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Charm and Beauty Production: from pp and p-A to Pb-Pb, from SPS to LHC

Charm and Beauty Production: from pp and p-A to Pb-Pb, from SPS to LHC. Introduction, parton distribution functions, nuclear effects Critical review of open charm and beauty data Comparison with Pythia calculations: Charm production cross sections Charged over neutral D meson ratio

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Charm and Beauty Production: from pp and p-A to Pb-Pb, from SPS to LHC

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  1. Charm and Beauty Production: from pp and p-A to Pb-Pb, from SPS to LHC • Introduction, parton distribution functions, nuclear effects • Critical review of open charm and beauty data • Comparison with Pythia calculations: • Charm production cross sections • Charged over neutral D meson ratio • Kinematical distributions and D meson pair correlations • Beauty production cross sections • Charm from dimuons in NA60 • Measuring heavy flavours at the LHC For many more details, see: C. Lourenço & H. K. Wöhri, Phys. Rep. 433 (2006) 127. Hermine K. Wöhri, INFN Cagliari / Italy (in coll. with Carlos Lourenço) Early Time Dynamics in Heavy Ion Collisions, Montréal, Canada, 16–19 July 2007

  2. Motivation for Studying Heavy Flavours • Open charm and open beauty production provide the best reference to study quarkonia suppression (same gluons in the initial state) • B mesons are an indirect source of J/y mesons → this feed-down source must be carefully evaluated to understand the suppression of prompt J/y production • Important to measure gluon (anti-)shadowing effects in p-A collisions • Charm and beauty particles are suitable probes of gluon saturation at low x • Important to verify if there is a flavour and mass dependent parton energy loss: • DEloss(g) > DEloss(q) > DEloss(Q) • (color factor) (mass effect) • Abundant production of charm at high energies: thermalisation in the produced medium?

  3. Heavy Flavour Hadro-Production In LO pQCD the charm and beauty production cross section is given by the sum of gluon fusion and quark-antiquark annihilation gg ij = qq Parton distribution functions(prob. of finding a parton in a hadron, with a given fractional momentum, x) gluon fusion dominates the cross section charm gg / total similar for beauty

  4. x fp(x,Q2) x fp(x,Q2) x x Parton Distribution Functions Several groups (MRST, CTEQ, GRV, etc.) extracted PDF parametrisations from (DIS, etc) data x-rangesfor charmproductionat differentenergies(at y ~ 0) Pion parametrizationsare much older

  5. anti-shadowing shadowing Nuclear Effects on the PDFs The probabilities of finding partons of given xare different if the proton is inside a nucleus. The EKS98 model allows us to calculate thenuclear modification factor : Shadowing factors for Pb-Pb (total c.s.) Note:shadowingdepends ony, pT and b

  6. Measurements of D meson Production Cross Sections Energy range : Elab = 200–920 GeV (fixed target) ; s = 1.96 TeV (CDF) Linear nuclear dependence assumed :(anti-shadowing effects can be neglected, < 10%) D0→ K-p+ D+→ K-p+p+ ~

  7. D+→ K-p+p+ time measured D0→ K-p+ published Corrections Applied to the Published Values • To achieve the best possible compilation, the measurementswere carefully selected and some corrections were applied • Only hadro-production experiments; oldest ones excluded • Use the latest branching ratios for all the (exclusive) measurementsdone in successive years, experiments use different BR to derive their cross-sections •  corresponding uncertainties were corrected for, or added if previously not taken into account • Some values required special care...

  8. Charm Cross Section Values after Corrections • Corrections range from 16% to 33% • Example : NA32, -Cu at 230 GeV : • neutral D : 6.3  0.3  1.2 b  6.6  0.3  1.0 b • charged D : 3.2  0.2  0.7 b  2.7  0.2 0.60.5b 20% change in thecharged / neutral ratio The total charm cross sections are 20% larger than the sum of the measured neutral and charged D meson values: (assuming that fragmentation functions are “universal”; following world averages from CLEO, ARGUS, H1, ZEUS, ALEPH, DELPHI, L3 and OPAL) C. Lourenço & H. K. Wöhri, Phys. Rep. 433 (2006) 127.

