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Suppression of light- n’ heavy-flavored hadrons from RHIC to LHC

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  1. CERN Heavy Ion Forum Suppression of light- n’ heavy-flavored hadrons from RHIC to LHC Andrea Dainese Padova – University and INFN based on work in collaboration with: N.Armesto, C.Loizides, G.Paic, C.Salgado, U.Wiedemann CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  2. Layout • The discovery of “jet quenching” at RHIC • High-pT particle production in nucleus-nucleus collisions, according to perturbative QCD PARTON ENERGY LOSS • Calculating parton energy loss (BDMPS-Z framework) • Light-flv hadron suppression in the Parton Quenching Model • versus RHIC data • predictions for LHC • Energy loss for heavy quarks CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  3. PHENIX p0 (0-10%) Discovery at RHIC:high-pT suppression • Nuclear modification factor of pT distributions: factor 5 suppression! compilation by D.d’Enterria CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  4. What about jets? pp  2 back-to-back jets Jets via di-hadron correlations: • trigger: highest-pT track, (4--6 GeV) • Df distribution: 2 GeV < pT < pTtrigger near side away side STAR Coll., PRL 90 (2003) 082302. slide courtesy of P.Jacobs CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  5. Discovery at RHIC:no away-side jet in central Au-Au • Quantified via ratio of integrals: ~1 in peripheral AA ~0 in central AA STAR Coll., PRL 90 (2003) 082302. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  6. Final-state effect Is it final-state energy loss? • … or saturation of the parton densities in the initial nuclei? Control experiment, without medium: d-Au no high-pT suppression the away-side jet is there PHENIX Coll., PRL 91 (2003) 072303. STAR Coll., PRL 91 (2003) 072304. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  7. h RAB Au 1 medium formed in the collision q q Au q h q ~2-4 GeV/c pT kLkT fgPb / fgp Q2 = 5 GeV2 Cronin enhancement h p pp  h+X LHCRHICSPS RAA<1~1>1 q p h x High-pt particle prod. in AA collisions • A schematic view: • Ingredients: • pp baseline (pQCD) • initial-state effects: • PDF (anti)shadowing • kT broadening (Cronin) • final-state effects: • energy loss • in-medium hadronization (coalescence) CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  8. Parton Energy Loss • Partons travel ~4 fm in the high density medium • Bjorken (`82): energy loss due to elastic scattering Bjorken, FERMILAB-Pub-82/59-THY (1982). CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  9. path length L hard parton path length L hard parton Parton QCD Energy Loss • Partons travel ~4 fm in the high color-density medium • Successive calculations (`92 ): a QCD mechanism dominates, medium-inducedgluon radiation • Coherent wave-function gluon acummulates kT due to multiple inelastic scatterings in the medium  it decoheres and is radiated kT Gyulassy, Pluemer, Wang, Baier, Dokshitzer, Mueller, Peigne’, Schiff, Levai, Vitev, Zhakarov, Salgado, Wiedemann, … CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  10. path length L w kT l Calculating Parton Energy Loss STATIC MEDIUM BDMPS-Z formalism transport coefficient Radiated-gluon energy distrib.: (BDMPS case) Casimir coupling factor: 4/3 for q, 3 for g sets the scale of the radiated energy related to constraint kT <w, controls shape at w << wc Baier, Dokshitzer, Mueller, Peigne‘, Schiff, NPB 483 (1997) 291. Zakharov, JTEPL 63 (1996) 952. Salgado, Wiedemann, PRD 68(2003) 014008. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  11. Finite parton energy (qualitatively) • If E < wc (e.g. small pT parton with large L): • dependence on parton energy • : smaller sensitivity to density Calculating Parton Energy Loss gluons volume-density and interaction cross section Probe the medium CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  12. Medium Expansion • The density of scattering centers is time-dependent: a = 1.5, 1.0, 0.5, 0 • Dynamical scaling law: same spectrum obtained for equivalent static trasport coefficient • Calculations for a static medium apply to expanding systems Salgado and Wiedemann, PRL 89 (2002) 092303 CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  13. Quenching Weights • Goal: compute high-pT suppression in BDMPS-Z framework • QW = energy loss probability distributions • Calculated from wdI/dw , in E  approximation + uncertainties BDMS, JHEP 0109 (2001) 033. Salgado and Wiedemann, PRD 68 (2003) 014008. