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Heavy Flavours

Heavy Flavours. Federico Antinori INFN Padova - Italy. Introduction. Aim: introduction to heavy flavour production and nucleus-nucleus collisions open flavour only; for quarkonia: E. Scomparin Assume audience familiar with nucleus-nucleus basics I have left out some things, e.g.:

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Heavy Flavours

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  1. Heavy Flavours Federico Antinori INFN Padova - Italy

  2. Introduction • Aim: introduction to heavy flavour production and nucleus-nucleus collisions • open flavour only; for quarkonia: E. Scomparin • Assume audience familiar with nucleus-nucleus basics • I have left out some things, e.g.: • no detailed description of apparatus • no discussion of DD j correlation, intrinsic KT • ... • credits: A Dainese, M Mangano, E Quercigh Federico Antinori - Villa Gualino - May 2005

  3. Contents • Heavy Flavour Decays • Heavy Flavour Production in QCD • Heavy Flavour in p/p-A • Heavy Flavour Fragmentation • D* decays and leading D’s • Heavy Flavour at Tevatron • Heavy Flavour in pp, dAu at RHIC • Heavy Flavours in AA • SPS, RHIC • perspective for LHC • Finale Federico Antinori - Villa Gualino - May 2005

  4. Heavy Flavour Decays

  5. Some zoology... • Lower mass heavy flavour hadrons decay weakly • t ~ ps • ct ~ 100’s µm • weakly decaying states from PDG 2004 summary tables: Federico Antinori - Villa Gualino - May 2005

  6. In UR limit b ~ Lorentz invariant: ... so b ~ independent of g if cos qCM distribution is flat: so, in space, in projection: so: Impact parameter ~ ct primary vertex decay length = L q decay vertex impact parameter = b y d j x b Federico Antinori - Villa Gualino - May 2005

  7. Weak decays of charm W- W+ W+ c c b s’ c s’ e+ µ+ u ne nµ d’ • typically: • large branching ratio to kaons: • D+: • D+  K-+X BR ~ 28 % • “golden” channel: D+ K-p+p+ BR ~ 9% • D0: • D0 K-+X BR ~ 50% • “golden” channels: D0 K-p+ BR ~ 4% ; D0 K-p+p+p- BR ~ 7% • W± branchings: • large semileptonic branching ratio, varies with heavy flavour particle, typical ~ 10% ~ 10% heavy flavour hadrons give in final state an e± (and ~ 10% a µ±) (and with a respectable pT...) C = “Cabibbo angle” (similarly: )

  8. Standard experimental tools WA92: Si µstrips primary vertex decay length = L q decay vertex impact parameter = b [Adamovich et al.: NIM A 379 (1996) 252] • Silicon vertex detectors: • so: tracks from heavy flavour weak decays typically “miss” primary vertex by ct ~ 100’s µm • impact parameter resolutions of typical heavy flavour apparatus ~ 10’s µm • e± and/or µ ± identification • charged kaon identification Federico Antinori - Villa Gualino - May 2005

  9. Heavy Flavour Production in QCD

  10. Heavy Flavour hadro-production in pQCD a=q Q b=q Q • Factorization: (at sufficiently large Q2) hadron charmed hadron hadron parton distribution functions xa = momentum fraction of parton a in hadron A cross-section at parton level e.g.: fragmentation z = fraction of c momentum to hadron D cross-section at hadron level Federico Antinori - Villa Gualino - May 2005

  11. factorization implies: • PDFs can be measured with one reaction... • say: Drell-Yan: A+B  e+e- + X ... and used to calculate a different one • say: heavy-flavour production • fragmentation independent of the reaction (e.g.: same in pp, e+e-) Federico Antinori - Villa Gualino - May 2005

  12. Parton Distribution Functions • The PDFs vary depending on the momentum transfer scale Q2 • Intuitively: higher Q2 -> higher resolution high-x parton -> lower-x partons • The Q2 evolution of the PDFs can be calculated in pQCD • Altarelli-Parisi evolution (DGLAP) Federico Antinori - Villa Gualino - May 2005

  13. Leading-order (LO) q Q Q g g Q g q g Q Q Q Q g Q g • Relevant diagrams: pair creation • qq QQ (quark-antiquark annihilation) • gg QQ (gluon-gluon fusion) Federico Antinori - Villa Gualino - May 2005

