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Energy Loss in Dense Media “Jet Quenching”

Energy Loss in Dense Media “Jet Quenching”. One of the first discoveries at RHIC!. PRL 88 (2002) 22301. PHENIX. Outline of My Talk. Introduction Quark Gluon Plasma at RHIC Jets and how they probe the QGP Jet quenching in heavy ion collisions pp baseline

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Energy Loss in Dense Media “Jet Quenching”

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  1. Energy Loss in Dense Media“Jet Quenching” One of the first discoveries at RHIC! PRL 88 (2002) 22301 PHENIX

  2. Outline of My Talk • Introduction • Quark Gluon Plasma at RHIC • Jets and how they probe the QGP • Jet quenching in heavy ion collisions • pp baseline • High pt particle suppression in Au-Au • d-Au control experiment • Suppression of jet-jet correlations • New experimental results • Medium modification of jet-correlations • Medium modifications of charm spectra • Summary & Outlook Axel Drees

  3. RHIC Relativistic Heavy Ion Collisions Quark-Gluon Plasma Critical point Color super- conductor Early Universe Temperature Hadron Gas “frozen Quarks” Color-flavor locking nuclei mbaryon or nucleon density Neutron Stars? The Phase Diagram of Nuclear Matter • QGP in Astrophysics • early universe: time < 106 seconds • possibly in the interior of neutron stars • Quest of heavy ion collisions • create QGP as transient state in heavy ion collisions • verify existence of QGP • study properties of QGP 170 MeV 1Gev/fm3 Overwhelming evidence for strongly interacting plasma produced at RHIC Axel Drees

  4. III. Jet Quenching I. Transverse Energy PHENIX 130 GeV Bjorken estimate: t0~ 0.3 fm dNg/dy ~ 1100 central 2% V2 PHENIX Huovinen et al II. Hydrodynamics Initial conditions: therm ~ 0.6 -1.0 fm/c ~15-25 GeV/fm3 Pt GeV/c Matter at RHIC has 15 GeV/fm3 ~15 GeV/fm3 Axel Drees

  5. Ideal Experiment to Probe the QGP • Rutherford experiment a atom discovery of nucleus SLAC electron scattering e  proton discovery of quarks QGP penetrating beam (jets or heavy particles) absorption or scattering pattern Nature needs to provide penetrating beams and the QGP in Au-Au collisions • QGP created in Au-Au collisions as transient state for 10 fm • penetrating beams created by parton scattering before QGP is formed • high transverse momentum particles  jets • Heavy particles  charm and bottom Axel Drees

  6. schematic view of jet production leading particle hadrons hadrons leading particle q q hadrons leading particle hadrons leading particle Jets: A Penetrating Probe for Dense Matter • What is a jet? • Incoming partons may carry large fraction x of beam momentum • These partons can scatter with large momentum transfer • Results in large pT of scattered partons • appears in laboratory as “jet” of particles • Jet production can be observed as • high pT leading particles • angular correlation • In a gold gold collision • Scattered partons travel through dense matter • Expected to loose a lot of their energy • Energy loss observed as • suppression of high pT leading particles • suppression of angular correlation • Depending on path length, i.e. centrality and angle to reaction plane reaction plane Axel Drees

  7. Jet production measured indirectly by transverse momentum (pT) spectrum Identified particles (p0) Charged particles (h = p, K, p, .. ) At RHIC energies different mechanisms are responsible for different regions of particle production Thermally produced “soft” particles “hard” particles from jet production Hard component can be calculated with QCD Data agrees with QCD calculation “calibrated” reference hard Particle Spectra from p-p Collisions p0 from p-p collisions QCD calculation soft Axel Drees

  8. Participants Scaling from p-p to Heavy Ion Collisions • Hard-scattering processes in p-p • quarks and gluons are point-like objects • small probability for scattering in p-p • p-p independent superposition of partons • Minimum bias A-A collision • assume small medium effects on parton density • superposition of independent p,n collisions • collision probability increases by A2 • cross section scales by number of binary collisions • Impact parameter selected A-A collisions • superposition of p,n collisions among participants • calculable analytically by nuclear overlap integral • or by MC simulation of geometry “Glauber Model” Axel Drees

  9. g q g q Binary Scaling in Au-Au tested with Direct Photons • pp collisions: • qg-Compton scattering • Direct g production described by NLO pQCD • Au-Au collisions: • Direct g rates scale with Nbinary • Similar scaling observed for charm quark production Hard processes in Au-Au scale with Nbinary Axel Drees

  10. Suppression of p0 in Central AuAu Collisions PRL 91 (2003) 72301 Nuclear modification factor: PHENIX PHENIX preliminary High pT suppressed by factor ~ 5 pp to central AuAu and peripheral to central Au-Au Axel Drees

  11. deuteron gold collision gold-gold collision Control Experiment with d-Au • Final state effect “jet quenching” • Medium created in d-Au has small volume • Jets easily penetrate short distance • No suppression of jet yield expected in d-Au • Initial state saturation effect • Gluon density saturated in incoming gold nucleus • Deuteron shows no or little saturation • Expect suppression of jet yield, but with reduced magnitude Final state effect: no suppression Initial state effect: suppression Axel Drees