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  14. pT dN/dpT PYTHIA Fragmentation pT – DE pT Application: Parton Quenching Model • QW + Glauber-based medium geometry and density profile + PYTHIA for parton generation and fragmentation • The procedure in short: • generate parton (q or g) with PYTHIA (or back-to-back pair) • calculate its L and average along the path • use quenching weights to get energy loss • quench parton and then hadronize it (independent fragm.) Dainese, Loizides, Paic, EPJC 38 (2005) 461. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  15. Eskola, Honkanen, Salgado, Wiedemann, NPA 747 (2005) 511 matches pT-indepence of suppression at high pT Model vs RHIC data • Density ( ) “tuned” to match RAA in central Au-Au at 200 GeV Note: • No initial-state effects nor “reco”: results given for pT > 5 GeV • Band represents theoretical uncertainty CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  16. pT > 4.5 GeV Model vs RHIC dataCentrality dependence of RAA • Centrality evolution according to Glauber-model collision geometry Dainese, Loizides, Paic, EPJC 38 (2005) 461. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  17. Model vs RHIC dataDisappearence of the away-side jet near side away side STAR Coll., PRL 90 (2003) 082302. STAR Coll., nucl-ex/0501016. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  18. Extrapolation in c.m.s. energyIntermediate RHIC energy s = 62 GeV • Extrapolation in s: assuming  Ngluons/volume  (s)0.6 (EKRT saturation model) • First test: energy extrapolation works reasonably well EKRT: Eskola, Kajantie, Ruuskanen, Tuominen, NPB 570 (2000) 379. PHENIX Coll., JPG 31 (2005) S473. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  19. ?!? Model prediction for LHC • Extrapolation to LHC according to saturation model gives: indep. of pT Dainese, Loizides, Paic, EPJC 38 (2005) 461. Vitev and Gyulassy, PRL 89 (2002) 252301. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  20. Loizides, PhD Thesis, nucl-ex/0501017 Why RAA is flat  Surface effect • Most partons from inner part are totally absorbed • Energy loss is “saturated”: many partons radiate all their energy before getting out • Long path lengths exploited only by high energy partons • effectively, • RAA doesn’t increase at high pT • Exercise: RAA increases with pT Prod. points in (x,y) for partons giving hadrons with pT > 5 GeV: increasing s CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  21. ? Open points (1): limited sensitivity of RAA • Strong suppression requires very large density • Surface emission scenario • RAA determined by geometry rather than by density itself • Limited sensitivity to • Need more differential observables: • massive partons • RAA vs reaction plane • study of jet shapes • … large  RAA indep. of Eskola, Honkanen, Salgado, Wiedemann, NPA 747 (2005) 511. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  22. PQM PQM PHENIX p0 prel. vs PQM f = p/2 f = 0 STAR Coll., PRL 93 (2004) 252301 First RAA vs f appearing … (see talk by d’Enterria)  Further handle on L-dependence* • Data show stronger f dep. than PQM model • Note: model is not DE L2, rather DEL • * Beware: effect of collective flow on RAA vs f !?! CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  23. Open points (2): the opacity problem • Can we really probe the medium? • Need to relate extracted to an energy density e • QCD estimate for ideal QGP: • A recent analysis* of RHIC data, similar to that presented, extracts energy density 5 larger than that estimated from produced transverse energy dET/dy (Bjorken estimate) • Opacity problem: the interaction of the hard parton with the medium is much stronger than expected (Baier) Baier, NPA 715 (2003) 209. * Eskola, Honkanen, Salgado, Wiedemann, NPA 747 (2005) 511. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  24. Heavy Quarks CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  25. Dokshitzer Q Lower E loss for heavy quarks ? • In vacuum, gluon radiation suppressed at q < mQ/EQ  “dead cone” effect • Dead cone implies lower energy loss(Dokshitzer-Kharzeev, 2001): • energy distribution wdI/dw of radiated gluons suppressed by angle-dependent factor • suppress high-w tail Dokshitzer, Khoze, Troyan, JPG 17 (1991) 1602. Dokshitzer and Kharzeev, PLB 519 (2001) 199. