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Heavy-flavour Physics in Heavy-ion Collisions at LHC

Learn about heavy-flavour particle production in hadronic collisions, nuclear effects, Tevatron and RHIC findings, and what to expect at the LHC. Explore topics like parton energy loss and different mechanisms impacting heavy-flavour production.

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Heavy-flavour Physics in Heavy-ion Collisions at LHC

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  1. Heavy-flavour Physics in heavy-ion collisions in view of the LHC Andrea Dainese Padova – Università e INFN Padova, September 29th, 2005 Andrea Dainese

  2. PARTON ENERGY LOSS Layout • High-pT (heavy-flavour) particle production in hadronic collisions –from pp to AA– in factorized QCD • pp baseline: pQCD calculations • nuclear effects, in initial and final state • What have we learnt at Tevatron and RHIC? • What will be new at the LHC? • What do we expect? What should we measure? Disclaimer: experimentalist’s view; no quarkonia. Padova, September 29th, 2005 Andrea Dainese

  3. D s /2 x1 Q2 c x2 s /2 c D • FF: • non-perturbative • phenomenolgy • + fit to the data (e+e-) • PDF: • Q2 evolution calculated in pQCD • initial condition from data (HERA) calculable as perturbative series of strong coupling as(mR) Heavy-flavour production: pp proton-proton collisions: factorized pQCD approach Padova, September 29th, 2005 Andrea Dainese

  4. 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 Padova, September 29th, 2005 Andrea Dainese

  5. D c c D c kLkT D A Cronin enhancement RAB medium formed in the collision A u D 1 c pT ~2-4 GeV/c fgPb / fgp recombination: pH = S pq Q2 = 5 GeV2  baryon/meson enhancement LHCRHICSPS RAA<1~1>1 fragmentation: pH = z pq x Heavy-flavour production: AA Binary scaling for hard yields: A A • Binary scaling is “broken” by: • initial-state effects: • PDF (anti)shadowing • kT broadening (Cronin) • final-state effects: • energy loss? [next slides] • in-medium hadronization • (recombination?) Padova, September 29th, 2005 Andrea Dainese

  6. c 0 0.1 fm/c ~5 fm/c time D medium A IN vs. OUT probe IN (known from pp, pA + pQCD) probe OUT medium formed in the collision A u D c Hard partons as probes of the medium • Before coming to E loss… Why we love it so much: • Why hard partons and heavy quarks are probes: • large virtuality Q2 ~ Mcc2 > (2 mc)2 • happen at t = 0 “in-medium • small “formation time” Dt ~ 1/Q propagation” (for charm: Dt < 1/2mc ~ 0.1 fm/c << tQGP ~ 5–10 fm/c) • calculable in pQCD – “calibrated probes” • strong interacting – they can be “medium-modified” Q2 Padova, September 29th, 2005 Andrea Dainese

  7. path length L hard parton path length L hard parton Parton QCD Energy Loss • Partons travel ~4 fm in the high color-density medium • Bjorken (`82): energy loss due to elastic scattering • 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 Bjorken, FERMILAB-Pub-82/59-THY (1982). Gyulassy, Wang, Baier, Dokshitzer, Mueller, Peigne’, Schiff, Levai, Vitev, Zhakarov, Salgado, Wiedemann, … Padova, September 29th, 2005 Andrea Dainese

  8. path length L w kT l Calculating Parton Energy Loss 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. Padova, September 29th, 2005 Andrea Dainese

  9. 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 Padova, September 29th, 2005 Andrea Dainese

  10. (Quark Matter 05) matches pT-indepence of suppression at high pT matches centrality dependence Model vs RHIC “light” data • Model: pQCD + E loss probability + detailed collision geometry • Density ( ) “tuned” to match RAA in central Au-Au at 200 GeV Dainese, Loizides, Paic, EPJC 38 (2005) 461. Note: • No initial-state effects nor “reco”: results given for pT > 5 GeV • Band represents theoretical uncertainty  uncertainty in Padova, September 29th, 2005 Andrea Dainese

  11. 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. Padova, September 29th, 2005 Andrea Dainese

  12. 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. Padova, September 29th, 2005 Andrea Dainese

  13. Due to larger mass of b quark electron RAA incresed by 2 (mass uncertainty also studied) FONLL pQCD Cacciari, Nason, Vogt, hep-ph/0502203 Armesto, Cacciari, Dainese, Salgado, Wiedemann, in preparation, Armesto @ Quark Matter 05 c + b (?) decay e RAA at RHIC FONLL: Electron spectrum may be ~50% charm + ~50% beauty for 3 < pT < 8 GeV Padova, September 29th, 2005 Andrea Dainese

  14. Reminder: FONLL@Tevatron: D production underpredicted B, instead, is OK c only c + b (FONLL predict.) Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027 + w/Cacciari, in preparation Heavy-flavour data in Au-Au 200 GeV RAA down to 0.3 for pT > 4 GeV/c! Heavy-quark quenching. Similar to that of light! Small room for mass effect … Comparison to predictions: compatible, provided the charm fraction is higher than predicted by FONLL Padova, September 29th, 2005 Andrea Dainese