  12. Suppression at Parton Level • No suppression for direct photons • Hadron suppression persists up to >20 GeV jets • Common suppression for p0 and h; it is at partonic level • Typical model calculation: e > 15 GeV/fm3; dNg/dy > 1100 Hot opaque partonic medium: e > 15 GeV/fm3 Axel Drees

  13. Convolute jet absorption or energy loss with nuclear geometry (many publications) Centrality Dependence of Suppression • Hard region: pT > 7 GeV/c • Suppression depends on centrality but not on pT • Characteristic features of jet fragmentation independent of centrality • pQCD spectral shape • h/p0 constant • xT scaling Centrality dependence characteristic for jet absorption in extremely opaque medium! Insensitive to details of energy loss mechanism Axel Drees

  14. p+p Trigger particle with high pT > pT cut 1 yield/trigger 0 Df to all other particles with pT > pT cut-2  /2  0 Au+Au yield/trigger elliptic flow random background 0  /2  0 statistical background subtraction Au+Au ??? Au-Au yield/trigger suppression? 0  /2  0 Azimuthal Correlations from Jets pp jet+jet STAR Jet correlations in Au-Au via statistical background subtraction Axel Drees

  15. Disappearance of the “Away-Side” Jet Integrate yields in some f window on near and away side pedestal and flow subtracted trigger 6 <pt< 8 GeV partner 2 < pt < 6 GeV Near-side: p+p, d+Au, Au+Au similar Back-to-back: Au+Au strongly suppressed relative to p+p and d+Au Suppression of the away side jet in central Au+Au Axel Drees

  16. Suppression of Back-to-Back Pairs Jet correlation strength: Near side Compared to jet absorption model (J.Jia et al.) Away side Away side jets are suppressed consistent with jet absorption in opaque medium “Mono jets” point outward Axel Drees

  17. Surviving “Di jets” tangential “Mono jets” point outward ~factor 5 Decreased surface/volume Qualitatively consistent with surface emission Remaining Jets from Matter Surface 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV D. Magestro, QM2005 STAR Preliminary Axel Drees

  18. partner > 1 GeV Trigger > 2.5 GeV Where Does the Energy Go? Axel Drees

  19. Modification of Jet Shape at Lower pT Near side Away side PHENIX preliminary Can jet shape be related to properties of matter? Axel Drees

  20. Wake effect or “sonic boom” Shuryak et al. Theoretical Speculation: Sound velocity? Dielectric Constant?Jet Tomography will be power tool to probe matter! • Energy loss of jet results in conical shock wave in strongly interacting plasma • Hydrodynamic mach cone? • Longitudinal modes ? • Cherenkov radiation ? • Momentum conservation “multiple scattering” with meduium • Medium evolution of radiated gluons Axel Drees

  21. e,m X p D p p0 e g e How opaque is the medium? Check Charm Production! p+p • Signal: • Background: • Default PYTHIA parameterization • PDF – CTEQ5L; mC = 1.25 GeV; mB = 4.1 GeV • <kT> = 1.5 GeV; K = 3.5 • Parameterization tuned to describe s < 63 GeV p+N world data • Spectral shape is “harder” than PYTHIA expectation background subtracted electron spectrum pp PHENIX preliminary Axel Drees

  22. Open Charm in Au+Au at sNN=200 GeV • Total yield scales with number of binary collisions No indication of strong medium modification of charm production Axel Drees

  23. Heavy Quark Energy Loss: Nuclear Modification Factor • Strong modification of the spectral shape • Suppression by factor 2-5, similar to pion suppression • Large bottom contribution above 4 GeV? Production of charm scales like hard process Spectral shape modified while propagating in medium Axel Drees

  24. z y x   Elliptic Flow: A Collective Effect dn/d ~ 1 + 2v2(pT)cos (2 ) + ... • Initial spatial anisotropy is converted • into momentum anisotropy Axel Drees

  25. Greco,Ko,Rapp: PLB595(2004)202 Charm Quarks flow with light quarks • Charm flows, strength ~ 60% of light quarks (p0) • Drop of the flow strength at high pT due to b-quark contribution? • The data favor the model that charm quark itself flows at low pT. High parton density and strong coupling in the matter Axel Drees

  26. Summary & Outlook Strongly interacting QGP produced at RHICState of unprecedented energy density ~ 15 GeV/fm3Opaque to colored “hard” probes, jets and heavy flavor Hard probes will be critical to study properties of QGP On tape; analysis ongoing 2004 4x larger Au-Au data sample in 2006 2001 2002 Factor 10 luminosity increase with electron cooling after 2010 Discovery of jet quenching Most data seen today Axel Drees

  27. Backup Slides Axel Drees

  28. pQCD direct g + jet quenching PHENIX Preliminary AuAu 200 GeV 0-10% pQCD direct g g q g q Outlook into the “Away” Future g-jet: the golden channel for jet tomography Quark gluon Compton scattering: g-energy fixes jet energy g & Jet direction fix kinematics measure DE as function of: E, “L”, flavor 70% of photons are prompt photons Promising measurement at RHIC: every low cross section; pT< 8-10 GeV on tape luminosity and detector upgrades: extend range to pT~25 GeV and |y|<3 Axel Drees

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