  9. Charm Cross Sections with pion Beams : Data vs. Pythia • In all our calculations we used: default Pythia version 6.326, except for: kT2 = (1.0 GeV/c)2 • With mC=1.5 GeV/c2 Pythia (LO calculation) underestimates the real cross-section • Curves must be scaled up by empirical K-factors; different for neutral and charged  Neutral D mesons Charged D mesons Pythia  K-factor

  10. Charged to Neutral D Meson Ratio Pythia assumes that the c quark fragments into the D singlet and the D* triplet mesons with equal probability (25%), resulting in m(D*0) < m(D+) + m(p-) = 0 Pythia Data / Pythia = 1.55 Data / Pythia = 1.12

  11. Correcting the “Charged / Neutral” Charm Ratio in Pythia PV : ratio of abundances of vector (triplet) states to the ones of singlet states D* / (D+D*) world average PV = 0.591±0.007 Pythia’s defaultfor heavy flavour e+e-, √s < 7 GeV DIS A e+e-, √s ~ 10.5 GeV: e+e- → Z0 p Hadro-production All w/o hadro-prod. All A. David, Phys. Lett. B644 (2007) 224 Pythia’s defaults for PV : 0.6 for strange particles 0.75 for charm and beauty PV Naïve spin counting, PV = triplet / (triplet + singlet) = 3 / (3+1) = 0.75 does not work; mass difference of D* and D cannot be neglected! with PV = PARJ(13) = 0.6 the ratio charged / neutral becomes 0.42

  12. PHENIX: pp [PRL97 (2006) 252002] STAR: pp, d-Au [PRL94 (2005) 062301] Elab = 158 GeV Elab = 400 GeV √s = 200 GeV Useful cross sections (ccbar) [b] 4.5 ± 20% 18 ± 5% 600 ± 40% Uncertainties estimated by varying the PDFs and the c quark mass Charm Cross Sections with proton Beams : Data vs. Pythia • Calculations done with the same settings as before, except PARJ(13) = 0.6

  13. PLB462 (1999) 225 88990 ± 460 D0 mesons D0→K and D0 →K D Meson Transverse Distributions in -A and p-A 320±26 D mesons p-Be, Al, Cu, W PRL 77 (1996) 2392 Pythia 6.326 with default settings and kT2 = 1.0 (GeV/c)2describes quite well these spectra(and also the xF distributions, not shown here)

  14. D Meson Pair Correlations : Available Data • We only compare Pythia’s calculations to “high statistics” data samples: • E791 : 500 GeV -C collisions;Eur. Phys. J. direct C1 (1999) 4 • Fully reconstructed both D mesons of 791±44 pairsAnalysis performed for events with both D mesons in -0.5 < y* < 2.5 • WA92:350 GeV -Cu collisions;Phys. Lett. B385 (1996) 487 Reconstructed one D meson with xF > 0 and the vertex of the second one (with any xF)475 pair events in full phase space • NA32 : 230 GeV -Cu collisions ; PLB257 (1991) 519 , PLB302 (1993) 112, PLB353 (1995) 547 • Purely topological approach; reconstructed ~500 events with two D mesons with xF > 0 Correlation variables studied:  = (D) – (Dbar), pT2(DDbar) = |pT(D) – pT(Dbar)|2, |pT2| = |pT2(D) – pT2(Dbar)| y = y(D) – y(Dbar),xF = xF(D) – xF(Dbar), xF(DDbar) M(DDbar) For each data set, a specific Pythia curve was prepared to reflect the experimental conditions

  15. D Meson Pair Correlations : Some Results y  pT2(DDbar) [(GeV/c)2] For easier comparison, curves and data points were normalised to the E791 data  Pythia describes reasonably well the correlation variables

