Heavy Ion Physics at the LHC Santa Fe

Heavy Ion Physics at the LHC Santa Fe, October 23 rd, 2005 Heavy Quarks in view of the LHC Andrea Dainese Padova – Università e INFN Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 1

Layout High-p. T (heavy-flavour) particle production in hadronic collisions –from pp to AA– in factorized QCD pp baseline: p. QCD 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? Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese PARTON ENERGY LOSS 2

Heavy-flavour production: pp proton-proton collisions: factorized p. QCD approach s /2 x 1 Q 2 x 2 PDF: • Q 2 evolution calculated in p. QCD • initial condition from data (HERA) D c c D FF: • non-perturbative • phenomenolgy + fit to the data (e+e-) calculable as perturbative series of strong coupling as(m. R) Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 3

pp QQ: p. QCD 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 p. T B production at Tevatron (1. 96 Te. V) Charm production slightly underpredicted is well described by FONLL at Tevatron (1. 96 Te. V) & at RHIC (200 Ge. V) Cacciari, Frixione, Mangano, Nason and Ridolfi, JHEP 0407 (2004) 033 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 CDF, PRL 91 (2003) 241804 FONLL: Cacciari, Nason Q e +X Cacciari, Nason, Vogt, hep-ph/0502203 Andrea Dainese 4

Heavy-flavour production: AA Binary scaling for hard yields: c A c D D medium formed in D the collision Binary scaling is “broken” by: • initial-state effects: PDF (anti)shadowing k. T broadening (‘Cronin’) • final-state effects energy loss? [next slide] in-medium hadronization (recombination? ) Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 u D fg. Pb / fgp 2 Q 2 = 5 Ge. Vrecombination: k p. Hk= S pq L T baryon/meson enhancement RAB A 1 Cronin enhancement LHC RHIC SPS p. H = z pq>1 RAA fragmentation: <1 ~1 ~2 -4 Ge. V/c Andrea Dainese p. T x 5

Calculating Parton Energy Loss BDMPS-Z formalism path length L w k. T transport coefficient Radiated-gluon energy distrib. : l (BDMPS case) Casimir coupling factor: 4/3 for q, 3 for g sets the scale of the radiated energy related to constraint k. T < 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. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 6

Model vs RHIC “light” data Model: p. QCD + E loss probability + detailed collision geometry Density ( ) “tuned” to match RAA in central Au-Au at 200 Ge. V (Quark Matter 05) Dainese, Loizides, Paic, EPJC 38 (2005) 461. matches p. T-indepence of suppression at high p. T Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 7

Lower E loss for heavy quarks ? In vacuum, gluon radiation suppressed at q < m. Q/EQ Gluonsstrahlung probability “dead cone” effect Q Dead cone implies lower energy loss (Dokshitzer-Kharzeev, 2001): energy distribution wd. I/dw of radiated gluons suppressed by angledependent factor Dokshitzer suppress high-w tail Detailed massive calculation confirms this qualitative feature R = 105 (Armesto, Salgado, Wiedemann, PRD 69 (2004) 114003) Dokshitzer, Khoze, Troyan, JPG 17 (1991) 1602. Dokshitzer and Kharzeev, PLB 519 (2001) 199. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 8

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 p. T [large uncertainties!] Basically no effect in “safe” p. T-region Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 9

c + b (? ) decay e RAA at RHIC FONLL: Electron spectrum may be ~50% charm + ~50% beauty for 3 < p. T < 8 Ge. V Due to larger mass of b quark electron RAA incresed to ~0. 4 (mass uncertainty also studied) FONLL p. QCD Cacciari, Nason, Vogt, hep-ph/0502203 Armesto, Cacciari, Dainese, Salgado, Wiedemann, in preparation, Armesto @ Quark Matter 05 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 10

Heavy-flavour data in Au-Au 200 Ge. V PHENIX (nucl-ex/0510047) STAR (preliminary, QM) Reminder: FONLL@Tevatron: D production underpredicted B, instead, is OK mass and scale uncertainty RAA down to 0. 3 for p. T > 4 Ge. V/c! Heavy-quark quenching. Similar to that of light! Small room for mass effect … Data lower than energy loss calculations, but charm fraction may be higher than predicted by FONLL Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027 + w/Cacciari, in preparation Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 11

Layout High-p. T (heavy-flavour) particle production in hadronic collisions –from pp to AA– in factorized QCD pp baseline: p. QCD 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? Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 12

Novelties at LHC (1): Hard Probes LHC: large hard cross sections! Our set of “tools” (probes) becomes richer quantitatively: qualitatively: • heavy quarks LO p. QCD by I. Vitev, hep-ph/0212109 • g + jet correlations • Z 0 + jet correlations Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 13

