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Experimental Aspects of Heavy Ion Physics

Experimental Aspects of Heavy Ion Physics. Introduction Quark Gluon Plasma produced at RHIC Probing the QGP with hard scattering Jet quenching: energy loss in dense media pp baseline High p T particle suppression in Au-Au d-Au control experiment Suppression of jet-jet correlations

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Experimental Aspects of Heavy Ion Physics

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  1. Experimental Aspects of Heavy Ion Physics • Introduction • Quark Gluon Plasma produced at RHIC • Probing the QGP with hard scattering • Jet quenching: energy loss in dense media • 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 • Inmedium J/ suppression • Summary & Outlook

  2. 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 < 10-6 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

  3. 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 int~15 GeV/fm3 int ~ 100x enucleus ~ 10x ecritical Axel Drees

  4. g q g q First Hints for Thermal Radiation • PHENIX preliminary • Direct photon measurement at low pT from low-mass electron pair analysis • Below 3 GeV yield well above pQCD calculation • Data consistent with pQCD + thermal radiation thermal radiation pQCD L.E.Gordon and W. Vogelsang Phys. Rev. D48, 3136 (1993) D. d’Enterria, D. Perresounko nucl-th/0503054 Tint ~ 500-600 MeV 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 • Penetrating beams created by parton scattering before QGP is formed • High transverse momentum particles  jets • Heavy particles  open and hidden charm or bottom • Probe QGP created in Au-Au collisions as transient state after ~ 1 fm 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 • Jets: • Scattering of incoming partons with large fraction x of beam momentum • Appear in laboratory as “jet” of particles with large momenta • Indirect observation of jets: • high pT “leading” particles • Azimuthal 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 Example identified particles (p0) 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. 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

  10. 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

  11. g q g q 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 M. Gyulassy et al. dNg/dy > 1100 Hot opaque partonic medium: e > 15 GeV/fm3 Axel Drees

  12. Short path length to surface  jet survives Centrality dependence ≡ nuclear geometry (many publications) Centrality Dependence of Suppression • Hard region: above pT > 5 GeV/c the suppression depends on centrality but not on pT ! Centrality dependence characteristic for jet absorption in extremely opaque medium! Mostly insensitive to details of energy loss mechanism! Axel Drees

  13. 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

  14. 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

  15. 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

  16. 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

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

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

  19. 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? • J. Casalderray, E. Shuryak, D. Teaney, hep-ph/0411315 • Longitudinal modes ? • H. Stöcker, Nucl. Phys. A750, (2005) 121 • J. Ruppert, B. Müller , Phys. Lett. B618 (2005) 123 • Cherenkov radiation ? • I. Dremin (1979,2005) • A. Majumder and X.-N. Wang (2005) • Momentum conservation “multiple scattering” with medium • Borghini, Wiedemann, hep-ph/0506218 • Medium evolution of radiated gluons • S. Pal and S. Pratt, Phys. Lett. B574 (2003), 21-26 Axel Drees

  20. e,m X p D p p0 e g e Signal yield / Ncoll Open Charm in Au+Au at sNN=200 GeV • Inclusive electron production • Signal: • Background: Signal electrons Charm yield scales with Ncoll as expected for a hard production process Axel Drees

  21. (1)-(3) U.Wiedemann et al. (4) M. Guylassy et al. Heavy Quark Energy Loss • Issues for theoretical models • Consistentcy with pion suppression • Expect large bottom contribution above 4 GeV? Charm spectral shape modified while propagating in medium Axel Drees

  22. Greco,Ko,Rapp: PLB595(2004)202 z y x   Charm Quarks flow with light quarks Elliptic Flow: A Collective Effect • Charm flows, strength ~ 60% of light quarks (p0) • The data favor the model that charm quark itself flows at low pT. High parton density and strong coupling in the matter Axel Drees

  23. dAu mm 200 GeV/c AuAu mm 200 GeV/c CuCu mm 200 GeV/c AuAu ee 200 GeV/c CuCu ee 200 GeV/c Recent results on J/y Production • Cold nuclear matter breaks J/y; expect suppression up to factor ~2! (suppression at CERN SPS ~1.4 larger than expectation) • J/y suppressed by factor of ~ 3 compared to binary scaling, similar to SPS results • Old idea: color screening in QGP dissolves charmonium! J/ suppression in heavy ion collisions tentatively beyond cold nuclear matter effects (?) very similar to observations at CERN SPS Axel Drees

  24. Comparison to Predictions of J/y Production • Models with only cold nuclear matter effects don’t quite have enough suppression • Models with color screening or comovers and have too much suppression • Models with statistical recombination at freezeout are in reasonable agreement with the data Matter seems so dense that J/y melts and regenerates!If so J/y must flow, test by measuring v2! Axel Drees

  25. 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 high temperature QCD Integrated AuAu luminocity Some data shown; 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

  26. Backup Slides Axel Drees

  27. 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

  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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