Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Jet and Heavy Flavor Probes of Hot QCD Matter Peter Jacobs, LBNL

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Calibrated in p+p and p/d+A Calculable final state medium effects Why hard probes? (= perturbative processes) Calculable interactions of energetic partons with the medium  calibrated, penetrating tomographic probes

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Outline jet quenching and radiative energy loss inclusive hadron suppression heavy quark suppression dihadron correlations: modification of jet structure outlook to the LHC (not discussed: quarkonium) Most up-to-date reference:

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors pQCD in p+p at RHIC  Good agreement with NLO pQCD  pQCD should be broadly applicable at RHIC (e.g. heavy flavor production…) Inclusive jets

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Inclusive hadron spectra in 200 GeV Au+Au p T (GeV) PHENIX PHOBOS

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Jet quenching I: hadrons are suppressed, photons are not Binary collision scaling p+p

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Jet quenching II: recoiling jets are strongly modified cos(  ) p T assoc > 0.15 GeV STAR, Phys Rev Lett 95, < p T trig < 6 GeV STAR, Phys Rev Lett 91, p T assoc > 2 GeV I & II: conclusive evidence for large partonic energy loss (“jet quenching”) in dense QCD matter trigger recoil ?

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Radiative energy loss in QCD BDMPS approximation: multiple soft collisions in a medium of static color charges  E independent of parton energy (finite kinematics  E~log(E))  E  L 2 due to interference effects (expanding medium  E~L) Medium-induced gluon radiation spectrum: Total medium-induced energy loss: Transport coefficient: Baier, Schiff and Zakharov, AnnRevNuclPartSci 50, 37 (2000)

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Extracting qhat from hadron suppression data R AA : qhat~5-15 GeV 2 /fm

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors What does measure? Equilibrated gluon gas: number density  ~T 3 energy density  ~T 4  qhat+modelling  energy density pQCD result: c~2 (  S ? quark dof? …) sQGP (multiplicities+hydro): c~10 R. Baier, Nucl Phys A715, 209c Hadronic matter QGP ~RHIC data Model uncertainties

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors BDMPS(ASW) vs. GLV Baier, Dokshitzer, Mueller, Peigne, Schiff, Armesto, Salgado, Wiedemann, Gyulassy, Levai, Vitev  Rough correspondence: (Wiedemann, HP2006)  BDMPS GLV Medium-induced radiation spectrum Salgado and Wiedemann PRD68 (2003)  x cold matter density

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Alternatively: AdS/CFT Liu, Rajagopal and Wiedemann hep-ph/ Rajagopal, HP2006

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors R AA only provides lower bound on The limitations of R AA

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Inclusive hadrons and surface bias ? Inclusive measurements  insensitive to opacity of bulk Eskola et al., hep-ph/ R AA ~ for broad range of Large energy loss  opaque core More differential observables are needed to probe deeper…

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Heavy quark energy loss In vacuum, gluon radiation suppressed at  < m Q /E Q “dead cone” effect: heavy quarks fragment hard into heavy mesons Q Dokshitzer, Khoze, Troyan, JPG 17 (1991) Dokshitzer and Kharzeev, PLB 519 (2001) 199. Dead cone also implies lower heavy quark energy loss in matter: (Dokshitzer-Kharzeev, 2001)

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Heavy quarks are “grey probes” Wicks, Horowitz, Djordjevic and Gyulassy, nucl-th/ Origin of surviving jets (radial propagation only) jets go thataway  Heirarchy of “surface bias” correlated with opacity/suppression  differential probes of the medium R AA

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Heavy flavor suppression via b,c  e+X Gluon density/qhat constrained by light quark supression+entropy density (multiplicity)  under-predicts electron suppression  charm vs beauty? elastic energy loss? …? R AA (non-photonic electrons) ~ 0.2 ~ R AA (   ) !! S.Wicks et al., nucl-th/ Armesto et al., Phys.Lett.B637: ,2006

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors b vs c suppression p T ~5 GeV/c: c  e suppression ~0.2  puzzle resolved if c  e dominates non-photonic electron spectrum - is that permissible? S.Wicks et al., nucl-th/ R AA

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors N. P. electrons in p+p vs FONLL ~factor 2 CDF, PRL 91, (2003) D0D0 FONLL M. Cacciari, Hard Probes State of the art: F ixed -O rder N ext-to- L eading L og STAR, nucl-ex/ Tevatron charm and beauty vs FONLL: OK RHIC n.p. electrons: factor 3-5 excess(!) Large ambiguity in relative contribution of c  e/b  e  need to resolve b and c explicitly

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Elastic (collisional) energy loss revisited S.Wicks et al., nucl-th/ Elastic  E comparable to Radiative  E – not negligible Elastic  E important even for light quarks  revisit energy density estimates?