  15. Layout • High-pT (heavy-flavour) particle production in hadronic collisions –from pp to AA– in factorized QCD • pp baseline: pQCD calculations • nuclear effects, in initial and final state • What have we learnt at Tevatron and RHIC? • What will be new at the LHC? • What do we expect? What should we measure? Padova, September 29th, 2005 Andrea Dainese

  16. Novelties at LHC (1): Hard Probes • LHC: large hard cross sections! • Our set of “tools” (probes) becomes richer quantitatively: • qualitatively: • heavy quarks • g + jet correlations • Z0 + jet correlations LO pQCD by I. Vitev, hep-ph/0212109 Padova, September 29th, 2005 Andrea Dainese

  17. Heavy-quark production at the LHC • Important test of pQCD in a new energy domain • NLO (MNR code) at LHC (ALICE baseline for charm / beauty) Evaluation of theoretical uncertainties HERA-LHC Workshop Proceedings using: Mangano, Nason, Ridolfi, NPB373 (1992) 295 Theoretical uncertainty of a factor 2--3 charm beauty MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295. Padova, September 29th, 2005 Andrea Dainese

  18. Energy extrapolation via pQCD? • Different systems (pp, p-Pb, Pb-Pb) will have different s values at the LHC • Results in pp at 14 TeV will have to extrapolated to 5.5 TeV (Pb-Pb) to compute, e.g., nuclear modification factors RAA • pQCD: “there ratio of results at 14 TeV/5.5 TeV has ‘small’ uncertainty” beauty charm 12% 8% Padova, September 29th, 2005 Andrea Dainese

  19. increasing s sc(DGLAP+non-linear) sc(DGLAP) Novelties at LHC (2): Small x • Probe unexplored small-x region with HQs at low pT and/or forward y • down to x~10-4 with charm already at y=0 • Window on the rich phenomenology of high-density PDFs: gluon saturation / recombination effects • Possible effect: enhancement of charm production at low pT w.r.t. to standard DGLAP-based predictions, even in pp! Eskola, Kolhinen, Vogt, PLB582 (2004) 157 Gotsmann, Levin, Maor, Naftali, hep-ph/0504040 Padova, September 29th, 2005 Andrea Dainese

  20. c c Probing nuclear initial state PDFs with HQs • Shadowing in pA (AA) • CGC in pA (AA) • Double parton scattering in pA Eskola, Kolhinen, Salgado, EPJC 9 (1999) 61 Padova, September 29th, 2005 Andrea Dainese

  21. c c Probing nuclear initial state PDFs with HQs • Shadowing in pA (AA) • CGC in pA (AA) • Double parton scattering in pA • Saturation scale Qs2(x) ~ xg(x)A/RA2 ~ xg(x)A1/3 • At LHC for x~10-4, Qs~1.5-2 GeV > mc • For mT,c~Qs, charm prod. CGC-dominated: • scales with Npart in pA (not Ncoll) • harder pT spectra, since typical kT~Qs~1.5 GeV, while • in standard factorization kT~LQCD~0.2 GeV Kharzeev, Tuchin, NPA 735 (2004) 248 Padova, September 29th, 2005 Andrea Dainese

  22. c c predicted rate: cccc/cc ~ 10% (Treleani et al.) signature: events with “tagged” DD (can use D0+e+ or e+e+) and ch. conj. NB: there is a “background” from normal bb events, but is can be estimated from measured single inclusive b cross section Probing nuclear initial state PDFs with HQs • Shadowing in pA (AA) • CGC in pA (AA) • Double parton scattering in pA probe “many-body” PDFs normal and anomalous: different A dep. Cattaruzza, Del Fabbro, Treleani, PRD 70 (2004) 034022 Padova, September 29th, 2005 Andrea Dainese

  23. 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 (see Marcello’s talk) What can we learn from a comparative quenching study of massive and massless probes at the LHC? Padova, September 29th, 2005 Andrea Dainese

  24. Heavy Flavor 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. Padova, September 29th, 2005 Andrea Dainese

  25. mass effect 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 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 Armesto, Dainese, Salgado, Wiedemann, PRD71 (2005) 054027 Padova, September 29th, 2005 Andrea Dainese

  26. f = p/2 Theory:Greco, Ko, Rapp: PLB 595 (2004) 202 f = 0 heavy-flavour e go down as well Azimuthal asymmetry (v2) • 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(see Vincenzo’s talk) • at higher pT: path-length dependence of E loss (almond-shaped medium => v2(pT>8 GeV)~ 5-10%) PHENIX p0 v2 Cole @ Quark Matter 05 v2 from E loss: Dainese, Loizides, Paic, EPJC 38 (2005) 461 Padova, September 29th, 2005 Andrea Dainese

  27. Conclusions • The (open) heavy-flavour era of heavy-ion physics has begun • Observation of heavy-quarks quenching at RHIC ! • The LHC will be a `hard probes and heavy quarks machine’ and quenching studies will play a central role Promising observables at the LHC: • RAA of D and B mesons • Heavy-to-light ratios as probes of E loss… • … color-charge dependence (RD/h) • … parton-mass dependence (RB/h) • Azimuthal anysotropy for D, B mesons (or their decay leptons): interplay between reco/flow and E loss + study of dense QCD initial-state phenomenology Padova, September 29th, 2005 Andrea Dainese

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