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 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

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? STAR PRL, 98, 192301 (2007)

Quark vs. Gluon Energy Loss Baryon & meson RAA Mechanism of energy loss : Medium-induced gluon radiation Effect of color charge: Anti-particle/particle 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

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

Di-jets (hadron-hadron correlations) Single inclusive hadrons Trigger Biases Di-jets (hadron-hadron correlations) Single inclusive hadrons Escaping Jet “Near Side” Lost Jet “Far Side” 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) g q

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

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

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

Peripheral Au+Au ~ p+p = vacuum 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

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? STAR PRL, 98, 192301 (2007)

Electron-tagged correlations to obtain bottom contribution K- b b B- D*0 D0 + e e- B+ - K+ D0 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 essentially from B decays only like-sign e-K pairs e –D0 correlation with 75% from charm 25% from beauty A. Mischke, QM 2008 heavy quark production g c c c c g 0  flavor creation gluon splitting/fragmentation

Heavy quark production in p+p collisions e-h e-D0 correlation agree with e-h results - 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

Data from SPS, showing 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)

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

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

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

Extra Slides

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

J/Ψ – hadron correlations in p+p Associated hadron spectra with leading J/ 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/

No energy loss for triggered di-jets! Triggering on Di-Jets T1: pT>5 GeV/c, T2: pT>4 GeV/c, A: pT>1.5 GeV/c Au+Au d+Au Df -1 -2 1 2 3 4 5 1 _dN_ Ntrig d(Df ) STAR Preliminary 200 GeV Au+Au & d+Au “jet-axis” trigger (T2) primary trigger (T1) 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. O. Barannikova, QM2008 No energy loss for triggered di-jets! Tangential di-jets (or punch-through without interactions).

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