  16. p-A Beauty Meson Production Cross Sections • Energy range : Elab = 286–920 GeV (fixed target)s = 630 GeV (UA1), 1.8 and 1.96 TeV (CDF) • Most experiments measured a B hadron mixture • Linear nuclear dependence assumed • The p-A measurements are not very consistent... Pythia p-A p-A pp

  17. ppbar p-A Beauty Cross Sections and Displaced J/y : Data vs. Pythia • Within a factor of 2, the calculation describes the HERA-B and CDF data points, four orders of magnitude apart ! At RHIC energies we get 2.5 mb • CDF Run II measured B by selecting displaced J/y Pythia withkT2 = 1.0 (GeV/c)2reproduces the pT spectrum over 3 orders of magnitude • See also FONLL calculations: PRL 95 (2005) 122001, JHEP 7 (2004) 33

  18. CDF, run IIpp s = 1.96 TeV |y(J/y)| < 0.6 PRD 71 (2005) 032001 Beauty Feed-down into the J/y Spectra Beauty production scales faster with energy than J/y production. The ratiowill be higher at the LHC than it is at CDF.  At the LHC, a significant fraction of the detected J/y mesons will be due to B meson decays (and, therefore, will not be suppressed)This fraction changes with pT and might also change from pp to Pb-Pb collisions, due to different nuclear dependences (even in the absence of “new physics”)  Good vertex detectors are crucial to understand J/y suppression in Pb-Pb collisions !

  19. Open Charm through Dimuons in NA60 : p-A at 400 GeV The intermediate mass dimuon region (1.2–2.1 GeV/c2) is compared to Drell-Yan dimuons plus open charm decays, normalised to the cross section derived from our compilation: sccp-Pb = 19.9 mb, including anti-shadowing (EKS98) c2 / ndf = 37 / 42 = 0.87 good description w/o any adjustments! (also for p-Be and p-In data) NA60 Drell-Yan

  20. Open Charm through Dimuons in NA60 : In-In at 158 GeV NA60 measures the offset of the (di)muon tracks w.r.t. the interaction point, thanks toa high granularity silicon pixel vertex tracker The measured IMR is compared to the sumof prompt dimuons and open charm decays The shape of the prompt spectrum is taken from the measured events in the f and J/y peaks; the charm shape is generated from Pythia events immersed in real data Dimuon mass window :1.16 < M < 1.56 GeV/c2 data c2 / ndf = 1.5 charm promptdimuons The fit to the In-In weighted offset spectrum results in a NN charm cross section of 9.5 ± 2.0 mb; this is a factor 1.9 ± 0.6 higher than expected from the previously shown compilation of charm cross sections, including EKS98 anti-shadowing, 5±1mb

  21. Including EKS98 shadowing. LHC values: NLO calculations Charm and Beauty Yields vs. Energy and Collision System Charm cross section at the LHC is higherby a factor ~ 10 w.r.t. RHIC energies andby a factor ~ 1000 w.r.t. SPS energies:s = 20 GeV sccpp ~ 5 mbs = 200 GeV sccpp ~ 600 mbs = 5.5 TeV sccpp ~ 6600 mb • Abundance of charm production at the LHC will allow us to make detailed studies of several topics, including charm thermalisation through elliptic flow measurements. Charm flow has been indirectly seen at RHIC using non-photonic electrons... PRL 98 (2007) 172301

  22. Charm Beauty Charm Beauty ALICE barrel ALICE muons ALICE barrel ALICE muons LHC : High Energies → Small x values [N. Carrer, A. Dainese, hep-ph/0311225] • Small x values probed: down to 5×10-6 in pp and to 10-5 in Pb-Pb, in the case of the ALICE detectors

