Charm and Beauty at the LHC Andrea Dainese
Charm and Beauty at the LHC Andrea Dainese Padova – University and INFN SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 1
Contents Novel Aspects of heavy ions at the LHC Phenomenology of heavy quarks Our “eyes” to “see” heavy quarks: ALICE, CMS, (ATLAS) Selected examples of the physics potential in the open heavy-flavour sector Warning: no quarkonia here (see R. Vogt’s and S. Petrushanko’s talks) SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 2
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 LO p. QCD by I. Vitev, hep-ph/0212109 • g + jet correlations • Z 0 + jet correlations SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 3
Novelties at LHC (2): Small x C Unexplored low-x region will be probed in pp, p. A and AA collisions y= 0@ LH down to x ~10 -4 already at central y Window on the rich phenomenology of high-density PDFs shadowing / saturation effects / Color Glass recombination effects in gluon evol. even in pp coll. (more later) SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 4
Heavy-flavour production pp collisions: p. QCD factorization (see R. Vogt’s talk) p c D c p D (p. A) AA: binary scaling for hard yields “broken” by initial-state effects (shadowing, …) and final-state effects (energy loss, coalescence, …) Pb D c Pb c SQM 04 - Cape Town - September 17, 2004 medium formed in the collision Andrea Dainese u D 5
Heavy-quark phenomenology (selected topics) D Pb c medium formed in the collision u D Heavy-quark production: in p. QCD and in event generators (PYTHIA) Heavy-quark energy loss Charm coalescence and elliptic flow (see D. Molnar’s talk) Charm as a probe of low-x gluon densities (later, in pp appendix) SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 6
Heavy-quark production (pp coll. ) NLO p. QCD calculation available (e. g. MNR program*) large uncertainty (more than factor 2) due to choice of c and b masses and of scales (m. R, m. F) important to measure low pt! however, s scaling 14 Te. V (pp) 5. 5 Te. V (Pb-Pb) robust! varying D production 14 Te. V/5. 5 Te. V D production pp @ 14 Te. V * M. L. Mangano, P. Nason and G. Ridolfi, Nucl. Phys. B 373 (1992) 295. SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 7
Heavy-quarks MC simulation NLO programs are not event generators* Use PYTHIA: LO + some NLO topologies in parton shower Pair Creation (PC) Flavour Excitation (FE) Q Q Q hard scattering Q Gluon Splitting (GS) Q Q parton shower * Recently, MC @ NL 0 (Frixione-Weber) combined full NLO M. E. with HERWIG parton shower SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 8
(ALICE) Baseline for cc / bb production Cross sections from NLO p. QCD with “best guess” set of parameters Kinematics from PYTHIA tuned to reproduce NLO pt distributions system shadowing pp 14 Te. V Pb-Pb 5. 5 Te. V (5% cent) MNR 11. 2 / 0. 5 1 / 1 0. 16 / 0. 007 6. 6 / 0. 2 0. 65 / 0. 85 115 / 4. 6 PYTHIA pair creation (PC) flavour excitation (FE) gluon splitting (GS) TOTAL c-cbar: FE + GS flat Df b-bbar: ALICE baseline: N. Carrer and A. Dainese, ALICE-INT-2003 -019, hep-ph/0312255. SQM 04 - Cape Town - September 17, 2004 Andrea Dainese PC (low pt) back-to-back + FE (high pt) flat Df 9
Final-state effects in nucleus-nucleus: Parton Energy Loss Partons travel ~ 5 fm in the high colour-density medium Energy loss by gluon radiation path length L (BDMPS) hard parton Casimir coupling factor: 4/3 for quarks 3 for gluons Medium transport coefficient gluon density and momenta Probe the medium R. Baier, Yu. L. Dokshitzer, A. H. Mueller, S. Peigne' and D. Schiff, (BDMPS), Nucl. Phys. B 483 (1997) 291. SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 10
Lower E loss for heavy quarks? In vacuum, gluon radiation suppressed at q < m. Q/EQ “dead cone” effect Q 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 Yu. L. Dokshitzer and D. E. Kharzeev, Phys. Lett. B 519 (2001) 199 [hep-ph/0106202]. N. Armesto, C. A. Salgado and U. A. Wiedemann, Phys. Rev. D 69 (2004) 114003 [hep-ph/0312106]. SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 11
Estimates of RAA 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 LHC RHIC Au-Au 200 Ge. V RHIC analysis: A. D. , C. Loizides and G. Paic, hep-ph/0406201. N. Armesto, A. D. , C. A. Salgado and U. A. Wiedemann, in preparation. SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 12
Experimental study of heavy flavours in HIC at the LHC CMS ATLAS The dedicated HI experiment HI Letter of intent SQM 04 - Cape Town - September 17, 2004 Andrea Dainese Strong HI program 13
Tracking & Vertexing D mesons ct ~ 100– 300 mm, B mesons ct ~ 500 mm Secondary vertex capabilities! Impact param. resolution! acceptance: pt > 0. 2 Ge. V/c rf < 50 mm for pt > 1. 5 Ge. V/c acceptance: pt > 1 Ge. V/c rf < 50 mm for pt > 2. 5 Ge. V/c B = 0. 5 T B=4 T Dpt/pt < 2% up to 100 Ge. V/c Dpt/pt < 2% up to 10 Ge. V/c < 9% up to 100 Ge. V/c SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 14