Heavy-quark production at the LHC pp: Important test of p. QCD 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: system : Pb-Pb (0 -5% centr. ) s. NN : 5. 5 Te. V p-Pb (min. bias) 8. 8 Te. V pp 14 Te. V 7. 2 / 0. 3 0. 8 / 0. 03 0. 84 / 0. 90 11. 2 / 0. 5 0. 16 / 0. 007 -- 4. 3 / 0. 2 115 / 4. 6 0. 65 / 0. 80 Theoretical uncertainty of a factor 2— 3 (next slide) * M. Mangano MNR code: Mangano, Nason, Ridolfi, NPB 373 (1992) 295. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 14

Theoretical Uncertainties (HERA-LHC Workshop) Evaluation of theoretical uncertainties charm beauty MNR code: Mangano, Nason, Ridolfi, NPB 373 (1992) 295. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 15

Model Comparisons (HERA-LHC Workshop) Compare predictions by several different models charm beauty Good agreement between collinear factorization based calculations: FO NLO and FONLL k. T factorization (CASCADE) higher at large p. T Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 16

Energy extrapolation via p. QCD? Different systems (pp, p-Pb, Pb-Pb) will have different s values Results in pp at 14 Te. V will have to extrapolated to 5. 5 Te. V (Pb-Pb energy) to compute, e. g. , nuclear modification factors RAA p. QCD: “there ratio of results at 14 Te. V/5. 5 Te. V has ‘small’ uncertainty” charm 12% Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 beauty 8% Andrea Dainese 17

Novelties at LHC (2): Small x Probe unexplored small-x region with HQs at low p. T and/or forward y down to x~10 -4 with charm already at y=0 increasing s Window on the rich phenomenology of high-density PDFs: gluon saturation / recombination effects Possible effect: enhancement of charm production at low p. T w. r. t. to standard DGLAP-based predictions, even in pp! Eskola, Kolhinen, Vogt, PLB 582 (2004) 157 Gotsmann, Levin, Maor, Naftali, hep-ph/0504040 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese sc(DGLAP+non-linear) sc(DGLAP) 18

Probing nuclear initial state PDFs with HQs Shadowing in p. A (AA) CGC in p. A (AA) Double parton scattering in p. A c c Eskola, Kolhinen, Salgado, EPJC 9 (1999) 61 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 19

Probing nuclear initial state PDFs with HQs Shadowing in p. A (AA) CGC in p. A (AA) Double parton scattering in p. A c c Saturation scale Qs 2(x) ~ xg(x)A/RA 2 ~ xg(x)A 1/3 At LHC for x~10 -4, Qs~1. 5 -2 Ge. V > mc For m. T, c~Qs, charm prod. CGC-dominated: • scales with Npart in p. A (not Ncoll) • harder p. T spectra, since typical k. T~Qs~1. 5 Ge. V, while in standard factorization k. T~LQCD~0. 2 Ge. V Kharzeev, Tuchin, NPA 735 (2004) 248 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 20

Probing nuclear initial state PDFs with HQs Shadowing in p. A (AA) CGC in p. A (AA) Double parton scattering in p. A c c probe “many-body” PDFs normal and anomalous: different A dep. predicted rate: cccc/cc ~ 10% (Treleani et al. ) signature: events with “tagged” DD (can use D 0+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 Cattaruzza, Del Fabbro, Treleani, PRD 70 (2004) 034022 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 21

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? Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 22

Heavy Flavour RAA at LHC Baseline: PYTHIA, with EKS 98 shadowing, tuned to reproduce c and b p. T distributions from NLO p. QCD (MNR) (m/E)-dep. E loss with * EKRT Saturation model: Eskola, Kajantie, Ruuskanen, Tuominen, NPB 570 (2000) 379. Andrea Dainese 23 Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. MNR: Mangano, Nason, Ridolfi, NPB 373 (1992) 295. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005

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 mass effect For 10 < p. T < 20 Ge. V, 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, PRD 71 (2005) 054027 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 24

Azimuthal asymmetry (v 2) The azimuthal asymmetry --v 2 or RAA(f)-- of D and B mesons in non-central collisions tests: f = p/2 f=0 PHENIX p 0 v 2 at low/moderate p. T: recombination scenario, v 2 of c/b quarks, hence degree of thermalization of medium at higher p. T: path-length dependence of E loss (almond-shaped medium => v 2 ~ 0. 05 --0. 10) heavy-flavour e go down as well? Cole @ Quark Matter 05 v 2 from E loss: Dainese, Loizides, Paic, EPJC 38 (2005) 461 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 25

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 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 26

EXTRA SLIDES Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 27

B. Muller’s QM Theory Summary RHIC data s. QGP Density of scatterings Range of color force QGP Baier’s plot Cold nuclear matter Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 1/Ntrig d. N/dj Pion gas Emergence of away-side jet will make determination of q^ easier. 8 < p. T(trig) < 15 Ge. V/c p. T(assoc) > 5 Ge. V/c Andrea Dainese STAR Preliminary 28

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 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 29