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Resolution of non-photonic electron suppression puzzle needs experiment: explicit measurement of c vs b suppression theory: unified framework incorporating both elastic and radiative energy loss

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Jet structure via hadron correlations p+p  dijet Full jet reconstruction in the heavy ion environment is difficult  probe jet structure via dihadron correlations trigger Phys Rev Lett 90,

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors cos(  ) p T assoc > 0.15 GeV STAR, Phys Rev Lett 95, Established results… 4< p T trig < 6 GeV STAR, Phys Rev Lett 91, p T assoc > 2 GeV

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Dihadron correlations at higher p T Recoil jet clearly seen above background but at suppressed rate differential measurement of`  E  upper bound on qhat? trigger recoil ? p T trigger >8 GeV/c Yield per trigger STAR, nucl-ex/

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Recoiling hadrons: details   No angular broadening No modification of fragmentation Recoil rate is suppressed but jet features unmodified  see only non-interacting jets? D(z T ) Recoiling hadron distribution STAR, nucl-ex/

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors  STAR preliminary T. Renk, hep-ph/ High p T dihadrons: detailed dynamical calculation Trigger direction Different geometrical biases underly trigger and recoil distributions ~75% of recoils due to non-interacting jets All bremsstrahlung models: discrete term

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Correlations and dynamics (cont’d) T. Renk, hep-ph/ Calculation ~reproduces recoil yields with params fit to R AA additional sensitivity to dynamics of the collision? (in progress…) Suggestive calculation  need larger dynamic range in p T trig and p T assoc to probe energy loss (not only discrete term) Ultimately:  +jet (experimentally challenging, in progress) T. Renk, HP2006 Various models of bulk expansion

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Medium response to jet energy loss I PHENIX, QM05 and nucl-ex/ Leading hadrons Medium away near STAR, Phys Rev Lett 95, Look at low p T recoils… experimentally challenging to discriminate signal/bkgd new development: 3-particle correlations Mach cone, Cerenkov radiation,…?

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Medium response to jet energy loss II Au+Au 0-10% preliminary 3<p t,trigger <4 GeV p t,assoc. >2 GeV Armesto et al, nucl-ex/ Near-side “ridge” correlated with jet trigger   Induced radiation dragged by longitudinally expanding fluid?

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Jet quenching at the LHC Pb+Pb at 5.5 TeV: First ion collisions 2008 qualitatively new probes  full (~unbiased) jet reconstruction in HI events

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Summary Experiment jet quenching is well-established: multiple strong effects key open issue: how does the medium respond to  E? second generation of high precision measurements: heavy flavor, correlations,  +jet RHIC upgrades (charm reco), high luminosity (  +jet) LHC brings qualitatively new physics Theory qualitative but not yet quantitative understanding of jet quenching significant uncertainties in underlying mechanism (elastic vs radiative) heavy quark production modeling of dynamical evolution

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Final comment Current theoretical uncertainties present the largest barrier to quantitative understanding and full exploitation of RHIC and LHC Heavy Ion measurements The situation is analogous to the early days of the Solar Neutrino puzzle: We need a Standard Solar Model for Ultra-relativistic Heavy Ion physics (The good news: this is in progress)

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Extra slides

Future Prospects in QCD BNL, July 17-22, Jets and Heavy Flavors Further limitation of R AA Can R AA of light quarks/gluons constrain the energy loss distribution? T. Renk (HP2006): accurate geometry/expansion, toy models for P(  E) Can always tune medium density to reproduce R AA :  only weak constraint on e-loss distribution Prob. distributions for parton to lose  E parton with E<0.5 GeV is absorbed by medium More differential observables are needed to probe deeper…