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Parton Energy Loss and Jet Tomography: Probing the "Perfect Liquid" at RHIC

Parton Energy Loss and Jet Tomography: Probing the "Perfect Liquid" at RHIC. Why Jets? Where We’ve Been R AA , x T scaling, direct photons Setting the foundation Where We Are Now New colliding systems and energies Cones and wakes Where We’re Going Higher p T

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Parton Energy Loss and Jet Tomography: Probing the "Perfect Liquid" at RHIC

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  1. Parton Energy Loss and Jet Tomography: Probing the "Perfect Liquid" at RHIC • Why Jets? • Where We’ve Been • RAA, xT scaling, direct photons • Setting the foundation • Where We Are Now • New colliding systems and energies • Cones and wakes • Where We’re Going • Higher pT • Untangling Jets and the Medium John Lajoie, Iowa State University Focus on observables, not chronology… Second DNP/JPS Joint Meeting, Maui

  2. leading particle q q leading particle Jets: Partonic Probes Produced early in the collision (t<1fm/c) Evolution is sensitive to QCD medium, primarily through energy loss Not possible to observe jets directly in RHI collisions – large overall particle density Identify jets through leading particles and correlations. “Jet Tomography” – probe the intervening QCD matter… Second DNP/JPS Joint Meeting, Maui

  3. Jet Quenching: In The Beginning Final Data Preliminary Data • Suppression in AuAu data as a function of centrality • Enhancement in d+Au data (Cronin effect) Second DNP/JPS Joint Meeting, Maui

  4. xT Scaling PRC 69, 034910 (2004) PRC 69, 034910 (2004) Deviation from xT scaling occurs at pT ~ 2 GeV/c Second DNP/JPS Joint Meeting, Maui

  5. xT Scaling in AuAu Collisions Does xT scaling work in AuAu collisions – do we really see hard scattering? PRC 69, 034910 (2004) Assuming structure and fragmentation functions scale, should get same n. Power law exponent derived by dividing 130 and 200 GeV data. Something special about charged hadrons in central collisions? Second DNP/JPS Joint Meeting, Maui

  6. Protons vs. Pions Protons and antiprotons in AuAu collisions are weird! PRL 91, 172301 (2003) Excess of protons compared to pions at high-pT Wait a minute – don’t these particle come from jet fragmentation? Second DNP/JPS Joint Meeting, Maui

  7. Direct Photons in AuAu It’s “easy” to measure the direct photons because the p0’s are heavily suppressed! Comparison with pQCD calculation agrees with measured multiplicity – we understand the initial state. (see talks by K. Okada, H. Torii, T. Sakaguchi this session) Second DNP/JPS Joint Meeting, Maui

  8. CARTOON flow+jet flow N F Two-Particle Correlations • Study the effect of the medium through the correlation of particles within the jets. • “Near-Side” correlations are between particles from the same jet • Correlation width related to mean fragmentation momentum (jT) • “Away-Side” correlations are between particles from different jets • Correlation width sensitive to jet acoplanarity (kT) • Both could be sensitive to medium effects (energy loss, radiation) • Flow (v2) is a background! assoc. particle trigger particle Second DNP/JPS Joint Meeting, Maui

  9. STAR, Phys Rev Lett 91, 072304 Jet Quenching in Correlations “Disappearance” of the away-side jet correlation in central AuAu collisions! Second DNP/JPS Joint Meeting, Maui

  10. 2σ syst 1σ syst Jet Structure vs. Centrality • Away-side correlations in AuAu display unusual shape! • Indication of shock wave? • hep-ph/0411315 • nucl-th/0506013 • If so this may measure the speed of sound in the medium • Dramatic scattering of jet axis? • “Bent Jet” PHENIX Preliminary Second DNP/JPS Joint Meeting, Maui

  11. |Eta|<1.0 |Eta|<0.35 STAR/PHENIX Comparison trigger pT =2.5-4 GeV/c, associated pT =1.0-2.5 GeV/c PHENIX Preliminary STAR Preliminary (James Ulery, QM05) Second DNP/JPS Joint Meeting, Maui

  12. Away-Side Shape at SPS(!) • CERES data at much lower but similar trigger and associated pT ranges • higher xT than RHIC data • Correlation is flat at far angles • same structure as seen at RHIC! (D. Miskoweic, QM05) Second DNP/JPS Joint Meeting, Maui

  13. assoc assoc D D trigg trigg D assoc Quantifying the Away-Side Parameterize the away-side shape as double Gaussians that are offset symmetrically aroundDf = pby fit parameter D. Could be a “bent” jet or a Mach/ Cerenkov cone … (see talk by P. Constantin this session) Second DNP/JPS Joint Meeting, Maui

  14. Size/Energy Dependence Au+Au @ 62.4 GeV h-h 2.5-4 x 1-2.5 GeV/c PHENIX Preliminary The splitting parameter is independent of system and energy. Second DNP/JPS Joint Meeting, Maui

  15. d+Au min-bias near near Df2 Dφ2=φ2-φtrig Medium Medium away away mach cone Df1 pTtrig=3-4, pTassoc=1-2 GeV/c 2-particle corr, bg, v2 subtracted Au+Au 10% Df2 Dφ2=φ2-φtrig deflected jets Df1 Dφ1=φ1-φtrig Three Particle Correlations d+Au and Au+Au elongated along diagonal: kT effect, and deflected jets? Distinctive features of conical flow are not seen in present data with these pT windows. (James Ulery, QM05) Second DNP/JPS Joint Meeting, Maui