  14. A few results • the partonic cross-section decreases with energy • faster for qq than for gg (which therefore is expected to dominate, except near threshold) • the parton luminosities near threshold increase with energy, the cross section increases with the energy of the hadron-hadron collision • the pair cross section is proportional to: y (y): rapidity of Q (Q) • Q and Q therefore expected to be close in y • Experimentally: EHS, 360 GeV p-p  DDX Federico Antinori - Villa Gualino - May 2005 [EHS: PLB 123 (1983) 98]

  15. Next-To-Leading-Order (NTLO) Q Q Q Q Q Q • in absolute value, LO cross sections are typically underestimated by factor 2.5 - 3 (“K factor”) • at NTLO: additional diagrams, such as: higher order corrections to pair creation flavour excitation gluon splitting Federico Antinori - Villa Gualino - May 2005

  16. the agreement with experiment for the total cross-section is good (within large bands...) • e.g.: charm cross section at fixed target: [Mangano: hep-ph/9711337] Federico Antinori - Villa Gualino - May 2005

  17. results depend on the values of: • mc, µR (renormalization scale), µF (factorization scale) • the result of an exact calculation would be independent of the choice of the scale parameters µR, µF • the residual scale dependence is a measure of the accuracy of the calculation • e.g.: for b production at Tevatron (µR=µF=µ): [Mangano: hep-ph/9711337]

  18. Q Q Q Q • it is important to match the PDFs with the order of the calculation. • e.g. one must avoid double counting: • at LO: • at NTLO: “intrinsic flavour” “flavour excitation” Federico Antinori - Villa Gualino - May 2005

  19. Heavy Flavour in p/p-A

  20. Nuclear shadowing antishadowing shadowing SPS RHIC LHC • PDFs in the nucleus different from PDFs in free proton • R = ratio of nuclear to nucleon PDFs • from Deep Inelastic Scattering (e-+p; e-+A), Drell-Yan (p+p, p+A -> l +l -+X) e.g.: R for gluons vs gluon momentum fraction x from EKS parametrization [Eskola et al.: EPJ C9 (1999) 61] • typical x for cc production (y 0) • x  10-1 @ SPS • x  10-2 @ RHIC • x  a few 10-4 @ LHC Federico Antinori - Villa Gualino - May 2005

  21. Nuclear dependence • From pQCD one expects the cross section for production off nuclei to increase like number of nucleon-nucleon collisions (“binary collision scaling”) • proportional to number of nucleons (for min. bias collisions): • modulo shadowing effects, expected to be small • Experimentally: not far... e.g. WA82: • D production in p-+W/Si at SPS (340 GeV beam momentum) • (relatively) central production with a =1 “Feynman’s x” Federico Antinori - Villa Gualino - May 2005

  22. Caveats... with • i) a = 1 does not work down to pp! • e.g.: MacDermott & Reucroft [PLB 184 (1987) 108] compare pA results with earlier hydrogen data from NA27, good agreement using: • note: similar situation for light flavours! systematic study by Barton et al. [PRD 27 (1983) 2580], for various reactions at 100 GeV FT e.g.: central for production of p, K, p from p on nuclear targets: Federico Antinori - Villa Gualino - May 2005

  23. ii) lower a at large xF? • early beam dump experiments, sensitive at large xF (max acceptance for xF 0.5) (in tracking experiments, typically max. acceptance for xF 0.2) e.g. WA78 [Cobbaert et al.: PLB 191 (1987) 456] a for muons escaping dump (p-A at 320 GeV FT ): • note: a is known to decrease with xF for light hadrons [Barton et al.: PRD 27 (1983) 2580] Federico Antinori - Villa Gualino - May 2005

  24. Heavy Flavour Fragmentation

  25. Fragmentation • String fragmentation model: (e.g. [PYTHIA hep-ph/0308153]) • as coloured quarks fly away, energy is stored in the field: • above a certain distance it is cheaper to break the string by creating a new qq pair than to keep increasing the distance • the string snaps, e.g.: the heavy quark ends up “hadronising” together with a light antiquark • the newly created quarks are of course light • estimated ratios: u : d : s : c  1 : 1 : 0.3 : 10-11 • no heavy flavour production in string breaking! k 1 GeV/fm Federico Antinori - Villa Gualino - May 2005

