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Energy Loss in Dense Media “Jet Quenching” Axel Drees, University Stony Brook EINN, Milos Greece, Sep. 23 2005 One of the first discoveries at RHIC! PHENIX PRL 88 (2002) 22301 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 The Phase Diagram of Nuclear Matter QGP in Astrophysics RHIC Relativistic Heavy Ion Collisions 170 MeV 1Gev/fm3 early universe: time < 106 seconds possibly in the interior of neutron stars Quest of heavy ion collisions Quark-Gluon Plasma Critical point create QGP as transient state in heavy ion collisions verify existence of QGP study properties of QGP Early Universe Hadron Gas “frozen Quarks” nuclei Color superconductor Color-flavor locking mbaryon or nucleon density Neutron Stars? Overwhelming evidence for strongly interacting plasma produced at RHIC Axel Drees Matter at RHIC has 15 GeV/fm3 III. Jet Quenching I. Transverse Energy PHENIX 130 GeV V2 central 2% 1 1 dE T Bj 2 R ct0 dy PHENIX Huovinen et al Bjorken estimate: t0 ~ 0.3 fm dNg/dy ~ 1100 ~15 GeV/fm3 II. Hydrodynamics Initial conditions: ttherm ~ 0.6 -1.0 fm/c ~15-25 GeV/fm3 Pt GeV/c Axel Drees Ideal Experiment to Probe the QGP Rutherford experiment SLAC electron scattering a atom e proton discovery of nucleus 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 Jets: A Penetrating Probe for Dense Matter leading particle hadrons schematic view of jet production 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 hadrons leading particle q Jet production can be observed as high pT leading particles angular correlation In a gold gold collision q leading particle Scattered partons travel through dense matter Expected to loose a lot of their energy hadrons hadrons leading particle Energy loss observed as suppression of high pT leading particles reaction plane suppression of angular correlation Depending on path length, i.e. centrality and angle to reaction plane Axel Drees Particle Spectra from p-p Collisions Jet production measured indirectly by 0 from p-p collisions transverse momentum (pT) spectrum Identified particles (0) Charged particles (h = , K, p, .. ) yield ( pT ) 1 dN Nevt pT dpT 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 QCD calculation soft hard with QCD Data agrees with QCD calculation “calibrated” reference Axel Drees 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” Participants NN hard hard AA Nbinary hard NN TAA inel NN Axel Drees Binary Scaling in Au-Au tested with Direct Photons pp collisions: g q q g 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 yield ( AuAu )N R p ( pp) scale withyield Nbinary coll AA T Axel Drees Suppression of 0 in Central AuAu Collisions PRL 91 (2003) 72301 Nuclear modification factor: yield ( AuAu ) Ncoll RAA pT yield ( pp) PHENIX PHENIX preliminary High pT suppressed by factor ~ 5 pp to central AuAu and peripheral to central Au-Au Axel Drees Control Experiment with d-Au deuteron gold collision gold-gold collision 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 RdA 1 Initial state saturation effect Gluon density saturated in incoming gold nucleus RdA Deuteron shows no or little saturation Expect suppression of jet yield, but with reduced magnitude Final state effect: no suppression Initial state effect: suppression RAA 0.7 Axel Drees Suppression at Parton Level No suppression for direct photons Hadron suppression persists up to >20 GeV jets Common suppression for 0 and h; it is at partonic level Typical model calculation: > 15 GeV/fm3; dNg/dy > 1100 Hot opaque partonic medium: > 15 GeV/fm3 Axel Drees 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/0 constant xT scaling Convolute jet absorption or energy loss with nuclear geometry (many publications) Centrality dependence characteristic for jet absorption in extremely opaque medium! Insensitive to details of energy loss mechanism Axel Drees Azimuthal Correlations from Jets p+p Trigger particle with high pT > pT cut 1 0 Df to all other particles with pT > pT cut-2 0 /2 Df Au+Au elliptic flow random background 0 0 pp jet+jet Au+Au ??? /2 Df statistical background subtraction STAR Au-Au suppression? Jet correlations in Au-Au via statistical background subtraction 0 0 /2 AxelDf Drees Disappearance of the “Away-Side” Jet trigger 6 <pt< 8 GeV partner 2 < pt < 6 GeV Integrate yields in some f window on near and away side pedestal and flow subtracted 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 Suppression of Back-to-Back Pairs Near side Jet correlation strength: IAA = Away side yield(AuAu) background expected Compared to jet absorption model (J.Jia et al.) Away side jets are suppressed consistent with jet absorption in opaque medium “Mono jets” point outward Axel Drees Remaining Jets from Matter Surface “Mono jets” point outward Surviving “Di jets” tangential 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV D. Magestro, QM2005 STAR Preliminary ~factor 5 Qualitatively consistent with surface emission Decreased surface/volume Axel Drees Where Does the Energy Go? partner > 1 GeV Trigger > 2.5 GeV Axel Drees Modification of Jet Shape at Lower pT Near side Away side PHENIX preliminary Can jet shape be related to properties of matter? Axel Drees Theoretical Speculation: Energy loss of jet results in conical shock wave in strongly interacting plasma Hydrodynamic mach cone? Longitudinal modes ? Cherenkov radiation ? Momentum conservation Wake effect or “sonic boom” Shuryak et al. “multiple scattering” with meduium Medium evolution of radiated gluons Sound velocity? Dielectric Constant? Jet Tomography will be power tool to probe matter! Axel Drees How opaque is the medium? Check Charm Production! e,m p+p X Signal: p D p Background: 0 e g e background subtracted electron spectrum 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 pp PHENIX preliminary Axel Drees 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 Heavy Quark Energy Loss: Nuclear Modification Factor R AA d3N 3 dp AA d 3σ TAA 3 dp pp 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 Elliptic Flow: A Collective Effect f z y x dn/df ~ 1 + 2 v2(pT) cos (2 f) + ... Initial spatial anisotropy is converted into momentum anisotropy Axel Drees Charm Quarks flow with light quarks Greco,Ko,Rapp: PLB595(2004)202 Charm flows, strength ~ 60% of light quarks (0) 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 Summary & Outlook Strongly interacting QGP produced at RHIC State of unprecedented energy density ~ 15 GeV/fm3 Opaque to colored “hard” probes, jets and heavy flavor Hard probes will be critical to study properties of QGP On tape; analysis ongoing 2004 2001 4x larger Au-Au data sample in 2006 2002 Factor 10 luminosity increase with electron cooling after 2010 Discovery of jet quenching Most data seen today Axel Drees Backup Slides Axel Drees Outlook into the “Away” Future g-jet: the golden channel for jet tomography Quark gluon Compton scattering: g q q g PHENIX Preliminary pQCD direct g + jet quenching AuAu 200 GeV 0-10% g-energy fixes jet energy g & Jet direction fix kinematics measure DE as function of: E, “L”, flavor pQCD direct g 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