  23. s=5.5 TeV pp at s=14TeV beauty Pb-Pb / pp charm Heavy Flavours at LHC Energies: Initial State Effects Nuclear shadowing leads to a suppression of heavy flavoured particles in p-A and A-A collisions: ~ 35% reduction of charm production and ~ 15% reduction of beauty, according to EKS98 It must be studied in p-A collisions Gluon saturation should lead to an increase of charm at low pT w.r.t. the standard DGLAP evolution [A. Dainese et al, J. Phys. G30 (2004) 1787] both effects are important at low pT(where most of the cross section sits) crucial to have good acceptance at low pT

  24. Heavy Quark Energy Loss at LHC Energies • Parton energy loss is expected to occur by: • medium-induced gluon radiation • collisions in the medium • It depends on the properties of the medium: • length, energy density, etc. • It is also expected depend on the colour factor and on the quark mass: • We will probe heavy quark energy loss through ratios of pT distributions, betweenPb-Pb and pp, between B and D mesons, etc • We should also do these studies using jets tagged by the presence of D or B mesons DE (L, eQGP) DEg > DEc~q > DEb RAAp < RAAD < RAAB PRL 98 (2007) 192301 To keep in mind:gluon saturation should induce changes between “baseline” pp and Pb-Pb data(Qs2~ A1/3)

  25. hep-ph/0601164 Heavy Flavour Production in ALICE • ALICE has a barrel system with high precisionvertexing, PID and electron identification (|h| < 0.9)and a forward muon spectrometer (h: 2.5–4.0), • down to low pT.Heavy flavour production can be studied: • In the electronic and muonic channels D, B  eX (mX) DDbar, BBbar eeX, mmX BBbar  and J/ BBbar J/ ee • By looking at em correlations • In several hadronic decay channels: D0  K , D±  K D0  Kpp, Ds  KKp, Ds    D*  D0p, Lc  pKpGood transverse impact parameter resolution to tag heavy-flavour decays ALICE PPR II, J. Phys. 32 (2006) 1295

  26. Abundant Heavy Flavour Production... is not always good Correlated dimuons Uncorrelated muon pairs Dimuon mass spectrumin the ALICE muon armin central Pb-Pb collisions at 5.5 TeV 2.5 < y < 4.0 pTm < 1 GeV/c p/K J/y cc total bb(+cc) bb y’ Besides the (very large) combinatorial background from p and K decays,there is also a rather large yield of muon pairs from uncorrelated charm decays  New source of background that must be subtracted (by event mixing) to have a good measurement of the charmonia resonances and of open beauty

  27. Towards Heavy Flavour Measurements in CMS Silicon tracking system with 3 pixel and 9 micro-strip layersAnalog readout  dE/dx in silicon  p/K/p separation up to 1–2 GeV/c 100×150 mm2 pixels: 2% occupancy even at dNch/dy = 5000  Identified particle spectra and yields of: s = 16 MeV s = 6 MeV L L dotted: generated solid: reconstructed

  28. Summary and Outlook We reviewed open charm and open beauty data that should be used to “calibrate” theoretical calculations before they are extrapolated to LHC energies(we will soon replace our Pythia curves by MNR NLO calculations) Heavy flavour production is very important to study several interesting Heavy-Ion physics questions, including gluon saturation, heavy quark energy loss, quarkonia suppression, etc We briefly discussed some of the physics opportunities in the Heavy Flavour sector at the LHC and the related detector capabilities In the next couple of years we will surely see Heavy Flavour production becominga main course in the physics menu of the LHC (Large Heavy-ion Collider)

  29. gluon radiation of the pair creation process gluon splitting flavour excitation Open Beauty contributions to dimuon mass spectrum • Angular coverage of the ALICE muon spectrometer: 2.5 < y < 4.0 • Different beauty production processes and decays contribute to different dimuon mass windows... • The low mass region gets many muon pairs from cascade decays of single B mesons: • At low masses (small opening angles) gluon splitting and flavour excitation are more important than pair creation pTm < 1 GeV/c2.5 < y < 4.0 Mmm [GeV]

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