  26. Fragmentation function Peterson (e = 0.015) Colangelo-Nason (a = 0.9, b=6.4) • c  D, D takes fraction z of c momentum • fragmentation function: DD/c(z) • depends only on fraction z • e.g.: Peterson Colangelo-Nason e.g.: (parameters from fits to charm production at LEP) Federico Antinori - Villa Gualino - May 2005

  27. Q Q e- Z0 e+ • How to measure the fragmentation function? • we don’t measure the original Q momentum ... • but in e+e- we do know the Q energy (by energy conservation!) • e.g.: • fragmentation functions are usually extracted from e+e- measurements and then used for other collisions Federico Antinori - Villa Gualino - May 2005

  28. e.g.: fits to charm x = 2E/s distributions in e+e-: [Cacciari & Greco: PRD55 (1997) 7134] • very similar parameters at the two energies (as expected) Peterson fragmentation s = 10.6 GeV (ARGUS) s = 91.2 GeV (OPAL) e = 0.015 (OPAL) e = 0.019 (ARGUS) Federico Antinori - Villa Gualino - May 2005

  29. Q Q • like for the PDFs, the fragmentation function has to be matched to order of pQCD calculation • e.g. at NTLO the Q can radiate: • so final energy before non-perturbative part of fragmentation lower than at LO • harder fragmentation at NTLO • at NTLO: e 0.015 • at LO: e 0.06 (e.g.: [Cacciari & Greco: PRD55 (1997) 7134]) Peterson fragmentation e = 0.015 (NTLO) e = 0.06 (LO) Federico Antinori - Villa Gualino - May 2005

  30. D* decays and leading D’s

  31. D* decays • Most of the D mesons (from spin counting, ~ 75%) are not directly produced at hadronization, but in D* decays • D±, D0 J=0 • D*±, D*0 J=1 • Due to fine tuning of the values of the masses: • m(D±) + m(p0) < m(D*±) • m(D0) + m(p±) < m(D*±) • m(D0) + m(p0) < m(D*0) but... • m(D±) + m(p±) > m(D*0) • ... the light quark content of charged D is preserved also in case of resonance decays: • a D0(cu) can originate from either D*0(cu) or D*+(cd) • a D+(cd) can only originate from a D*+(cd) Federico Antinori - Villa Gualino - May 2005

  32. Leading effects in D production [WA82: PLB 305 (1993) 402] • From perfect factorization one would expect: • fractions of different charm hadrons independent of collision system • as many D- as D+ • but with a p- beam, at forward xF : D- > D+ • e.g. WA82, p-+W : • excess particularly pronounced at large xF • if c can hadronize not only by fragmentation, but also by valence quark recombination (sounds familiar?) then ... with p- (ud) beam, c D-(cd) >c D+(cd) (especially at large xF...) • can’t do the same with D0(cu), since, as just discussed, it could come from D*+(cd) • Qualitatively reproduced by PYTHIA

  33. ... so factorization not the full story... Federico Antinori - Villa Gualino - May 2005

  34. D0/D+ ratio at LEP • D*0 and D*+ both decay strongly into D’s, but: • D*+ can decay to both D0 and D+ • D*0 can only decay to D0 • From spin degeneracy one expects: D0 : D+ : D*0 : D*+ = 1 : 1 : 3 : 3 • ... and therefore a large D0/D+ ratio • using the experimental branching ratios: • but experimentally, at LEP: a puzzle.... [ALEPH: EPJ C16 (2000) 597] Federico Antinori - Villa Gualino - May 2005

  35. Heavy Flavour at Tevatron

  36. Beauty at Tevatron • Discrepancy between pQCD and data seems to have disappeared... • from... a factor 5.5 (but only 1.6 s ...) • to... Run 0 [CDF: PRL 68 (1992) 3403] Spectrum of J/y from secondary B decays Run II [Cacciari et al: JHEP 0407 (2004)] Federico Antinori - Villa Gualino - May 2005

  37. From run I on, important improvements in accuracy: • experiment (vertex detectors, high statistics) • prediction (post-HERA PDF sets) • Levels of stability over time: • no large room for new physics any more... • for more see, e.g.: [Cacciari et al: JHEP 0407 (2004) 033, Cacciari: hep-ph/0407187, Mangano: hep-ph/0411020] Data Predictions from [Cacciari et al: JHEP 0407 (2004) 033] Federico Antinori - Villa Gualino - May 2005