Lepton and Hadron ID D and B: large B. R. to leptons: ~10% e + ~10% m ALICE: Ø electrons: Transition Rad. + d. E/dx in |h| < 0. 9 and pt > 1 Ge. V/c Ø muons: 2. 5< h <4 and pt >1 Ge. V/c (use pz to punch through abs. !) CMS (ATLAS): Ø muons: |h| < 2. 4 (3) and pt > 3. 5 (4) Ge. V/c Ø electrons in EM cal? (no heavy-ion studies yet) With leptons, difficult to measure D(B) pt distr. and go to low pt (loose pt correlation) Exclusive hadronic decay channels (charm) Need PID (kaons!) to reject huge combin. background in AA ALICE hadron ID: large TPC + high-res TOF + RICH (see O. Villalobos’ talk) SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 15
ALICE: Exclusive charm D 0 K-p+ Ideal tool to study RAA and low pt effects Large combinatorial background (d. Nch/dy=6000 in central Pb-Pb!) Main selection: displaced-vertex selection pair of opposite-charge tracks with large impact parameters good pointing of reconstructed D 0 momentum to the primary vertex Invariant mass analysis to “count” D 0 SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 16
D 0 Results Pb-Pb (K, ) Invariant Mass distribution (pt –integrated) in Pb-Pb (~ 1 month run) Stat. and syst. errors on D pt distr. estimated for pp and Pb-Pb Statistical significance: 1 < pt < 14 Ge. V/c N. Carrer, A. D. and R. Turrisi, J. Phys. G 29 (2003) 575. A. D. Ph. D thesis (2003), nucl-ex/0311004. SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 17
pp Sensitivity to NLO p. QCD params s = 14 Te. V SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 18
Pb-Pb pp Charm Quenching Low pt (< 6– 7 Ge. V/c) Nuclear shadowing SQM 04 - Cape Town - September 17, 2004 ‘High’ pt (6– 15 Ge. V/c) here energy loss can be studied (it’s the only expected effect) Andrea Dainese 19
Pb-Pb Open Beauty with Electrons Inclusive B e + X: electron ID + cut on its pt & on its impact parameter d 0 S/(S+B) S per 107 Pb-Pb events pt > 2 Ge. V/c, d 0 > 180 mm: 50, 000 electrons with S/(S+B) = 90 % In progress: study pt range and sensitivity to b cross section M. Lunardon and R. Turrisi SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 20
Pb-Pb Open Beauty with Muons (1) Single muon cut pt > 2 Ge. V/c Dimuon combinatorial bkgd subtracted with evt-mixing SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 21
Pb-Pb Open Beauty with Muons (2) Combined fit of low-mass, high-mass dimuons and single muons with shapes from MC to extract muons from B Use MC to exctract down to ~2 Ge. V/c! systematic error analysis in progress R. Guernane SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 22
Pb-Pb CMS: B J/y (+X) mm (+X) (more in S. Petrushanko’s talk) Displacement of m+m- vertex pt distribution of J/y from B primary J/y from B ALICE can do the same with from O. Kodolova @ “Physics at LHC 2004” e + e- I. P. Lokhtin and A. M. Snigirev, J. Phys. G 27 (2001) 236 SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 23
Pb-Pb ATLAS: b-tagged Jets (more in J. Klay’s talk) Rejection Based only on impact parameter selection Central Pb-Pb (HIJING) events Rejection factor against light-quark jets vs b-tagging eff. Factor 50 rejection when efficiency 40% required Should improve when combined with m tagging Efficiency SQM 04 - Cape Town - September 17, 2004 Andrea Dainese slide from L. Rosselet @ “Physics at LHC 2004” 24
pp Charm and low-x gluon dynamics SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 25
pp 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 For charm at pt 0: Ø x 1~x 2 ~ 10 -4 at y = 0 Ø min(x 1, x 2) ~ 10 -5 at y = 3 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. B 660 (2003) 211 [hep-ph/0211239]. K. J. Eskola, V. Kolhinen and R. Vogt, Phys. Lett. B 582 (2004) 157 [hep-ph/0310111]. SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 26
pp Charm: nonlinear/DGLAP vs pt Strongly dependent on choice of mass and scale* (Q 2) Varies from 1. 5 to 5 “Enhancement” limited to pt < 2 Ge. V/c ALICE could address it with D 0 at low pt Caveat: effect currently calculated only at LO SQM 04 - Cape Town - September 17, 2004 Andrea Dainese * m. R = m. F = Q 27
pp How to detect the enhancement due to nonlinear effects? The idea is that the effect (enh. only at very low pt) cannot be mimicked by NLO p. QCD In practice: consider ratio “Data/Theory” for all reasonable choices of theory parameters SQM 04 - Cape Town - September 17, 2004 Data: mc = 1. 3 Ge. V, Q 2 = m. T 2 and enhancement Andrea Dainese A. D. et al. , hep-ph/0403098. Data: mc = 1. 2 Ge. V, Q 2 = 4 m. T 2 and enhancement 28
Summary The LHC energy will provide new tools for the study of highdensity QCD matter; in particular heavy quarks! Heavy-quark phenomelogy is very rich from very low pt: probe small-x structure of p (and nucleus) to very high pt: probe the medium via energy loss Excellent “heavy-quark busters” (ALICE, ATLAS, CMS) are being built at CERN Heavy quarks will be one of the hottest topics of heavy-ion physics in the LHC era SQM 04 - Cape Town - September 17, 2004 Andrea Dainese 29
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