA increase from low pT to high pT • Most models expect a decrease RAA at high pT(not including bottom decays): Two Component Approach: X. Zhao and R. Rapp, hep-ph/07122407 AdS/CFT: H. Liu, K. Rajagopal and U.A. Wiedemann, PRL 98, 182301(2007) and hep-ph/0607062 Contribution from beauty decays - better agreement

  17. Conclusions • Surprise at RHIC: heavy-quark energy loss does not follow expectation – Do we really understand energy loss mechanism? • Exploring di-jet and photon-jet measurements to constrain energy loss mechanism • Beauty contribution to heavy flavor measurements is ~50% at pT~5 GeV/c, indicating that bottom must be suppressed as well • J/Y not suppressed at high pT, contrary to expectation from theoretical calculation if no contribution from Beauty decays • Need direct measure of Charm/Beauty up to high pT – will be possible with planned upgrades

  18. Extra Slides

  19. Elliptic flow v2 – NPE from HF decays PHENIX Run4 PRL, 98, 172301 (2007) Non-zero elliptic flow for electron from heavy flavor decays → indicatesnon-zero D v2,partonic level collective motion. Strongly interact with the dense medium at early stage of HI collisions. Light flavor thermalization.

  20. Associated hadron spectra with leading J/ J/Ψ – hadron correlations in p+p 1) no near side correlation 2) strong near side correlation Z. Tang, QM2008 No near side correlation seen! Away side:consistent with leading charged hadron correlations Near side:consistent with no associated hadron production BJ/ not a dominant contributor to inclusive J/

  21. 200 GeV Au+Au & d+Au 1 _dN_ Ntrigd(Df ) STAR Preliminary Au+Au d+Au 3 2 1 0 -2 -1 2 0 1 3 4 5 Df Triggering on Di-Jets T1: pT>5 GeV/c, T2: pT>4 GeV/c, A: pT>1.5 GeV/c • Di-jets are suppressed. • Once select di-jets, away-side associated particles NOT suppressed. • Shapes of near- and away-sides similar. • Central Au+Au ~ d+Au. “jet-axis” trigger (T2) primary trigger (T1) O. Barannikova, QM2008 No energy loss for triggered di-jets! Tangential di-jets (or punch-through without interactions).

  22. D* - jet correlation e-h e-D0 correlation agree with e-h results Heavy quark production in p+p collisions The B contribution to non-photonic electrons is ~50% at pT~5 GeV/c, based on e-h and e-D correlations A. Mischke, S. Sakai, G. Wang, QM2008

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