1. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 1 Andrea Dainese Padova – University and INFN Physics potential of D-meson reconstruction in ALICE International Workshop on Heavy Flavours in Heavy Ion Collisions at the LHC

2. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 2 Contents Intro: novel aspects of heavy ions at the LHC (more) abundant hard probes small(er)-x regime Phenomenology of heavy quarks (selected topics) Exclusive D 0 -meson reconstruction in pp, p-Pb and Pb-Pb collisions in ALICE Physics potential of the measurement

3. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 3 Novelties at LHC (1): Hard Probes Hard partons and their energy loss: probe the medium LHC: large hard cross sections! Our set of “tools” (probes) becomes richer quantitatively: qualitatively: heavy quarks  + jet correlations Z 0 + jet correlations LO pQCD by I. Vitev, hep-ph/0212109

4. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 4 Novelties at LHC (2): Small x Unexplored low-x region will be probed in pp, pA and AA collisions down to x ~10 -4 already at central y Window on the rich phenomenology of high-density PDFs shadowing / saturation effects / CGC (see talk by F. Gelis) recombination effects in gluon evol. even in pp coll. (more later) y = 0 @ LHC

5. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 5 Heavy-flavour production medium formed in the collision Pb c c D D u (pA) AA: binary scaling for hard yields “broken” by initial-state effects (PDF shadowing, k t broadening …) and final-state effects (energy loss, in-medium hadronization …) p p c c D D pp collisions: high-virtuality partonic scattering pQCD collinear factorization

6. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 6 Heavy-quark phenomenology (selected topics; see also F.Gelis, A.Andronic, P.B.Gossiaux) medium formed in the collision Pb c c D D u Heavy-quark cross sections at the LHC: pQCD results and the ALICE baseline Heavy-quark energy loss Charm as a probe of small-x gluon dynamics in the proton and in nuclei

7. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 7 Heavy-quark production (pp coll.) NLO pQCD calculation available (e.g. MNR program*) large uncertainty (more than factor 2) due to choice of c and b masses and of scales (  R,  F ) however, robust  s scaling 14 TeV (pp) * M.L.Mangano, P.Nason and G.Ridolfi, Nucl. Phys. B373 (1992) 295. D production 14 TeV/5.5 TeV D production pp @ 14 TeV varying 5.5 TeV (Pb-Pb) 8.8 TeV (p-Pb)

8. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 8 ALICE baseline: N.Carrer and A.Dainese, ALICE-INT-2003-019, hep-ph/0311225. 115 / 4.60.65 / 0.856.6 / 0.2 Pb-Pb 5.5 TeV (5% cent) 0.16 / 0.0071 / 111.2 / 0.5 pp 14 TeV shadowingsystem MNRPYTHIA pair creation (PC) “LO” flavour excitation (FE) “NLO” gluon splitting (GS) “NLO” TOTAL c-cbar: FE + GS  flat  b-bbar: PC (low p t )  back-to-back + FE (high p t )  flat  Cross sections from NLO pQCD with “best guess” set of parameters Kinematics from PYTHIA tuned to reproduce NLO p t distributions (ALICE) Baseline for cc / bb production

9. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 9 Nuclear Shadowing and Charm Pb nucleus ~ 10 5 partons (mainly gluons) ‘they are so close that they fuse’ Shadowing: suppression of small-x PDFs Reduces c&b yield at low p t Look at low-p t D in p-Pb! xaxa xbxb xa+xbxa+xb f g Pb (x)/f g p (x) For charm at p t  0:  x 1 ~x 2 ~ 10 -4 at y = 0  min(x 1,x 2 ) ~ 10 -5 at y =  3 a b c

10. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 10 Final-state effects in nucleus-nucleus: Parton Energy Loss Partons travel ~ 4 fm in the high colour-density medium Energy loss by gluon radiation hard parton path length L Casimir coupling factor: 4/3 for quarks 3 for gluons Medium transport coefficient  gluon density and momenta R.Baier, Yu.L.Dokshitzer, A.H.Mueller, S.Peigne' and D.Schiff, (BDMPS), Nucl. Phys. B483 (1997) 291. (BDMPS) Probe the medium

11. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 11 Lower E loss for heavy quarks? In vacuum, gluon radiation suppressed at  < m Q /E Q  “dead cone” effect Dead cone implies lower energy loss (Dokshitzer-Kharzeev, 2001) Detailed calculation confirms this qualitative feature, although effect is small and uncertainties significant (Armesto- Salgado-Wiedemann, 2003) Exploit abundant massive probes at LHC & study the effect by measuring the nuclear modification factor for D and B Q Yu.L.Dokshitzer and D.E.Kharzeev, Phys. Lett. B519 (2001) 199 [hep-ph/0106202]. N.Armesto, C.A.Salgado and U.A.Wiedemann, Phys. Rev. D69 (2004) 114003 [hep-ph/0312106].

12. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 12 RHIC Au-Au 200 GeV Estimates of R AA for D and B Ingredients: BDMPS quenching weights for heavy quarks + Glauber-based medium geometry + LHC medium density extrapolated on the basis of hadron suppression at RHIC RHIC analysis: A.D., C.Loizides and G.Paic, Eur. Phys. J. C to appear, hep-ph/0406201. N.Armesto, A.D., C.A.Salgado and U.A.Wiedemann, in preparation. LHC

13. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 13 D 0  K -  + in ALICE Exclusive channel direct measurement of the p t distribution ideal tool to study R AA Weak decay with mean proper length c  = 124  m STRATEGY: invariant-mass analysis of fully-reconstructed topologies originating from (displaced) secondary vertices Measurement of Impact Parameters Measurement of Momenta Particle identification to tag the two decay products

14. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 14 Background multiplicity in Pb-Pb What is the background to hadronic D-meson decays? combinatorial background given by pairs of uncorrelated tracks with large impact parameter in central Pb-Pb at LHC huge combinatorial background! Simulations performed using need excellent detector response and good selection strategy

15. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 15 The ALICE Detector |  | < 0.9 TPC + silicon tracker ,  e, , K, p identification 2.5 <  < 4 muons see talk by E. Vercellin

16. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 16 Impact parameter resolution < 60  m for p t > 1 GeV/c Mainly provided by the 2 layers of silicon pixels PIXEL CELL z: 425  m r  : 50  m Two layers: r = 4 cm r = 7 cm  9.8 M

17. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 17 Time-of-flight PID TOF Pb-Pb, dN ch /dy=6000 Optimization for hadronic charm decays was studied: minimize probability to tag K as 

18. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 18 D 0  K -  + : Selection of D 0 candidates increase S/B by factor ~10 3 !

19. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 19 D 0 Results (K,  ) Invariant Mass distribution (p t –integrated) in Pb-Pb (~ 1 month run) N.Carrer, A.D. and R.Turrisi, J. Phys. G29 (2003) 575. A.D. PhD thesis (2003), nucl-ex/0311004. Stat. and syst. errors on D p t distr. estimated for pp, p-Pb and Pb-Pb Statistical significance: 1 < p t < 14 GeV/c Pb-Pb

20. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 20  s = 14 TeV Sensitivity to NLO pQCD params pp

21. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 21 Charm Quenching Low p t (< 6–7 GeV/c) Nuclear shadowing ‘High’ p t (6–15 GeV/c) here energy loss can be studied (it’s the only expected effect) Pb-Pb pp

22. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 22 Study shadowing in p-Pb at 8.8 TeV? p-Pbpp R.Grosso, PhD thesis (2004)

23. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 23 Charm and low-x gluon dynamics pp

24. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 24 Charm and low-x gluon dynamics Global fits of HERA data improved by adding nonlinear corrections to standard DGLAP partonic-evolution equations Arise from gluon recombination at small x (~10 -3 ) and, at LO, imply larger gluon density (w.r.t. to DGLAP) at small x and Q 2 Charm production in pp at LHC might be enhanced w.r.t. what expected using only DGLAP terms K.J.Eskola et al., Nucl. Phys. B660 (2003) 211 [hep-ph/0211239]. K.J.Eskola, V.Kolhinen and R.Vogt, Phys. Lett. B582 (2004) 157 [hep-ph/0310111]. For charm at p t  0:  x 1 ~x 2 ~ 10 -4 at y = 0  min(x 1,x 2 ) ~ 10 -5 at y =  3 pp

25. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 25 Charm: nonlinear/DGLAP vs p t Strongly dependent on choice of mass and scale* (Q 2 ) Varies from  1.5 to  5 “Enhancement” limited to p t < 2 GeV/c ALICE could address it with D 0 at low p t Caveat: effect currently calculated only at LO *  R =  F = Q pp

26. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 26 How to detect the enhancement due to nonlinear effects? The idea is that the effect (enh. only at very low p t ) cannot be mimicked by NLO pQCD In practice: consider ratio “Data/Theory” for all reasonable choices of theory parameters A.D. et al., hep-ph/0403098. Data: m c = 1.2 GeV, Q 2 = 4m T 2 and enhancement Data: m c = 1.3 GeV, Q 2 = m T 2 and enhancement pp

27. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 27 Summary The LHC energy will provide new tools for the study of high- density QCD matter; in particular heavy quarks! Heavy-quark phenomelogy is very rich from very low p t : probe small-x structure of p and nucleus to very high p t : probe the medium via energy loss The excellent tracking, vertexing and PID capabilities of the ALICE central barrel allow to reconstruct D mesons in a wide p t range (~0–15 GeV/c) and, thus, to address this rich physics items

28. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 28 EXTRA SLIDES

29. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 29 Heavy ions at  s NN = 5.5 TeV LHC: factor 30 jump in  s NN w.r.t. RHIC hotter, bigger, longer-living hotter, bigger, longer-living ‘drops’ of QGP very large initial temperature + small baryonic content (large |y beam |) ‘Deep de-confinement’  closer to ‘ideal’ QGP  easier comp. with theory (lattice) SPS 17 GeV RHIC 200 GeV LHC 5.5 TeV initial T~ 200 MeV~ 300 MeV> 600 MeV volume~ 10 3 fm 3 ~ 10 4 fm 3 ~ 10 5 fm 3 life-time< 2 fm/c2-4 fm/c> 10 fm/c |beam rapidity|2.95.38.6

30. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 30 Heavy-quarks MC simulation NLO programs are not event generators* Use PYTHIA: LO + some NLO topologies in parton shower Q Q Q Pair Creation (PC)Flavour Excitation (FE)Gluon Splitting (GS) hard scattering Q QQ parton shower * Recently, MC @ NL0 (Frixione-Weber) combined full NLO M.E. with HERWIG parton shower

31. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 31 BDMPS model  ktkt vacuum medium

32. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 32 PQM: R AA all centralities

33. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 33 PQM: I AA

34. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 34 PQM: ch. hadrons R AA at LHC

35. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 35 PQM: surface effect

36. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 36 ALICE Barrel |  |<0.9: B = 0.4 T TOF TPC ITS with: - Si pixels - Si drifts - Si strips PIXEL CELL z: 425  m r  : 50  m Two layers: r = 4 cm r = 7 cm  9.8 M

37. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 37 D 0  K -  + : Signal and background Signal: charm cross section from NLO pQCD (MNR program), average of results given by MRS98 and CTEQ5M PDFs (with EKS98 in Pb-Pb) signal generated using PYTHIA, tuned to reproduce p t distr. given by NLO pQCD contribution from b  B  D 0 (~5%) also included Background: Pb-Pb: HIJING (dN ch /dy=6000 ! we expect ~2500 !); pp: PYTHIA; systemshadowing pp 14 TeV 11.210.160.0007 Pb-Pb 5.5 TeV (5% cent) 6.60.651150.5 MNR Program: M.L.Mangano, P.Nason and G.Ridolfi, Nucl. Phys. B373 (1992) 295.

38. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 38 D 0  K -  + : Selection of D 0 candidates increase S/B by factor ~10 3 !

39. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 39 S/B initial (M  3  ) S/evt final (M  1  ) S/B final (M  1  ) Significance S/  S+B (M  1  ) Pb-Pb 5  10 -6 1.3  10 -3 11 % 37 (for 10 7 evts, ~1 month) pp 2  10 -3 1.9  10 -5 11 % 44 (for 10 9 evts, ~1 year) D 0  K -  + : Results Note: with dN ch /dy = 3000, S/B larger by  4 and significance larger by  2 0–14 GeV/c1–14 GeV/c Pb-Pb, 5.5 TeV 10 7 events pp, 14 TeV 10 9 events

40. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 40 S/B initial (M  3  ) S/evt final (M  1  ) S/B final (M  1  ) Significance S/  S+B (M  1  ) 2  10 -3 1.9  10 -5 11 % 44 (for 10 9 evts, ~9 months at 10 30 cm -2 s -1 ) D 0  K -  + : Results 0.5 < p t < 1 GeV/c2 < p t < 2.5 GeV/c12 < p t < 14 GeV/c

41. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 41 What if multiplicity in Pb-Pb is lower? We used dN ch /dy = 6000, which is a pessimistic estimate Recent analyses of RHIC results seem to suggest as a more realistic value dN ch /dy = 3000 (or less) Charm production cross section: estimate from NLO pQCD (only primary production, no collective effects) average of theoretical uncertainties (choice of: m c,  F,  R, PDF) BKG proportional to (dN ch /dy) 2 We can scale the results to the case of dN ch /dy = 3000: S/B = 44 % SGNC = 74 (this only from scaling, obviously better with retuning of cuts)

42. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 42 Estimate of the errors Statistical error on the selected signal = 1/Significance Main systematic errors considered: correction for feed-down from beauty (B.R. B  D 0 is 65%!): error of ~8% assuming present uncertainty (~80%) on @ LHC Monte Carlo corrections: ~10% B.R. D 0  K  : 2.4% extrapolation from N(D 0 )/event to d  (D 0 )/dy:  pp: error on (~5%, will be measured by TOTEM)  Pb-Pb: error on centrality selection (~8%) + error on T AB (~10%) Pb-Pb pp

43. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 43 D 0  K -  + : d 2  (D 0 )/dp t dy and d  (D 0 )/dy d  (D 0 )/dy for |y| 1 GeV/c (65% of  (p t > 0)) statistical error = 7 % systematic error = 19 % from b = 9 % MC correction = 10% B.R. = 2.4 % from AA to NN = 13 % inner bars: statistical outer bars: systematic d  (D 0 )/dy for |y| 0 statistical error = 3 % systematic error = 14 % from b = 8 % MC correction = 10% B.R. = 2.4 %  inel = 5 %

44. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 44 Interpolation pp 14  5.5 TeV In pQCD calculations the ratio of the differential cross sections at 14 and 5.5 TeV is independent of the input parameters within 10% up to 20 GeV/c pQCD can be safely used to extrapolate pp @ 14 TeV to 5.5 TeV Necessary to compare Pb-Pb and pp by R AA

45. DIMUONnet - Clermont-Ferrand - December 13, 2004 Andrea Dainese 45 Gluons: DGLAP nonlinear x = 10 -3 Q = 2 m c = 2.4 GeV nonlinear (quadratic) correction has “–” sign Q 2 evolution is slower low Q 2 and x has to be larger than in DGLAP