  16. After Harmonic Extinction: PHENIX Preliminary Mach cone Simulation Data indicates apparent cone structure for away-side jet! Three Particles a-la PHENIX 10%<cent<20% PHENIX Preliminary Jet only Flow+Jet (N. Ajitanand, QM05) Second DNP/JPS Joint Meeting, Maui

  17. Higher pT Is Good! • The proton to pion ratio appears to return to “normal” at high pT. • Higher pT may be essential to separate effects such as recombination from jet energy loss for charged hadrons • Should be able to develop a consistent picture for p0 and charged • In the most central collisions, “jet physics” may be most cleanly done for pT>4-5 GeV/c PRC 69, 034910 (2004) Second DNP/JPS Joint Meeting, Maui

  18. STAR Preliminary 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV Emergence of Jets at High pT STAR Preliminary pT(assoc)> 2 GeV/c PHENIX Preliminary (D. Majestro, QM05) Above ~7 GeV/c trigger the away-side jet reappears. Very clear near and away-side peaks even in central AuAu! (H. Pei, QM05) Second DNP/JPS Joint Meeting, Maui

  19. 8 < pT(trig) < 15 GeV/c Away-Side Jet Widths STAR Preliminary PHENIX Preliminary Hua Pei (QM05 Poster) Widths do not change between p+p and Au+Au? Second DNP/JPS Joint Meeting, Maui

  20. a L1 L2 L1 c L2 b L1 L2 Jet Widths: Implications • Tangential jets • We see only jets produced on the surface of the interacting matter? • Jets which “see” any significant part of the medium are destroyed • Consistent with inclusive RAA? A. Dainese et al, EJPC 38 (2005) 461 Second DNP/JPS Joint Meeting, Maui

  21. 8 < pT(trig) < 15 GeV/c Associated Yields at High-pT • Yields decrease smoothly with centrality • IAA (with d+Au denominator) suppression!! • Similar suppression between the different pT ranges. (IAA plot by Nathan Grau) Second DNP/JPS Joint Meeting, Maui

  22. Picture of High-pT Jets Very different centrality dependence of these observables! Are these results reconcilable in an energy loss picture? Second DNP/JPS Joint Meeting, Maui

  23. Conclusions • Jets at intermediate trigger pT • Clear broadening of away-side jet with increasing centrality • Non-Gaussian away-side correlations with “dip” structure evolving as a function of centrality • Cone or “bent jet”? Stay tuned…. • Jets at high trigger pT • Jet correlations still visible in central AuAu collisions at high trigger/associated pT • Correlation widths unmodified as a function of centrality • Away-side peak suppressed with increasing centrality • Correlation widths, strength and RAA all show different centrality dependence • Can we reconcile these observables? Second DNP/JPS Joint Meeting, Maui

  24. Future Prospects • The future promises a wealth of new measurements that will further elucidate the interaction of jets with the medium – true “Jet Tomography”! • Three particle correlations • “Bent Jets” or Cone? • Reaction plane dependence of correlations • Further probe the geometry dependence • Are CuCu and AuAu really the same at the same Npart? • Gamma-Jet correlations • Energy-calibrated probe! • Heavy flavor • LPM effect? Does heavy flavor lose energy in the same way? Second DNP/JPS Joint Meeting, Maui

  25. BACKUP Second DNP/JPS Joint Meeting, Maui

  26. Correlations: Low To High pT hadron-hadron correlations Green/blue lines indicate flow uncertainty. Most peripheral collisions: Jet is seen for all pT Onset of away-side jet modification in semi-peripheral collisions. Flattening and dip structure at low pT and at high centrality. Second DNP/JPS Joint Meeting, Maui

  27. Near Side Broadening PHENIX Preliminary In the near angle – systematic trend of broadening as a function of centrality. How does this trend persist at different pT? Second DNP/JPS Joint Meeting, Maui

  28. Near-Side at High pT At higher pT, no increase with centrality Consistent with the picture of production at the corona. Is there a smooth change in the near-side broadening between intermediate and high pT? Second DNP/JPS Joint Meeting, Maui

  29. CARTOON flow+jet flow N F ID’d Particle Correlations trigger “near side”  < 90° jet partner “away side”  > 90° opposing jet PRC 71, 051902(R) (2005) Second DNP/JPS Joint Meeting, Maui

  30. Reaction Plane Dependence Red– 6 Green – 5 Blue – 4 Light Blue – 2Pink – 1 Black - Integral Require the trigger particle within a given RP orientation Flow varies in a particular way J. Bielcikova et al Phys. Rev. C69:021901, 2004 Second DNP/JPS Joint Meeting, Maui

  31. Reaction Plane at High pT Hua Pei (QM05 Poster) Second DNP/JPS Joint Meeting, Maui

  32. Near-Side RP Dependence Near-side widths are flat as a function of reaction plane – still consistent with production at the corona. Second DNP/JPS Joint Meeting, Maui

  33. g Hadrons Photon Tagged Jets • High statistics datasets in CuCu and AuAu allow for the correlation of direct photons with partner jets. • The photon escapes the medium unmodified. • “Calibrates” the energy of the jet • Reduced Bias • Jet correlations through leading particles biases you to high <z> as well as the “corona” of the collision volume • Again, high pT essential • High signal/background for direct photons • Jet particles free from lower-pT effects (recombination, flow) Second DNP/JPS Joint Meeting, Maui

  34. Hard Scattering? • How do we know that we have hard scattering in the first place? • xT scaling of invariant cross-section: • The power due to higher order effects • Measured cross sections should scale with xT Second DNP/JPS Joint Meeting, Maui

  35. Far Side Near Side Another View… PHENIX Preliminary Second DNP/JPS Joint Meeting, Maui

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