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Heavy-quark energy loss at RHIC and LHC

Heavy-quark energy loss at RHIC and LHC. Andrea Dainese Padova – Universit y and INFN based on work in collaboration with: N.Armesto, M.Cacciari, C.Salgado, U.Wiedemann. Layout. Energy loss for massive partons à la BDMPS Model: quenching weights + geometry Results for RHIC

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Heavy-quark energy loss at RHIC and LHC

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  1. Heavy-quark energy loss at RHIC and LHC Andrea Dainese Padova – University and INFN based on work in collaboration with: N.Armesto, M.Cacciari, C.Salgado, U.Wiedemann PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  2. Layout • Energy loss for massive partons à la BDMPS • Model: quenching weights + geometry • Results for RHIC • the baseline for “non-photonic” electrons • RAA vs experimental data • Testing E loss with heavy-to-light ratios at LHC • Conclusions PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  3. path length L w kT l Parton E Loss in the BDMPS 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. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  4. Gluonsstrahlung probability Dokshitzer Q Detailed massive calculation confirms this qualitative feature R = 105 (Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003) 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. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  5. (Quark Matter 05) matches pT-indepence of suppression at high pT Model vs RHIC “light” data • Model: pQCD + E loss probability (quenching weights) + Glauber collision geometry • Density ( ) “tuned” to match RAA in central Au-Au at 200 GeV Similar results by Eskola, Honkanen, Salgado, Wiedemann Dainese, Loizides, Paic, EPJC 38 (2005) 461. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  6. Model for heavy quarks • Initially only charm • Baseline at RHIC: PYTHIA, with EKS98 shadowing, tuned to match pT-shape of D cross section measured in d-Au by STAR (QM04) • Heavy-quark E loss using (m/E)-dependent QW • extracted from p0,hRAA (central) • Thermalize charms that lose all energy dN/dmTmT exp(-mT/T), T = 300 MeV baseline dN/dpT baseline RAA Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. EKS98: Eskola, Kolhinen, Salgado, EPJC 9 (1999) 61. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  7. other contributions become important larger uncertainties Charm RAA at RHIC (extracted from light-hadron data) 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. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  8. PHENIX preliminary data (QM) vs FONLL uncertainty band Large uncertainty on b/c crossing point in pT: from scales/masses variation it changes from 3 to 9 GeV Note: still, electron cross section in pp at 200 GeV underestimated at high pT Charm + beauty + DY electrons at RHIC(pQCD baseline revised, and its uncertainties) FONLL (see Ramona’s talk): electron spectrum may be ~50% c + ~50% b for 3 < pT < 8 GeV We investigated the DY component: < 10% up to 10 GeV FONLL calculation: Cacciari, Nason, Vogt, hep-ph/0502203 Drell-Yan from: Gavin et al., hep-ph/9502372 Comparison: Armesto, Cacciari, Dainese, Salgado, Wiedemann, in preparation PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  9. PHENIX (nucl-ex/0510047) STAR (preliminary, QM) mass and scale uncertainty RAA of c and b electrons at RHIC • Due to larger mass of b quark electron RAA increased to ~0.4 • Mass uncertainty (in E loss) and scales uncertainty (in pQCD  b/c crossing) being studied mass uncertainty Armesto, Cacciari, Dainese, Salgado, Wiedemann, in preparation Armesto @ Quark Matter 05 PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  10. f = p/2 f = 0 what about heavy-flavour e? using FONLL baseline only from E loss v2 at high pT from E loss • The azimuthal asymmetry --v2 or RAA(f)-- of D and B mesons in non-central collisions tests: • at low/moderate pT: recombination scenario, v2 of c/b quarks, hence degree of thermalization of medium • at higher pT: path-length dependence of E loss (almond-shaped medium => v2~ 0.05--0.10) PHENIX p0 v2 Cole @ Quark Matter 05 v2 from E loss: Dainese, Loizides, Paic, EPJC 38 (2005) 461 PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  11. Heavy Quark Energy Loss at LHC • ~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 What can we learn from a comparative quenching study of massive and massless probes at the LHC? PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  12. Heavy Flavour RAA at LHC • Baseline: PYTHIA, with EKS98 shadowing, tuned to reproduce c and b pT distributions from NLO pQCD (MNR) • (m/E)-dep. E loss with • * EKRT Saturation model: Eskola, Kajantie, Ruuskanen, Tuominen, NPB 570 (2000) 379. Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. MNR: Mangano, Nason, Ridolfi, NPB 373 (1992) 295. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  13. mass effect 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 RB/h enhancement probes mass dep. of E loss Color-charge and mass dep. of E loss with Heavy-to-Light ratios at LHC Heavy-to-light ratios: Compare g  h , c  D and b  B Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027 PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  14. Conclusions The (open) heavy-flavour era of heavy-ion physics has begun • Heavy flavours: testing ground for our understanding of radiative energy loss • However, we need a solid perturbative baseline: • c/b relative contribution has large th. uncertainty (e.g. FONLL)… • which, still, doesn’t accomodate RHIC pp data • DY should be included in electron comparisons at ~10 GeV • Current e data tend to be overpredicted at high pT Proposed observables at the LHC: • Heavy-to-light ratios as probes of E loss… • … color-charge dependence (RD/h) • … parton-mass dependence (RB/h) PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  15. EXTRA SLIDES PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  16. RHIC data sQGP QGP 8 < pT(trig) < 15 GeV/c STAR Preliminary pT(assoc) > 5 GeV/c 1/Ntrig dN/dj Pion gas Cold nuclear matter B.Muller’s QM Theory Summary Density of scatterings Range of color force Baier’s plot Emergence of away-side jet will make determination of q^ easier. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  17. 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 PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  18. 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. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  19. 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. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  20. ?!? 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. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  21. 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 PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  22. m/E = 0.1 massive massless dead cone R = 105 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 *Warning: large uncertainties Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  23. 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 PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  24. B production at Tevatron (1.96 TeV) is well described by FONLL Charm production slightly underpredicted at Tevatron (1.96 TeV) CDF, PRL91 (2003) 241804 FONLL: Cacciari, Nason & at RHIC (200 GeV) Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP0407 (2004) 033 Cacciari, Nason, Vogt, hep-ph/0502203 Q  e+X pp  QQ: pQCD calculations vs data • Calculation of partonic cross section • standard: Fixed Order (NLO) Massive (e.g. MNR code) • state-of-the-art: Fixed Order Next-to-Leading Log (FONLL)  more accurate at high pT PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  25. 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 PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

  26. Heavy-quark production at the LHC • pp: Important test of pQCD in a new energy domain • Remember the “15-years saga of b production at Tevatron”* • Baseline predictions: NLO (MNR code) in pp + binary scaling (shadowing included for PDFs in the Pb) • ALICE baseline for charm / beauty: Theoretical uncertainty of a factor 2—3 (next slide) * M.Mangano MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295. PANIC 2005, Santa Fe, 24.10.2005 Andrea Dainese

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