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  26. m/E = 0.1 massive massless dead cone Lower E loss for heavy quarks ? • Detailed massive calculation shows that: Medium-induced gluon radiation fills the dead cone Still, kT-integrated radiation is suppressed, but only for quite large m/E (i.e. large m, low pT)* kT R = 105 *Warning: large uncertainties Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  27. Charm Energy Loss at RHIC • Compute RAA for c, D, e (from D) • Baseline: PYTHIA, with EKS98 shadowing, tuned to match pT-shape of D cross section measured in d-Au by STAR • c-quark E loss as for light-flv hadrons, but using (mc/Ec)-dependent QW • extracted from p0,hRAA (central) • Thermalize charms that lose all energy dN/dmTmT exp(-mT/T), T = 300 MeV • Use a range in to visualize limited sensitivity of RAA to itself baseline dN/dpT baseline RAA Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. EKS: Eskola, Kolhinen, Salgado, EPJC 9 (1999) 61. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  28. Charm RAA at RHIC effect of the mass thermalized component Small effect of mass for charm (~50% for D, ~30% for e) at low pT [large uncertainties!] Basically no effect in “safe” pT-region Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  29. RAA pT (GeV) Charm Electron RAA from PHENIX RAA down to 0.3 at pT ~ 4 GeV, where effect of c mass predicted ~20-30% Reasonable agreement of prediction with data, however … CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  30. For pT < 3 GeV, computed RAA depends on T used for thermalized charm FONLL pQCD Cacciari, Nason, Vogt, hep-ph/0502203 PHENIX Charm+Beauty e RAA from PHENIX PHENIX e spectrum may be ~50% charm + ~50% beauty for 3 < pT < 8 GeV CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  31. The heavy-to-light ratio: What enters the game: • (c) quark vs gluon (Casimir factor) RD/h > 1 • harder charm pT distribution: RD/h up • harder charm fragm. RD/h down • mass effects RD/h up 1) dominates > 12-13 GeV 2) and 3) ~ compensate 4) dominates below 12 GeV Warning: significant non-pert. effects (e.g. reco) below 6-7 GeV RHIC CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  32. Heavy Quark Energy Loss at LHC • Charm (beauty) production expected to increase from RHIC to LHC by factor 10 (100) • ~100 cc pairs and ~5 bb pairs per central Pb-Pb collision • Experiments will measure with good precision RAA for D and B, and for their decay leptons (see talk by R.Turrisi) What can we learn from a comparative quenching study of massive and massless probes at the LHC? CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  33. Heavy Flavor RAA at LHC • Baseline: PYTHIA, with EKS98 shadowing, tuned to reproduce c and b pT distributions from NLO pQCD (MNR) • E loss with (m/E)-dep. QW and Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. MNR: Mangano, Nason, Ridolfi, NPB 373 (1992) 295. CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  34. Heavy-to-light ratios at LHC: charm (Small) mass effect limited to pT < 8-10 GeV, where shadowing and “reco” may be significant For 10 < pT < 20 GeV, charm behaves like a m=0 quark, light-flv hadrons come mainly from gluons RD/h enhancement probes color-charge dep. of E loss CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  35. Heavy-to-light ratios at LHC: beauty mass effect For 10 < pT < 20 GeV, dominant effect due to b mass RB/h enhancement probes mass dep. of E loss CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  36. Summary • One of the most exciting discoveries at RHIC ! • We are dealing with energy loss in an extremely opaque medium, but … • theoretically, we are just starting to learn how to probe the medium; still large uncertainties • experimentally, already going to more differential observables • vs azimuthal angle i.e. path-length -- (not understood, flow?) • vs parton species and quark mass -- c (b) SUPPRESSED! • The LHC will be a `hard probes machine’ and quenching studies will play a central role • Example: Heavy-to-light ratios as probes of E loss… • … color-charge dependence (RD/h) • … parton-mass dependence (RB/h) CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  37. EXTRA SLIDES CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  38. Comparison to massive GLV Djordjevic, Gyulassy, Wicks,hep-ph/0410372 CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese

  39. RAAD at LHC, step by step CERN Heavy Ion Forum, April 13th, 2005 Andrea Dainese