  38. What about charm? • Nice data from CDF run II • roughly in agreement with full pQCD calculation (though prediction somewhat low) [CDF: Phys.Rev.Lett. 91 (2003) 241804] • A curiosity (?): good agreement between data and prediction for bare quark [Vogt: talk at SQM 2004] Federico Antinori - Villa Gualino - May 2005

  39. Heavy Flavour in pp, dAu at RHIC

  40. pp, dAu at RHIC • Two types of measurements: • full reconstruction of D, D* decays (STAR) • subtraction of non-charm components from electron spectra (STAR, PHENIX) Federico Antinori - Villa Gualino - May 2005

  41. Full reconstruction in dAu (STAR) • Experimental technique: • tracks from TPC • K, p identification from dE/dx (at low pT) • no separation of D decay vertex • large combinatiorial background evaluated by event mixing and subtracted Extracted pT spectrum [STAR: J.Phys. G30 (2004) 809] Federico Antinori - Villa Gualino - May 2005

  42. Non-photonic electrons in pp, dAu • Identified electron spectra • STAR: dE/dx in TPC (+ TOF cuts at low pT) • PHENIX: combined RICH and E/p (with E from EM cal) • Rejection of non-charm electrons • Main source of electrons: “photonic” • g e+e- conversions • Dalitz decays p0 e+e-g • Dalitz decays h e+e-g • STAR: • rejected by full invariant mass analysis of e+e- combinations • PHENIX: • pp run: estimated by simulation and subtracted • dAu run: measured by “converter method” and subtracted • Other sources of non-charm electrons: • w, r, j, K decays • estimated by sim. and subtracted (in both STAR and PHENIX) (“internal conversions”)

  43. RHIC pp, dAu vs pQCD • direct reconstruction • an excess, again? • “non-photonic” electrons • much less evident... band: pQCD charm + beauty PHENIX: pp STAR: dAu (scaled to pp by number of binary collisions) [Cacciari, Nason, Vogt: hep-pe/0502203] Federico Antinori - Villa Gualino - May 2005

  44. ... the situation is somewhat confusing ... • bare c ds/dpT must be multiplied by 4 to reproduce STAR d-Au D data CDF STAR M. van Leeuwen - STAR plot by R. Vogt • bare c ds/dpT (upper curves) agrees reproduces CDF D data with no rescaling...  good measurement of pp baseline at RHIC, LHC essential ! Federico Antinori - Villa Gualino - May 2005

  45. Heavy Flavours in AA

  46. c, b as AA probes • c, b produced in early stages of collision, then conserved (neglecting annihilation)  ideal probes of bulk, strongly interacting phase • e.g.: energy loss? • thermal production? • no extra production at hadronization  ideal probes of fragmentation • independent string fragmentation vs recombination • + important measurement for “practical” reasons • open QQ production (not Drell-Yan) natural normalization for QQ studies • B meson decays non negligible source of non-prompt J/y QUARK-GLUON PLASMA AND PRODUCTION OF LEPTONS, PHOTONS AND PSIONS IN HADRONIC COLLISIONS E.Shuryak, Yadernaya Fizika 28 (1978) 403 Federico Antinori - Villa Gualino - May 2005

  47. Heavy flavour production in AA • binary scaling: can be broken by: • initial state effects (modified PDFs) • shadowing • kT broadening • gluon saturation (colour glass) (concentrated at lower pT) • final state effects (modified fragmentation) • parton energy loss • violations of independent fragmentation (e.g. quark recombination) (at higher pT) Federico Antinori - Villa Gualino - May 2005

  48. Heavy Flavours at SPS, RHIC

  49. Excess of charm-like dimuons (NA50) Peripheral Central • Excess of dimuons over known sources in the mass region below the J/y, especially pronounced in central events • Charm enhancement? (~ x 3 required) • Thermal dimuons?  NA60 repeating measurement with a pixel vertex detector Federico Antinori - Villa Gualino - May 2005

  50. but at RHIC ... 1/TABEdN/dp3 [mb GeV-2] PHENIX • “non photonic” e± • subtracted by converter method • only expected source is c semi-leptonic decay • ~ agreement with Ncoll-scaled Phenix pp reference • (deviates at high pT) • no sign of enhancement! Federico Antinori - Villa Gualino - May 2005

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