Application: Parton Quenching Model QW + Glauber-based medium geometry and density profile + PYTHIA for parton generation and fragmentation The procedure in short: 1) generate parton (q or g) with PYTHIA (or back-to-back pair) 2) calculate its L and average along the path 3) use quenching weights to get energy loss 4) quench parton and then hadronize it (independent fragm. ) p. T – D E Dainese, Loizides, Paic, EPJC 38 (2005) 461. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese Fragmentation PYTHIA p. T d. N/dp. T 30

Calculating Parton Energy Loss gluons volume-density and interaction cross section Probe the medium Finite parton energy (qualitatively) v If E < wc (e. g. small p. T parton with large L): Ø dependence on parton energy Ø : smaller sensitivity to density Ø Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 31

Model vs RHIC data Centrality dependence of RAA Centrality evolution according to Glauber-model collision geometry p. T > 4. 5 Ge. V Dainese, Loizides, Paic, EPJC 38 (2005) 461. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 32

Model vs RHIC data Disappearence of the away-side jet near side away side STAR Coll. , PRL 90 (2003) 082302. STAR Coll. , nucl-ex/0501016. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 33

Extrapolation in c. m. s. energy Intermediate RHIC energy s = 62 Ge. V Extrapolation in s: assuming (EKRT saturation model) First test: Ngluons/volume ( s)0. 6 energy extrapolation works reasonably well EKRT: Eskola, Kajantie, Ruuskanen, Tuominen, NPB 570 (2000) 379. PHENIX Coll. , JPG 31 (2005) S 473. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 34

Model prediction for LHC Extrapolation to LHC according to saturation model gives: ? !? indep. of p. T Dainese, Loizides, Paic, EPJC 38 (2005) 461. Vitev and Gyulassy, PRL 89 (2002) 252301. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 35

Why RAA is flat Surface effect Most partons from inner part are totally absorbed Prod. points in (x, y) for partons giving hadrons with p. T > 5 Ge. V: increasing s Energy loss is “saturated”: many partons radiate all their energy before getting out Loizides, Ph. D Thesis, nucl-ex/0501017 Long path lengths exploited only by high energy partons Ø effectively, Ø RAA doesn’t increase at high p. T Ø Exercise: RAA increases with p. T Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 36

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 Ø Limited sensitivity to large RAA indep. of Ø Need more differential observables: massive partons RAA vs reaction plane study of jet shapes … Eskola, Honkanen, Salgado, Wiedemann, NPA 747 (2005) 511. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 37

Open points (2): the opacity problem Can we really probe the medium? Need to relate extracted to an energy density e (Baier) 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 d. ET/dy (Bjorken estimate) Opacity problem: the interaction of the hard parton with the medium is much stronger than expected Baier, NPA 715 (2003) 209. * Eskola, Honkanen, Salgado, Wiedemann, NPA 747 (2005) 511. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 38

Charm Energy Loss at RHIC Compute RAA for c, D, e (from D) Baseline: PYTHIA, with EKS 98 shadowing, tuned to match p. T-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 p 0, h RAA (central) Thermalize charms that lose all energy d. N/dm. T exp(-m. T/T), T = 300 Me. V Use a range in to visualize limited sensitivity of RAA to itself baseline d. N/dp. T baseline Armesto, Dainese, Salgado, Wiedemann, PRD 71 (2005) 054027. EKS: Eskola, Kolhinen, Salgado, EPJC 9 (1999) 61. Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese RAA 39

The heavy-to-light ratio: What enters the game: 1) (c) quark vs gluon (Casimir factor) 2) harder charm p. T distribution: 3) harder charm fragm. 4) mass effects RHIC RD/h > 1 RD/h up RD/h down RD/h up 1) dominates > 12 -13 Ge. V 2) and 3) ~ compensate 4) dominates below 12 Ge. V Warning: significant non-pert. effects (e. g. reco) below 6 -7 Ge. V Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 40

RAA(pt) of D mesons in ALICE ‘High’ pt (10– 20 Ge. V/c) here energy loss can be studied (it’s the only expected effect) Low pt (< 8– 10 Ge. V/c) Nuclear shadowing, recombination? 1 year at nominal luminosity (107 central Pb-Pb events, 109 pp events) Pb-Pb pp Dainese, EPJC 33 (2004) 495 E loss calc: Armesto, Dainese, Salgado Wiedemann, PRD 71 (2005) 054027 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 41

RAA(ptmin) of B mesons in ALICE Low pt (< 8– 10 Ge. V/c) Nuclear shadowing, recombination? ‘High’ pt (10– 30 Ge. V/c) here energy loss can be studied IN M LI Y R A E R P (107 1 year at nominal luminosity central Pb-Pb events, 109 pp events) Pb-Pb pp E loss calc: Armesto, Dainese, Salgado Wiedemann, PRD 71 (2005) 054027 Heavy Ion Physics at the LHC, Santa Fe, 23. 10. 2005 Andrea Dainese 42