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Andr é Mischke for the STAR Collaboration

Amsterdam. Heavy-flavor particle correlations in STAR via electron azimuthal correlations with open charm mesons. Andr é Mischke for the STAR Collaboration. Quark Matter  Jaipur  February 4-10, 2008. Outline. Motivation Correlation technique Gluon splitting process at RHIC

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Andr é Mischke for the STAR Collaboration

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  1. Amsterdam Heavy-flavor particle correlations in STARvia electron azimuthal correlations with open charm mesons André Mischke for the STAR Collaboration Quark Matter  Jaipur  February 4-10, 2008

  2. Outline • Motivation • Correlation technique • Gluon splitting process at RHIC • - comparison to MC@NLO simulations • Data analysis in p+p collisions • - relative Be contribution • Summary Andre Mischke (UU)

  3. PRL98, 192301 (2007) Motivation • Study dynamical properties of the QGPe.g., initial gluon density, drag coefficient • Heavy quarks • - primarily produced in initial state of the collision  well calibrated probes • - expected to lose less energy due to suppression of small angle gluon radiation (so-called”dead-cone effect”) • Surprise in central Au+Au:Electrons from D and B decays are strongly suppressed • Models implying D and B energy loss are inconclusive yet • Goals • Access to underlying production mechanisms • Separate D and B contribution experimentally D/B crossing point M. Cacciari et al., PRL95, 122001 (2005) Andre Mischke (UU)

  4. trigger side c g g c 3.83% 54% ~10% charm production c  0 c g g g g probe side flavor creation (LO) gluon splitting (NLO) Correlation technique • Identification and separation of charm and bottom production events using their decay topology and azimuthal angular correlation of their decay products • electrons from D/B decays are used to trigger on charm/bottom quark pairs • associate D0 mesons are reconstructed via their hadronic decay channel (probe) Andre Mischke (UU)

  5. + e- K- e D0 D*0 B- unlike-sign pairs  away-side correlation like-sign pairs  near-side correlation b b B+ D0 Near- and away-side correlation peak expected for B production - K+ Electron tagged correlations:bottom production Charge-sign requirement on trigger electron and decay Kaon gives additional constraint on production process Andre Mischke (UU)

  6. like-sign e-K pairs unlike-sign e-K pairs LO PYTHIA 3<pTtrg<7 GeV/c LO PYTHIA simulations • Near-side • B decays (dominant) • Away-side • charm flavor creation (dominant) • small B contribution • Away-side • B decays (dominant) • small charm contribution Andre Mischke (UU)

  7. PYTHIAcharm production STAR preliminary NLO Process: Gluon splitting • FONLL/NLO calculations only give single inclusive distribution  no correlations • PYTHIA is not really adequate for NLO predictions • STAR measurement of D* in jet  access to charm content in jets • Gluon splitting rate consistent with pQCD calculation •  Small contribution from gluon splitting at top RHIC energy E. Norrbin & T. Sjostrand, Eur. Phys. J. C17, 137 (2000) Mueller & Nason PLB 157, 226 (1985) P29: X. Dong, Charm Content in Jets Andre Mischke (UU)

  8. MC@NLO LO PYTHIA like-sign e-K pairs 3<pT<7 GeV/c Δ(c,c) Δ(e,D0) MC@NLO predictions for charm production • NLO QCD computations with a realistic parton shower model • Away-side peak shape: remarkable agreementbetween LO PYTHIA and MC@NLO • Near-side: GS/FC  5% small gluon splitting contribution  in agreement with STAR measurement • S. Frixione, B.R. Webber, JHEP 0206 (2002) 029 • S. Frixione, P. Nason, and B.R. Webber, JHEP 0308 (2003) 007 • private code version for charm production Andre Mischke (UU)

  9. advantage BEMC e- TPC K- + BEMC STAR experiment Solenoidal Tracker at RHIC Large acceptance magnetic spectrometer • Energy measurement • - Barrel EMC • fully installed and operational, || < 1 • Pb/scintillator (21 X0) • dE/E ~ 16%/E • Shower maximum detector • PID and tracking • - TPC • || < 1.5 • p/p = 2-4% • dE/dx/dEdx = 8% • - Magnet • 0.5 Tesla DatasetRun6p+p at s = 200 GeV, L = 9 pb-1 High ET triggerenergy threshold 5.4 GeV Andre Mischke (UU)

  10. aftercut on p/E and shower shape electron candidates dE/dxcut hadrons Electron identification • Quality cuts • well developed shower in EM calorimeter • 0. < p/Etower< 2. • 3.5 < dE/dx < 5.0 keV/cm (pT dependent) • High electron purity up to high-pT •  Clean electron sample dE/dx (keV/cm) purity (%) Andre Mischke (UU)

  11. e+ (global track) e- (assigned as primary track) e- (primary track) dca  Photonic electron background • Most of the electrons in the final state are originating from other sources than heavy-flavor decays • Dominant photonic contribution • gammaconversions • 0 and  Dalitz decays • Exclude electrons with low invariant mass minv< 150 MeV/c2 •  Non-photonic electron excess at high-pT • Photonic background rejection efficiency is 70% Andre Mischke (UU)

  12. w/o electron trigger w/ non-photonic electron trigger STAR preliminary dn/dm combinatorial background is evaluated using like-sign pairs PRL 94, 062301 (2005) position: 1892 ± 0.005 GeV/c2 width: 16.2 ± 4.7 MeV/c2 (K) invariant mass distribution D0+D0 • D0 reconstruction: dE/dx cut (±3) around Kaon band • Significant suppression of combinatorial background: factor 200 • S/B = 14% and signal significance = 3.7 Andre Mischke (UU)

  13. like-sign e-K pairs: (e- D0) + (e+D0) p+p at s = 200 GeV L = 9 pb-1 statistical errors only Azimuthal correlation of non-photonic electrons and D0 mesons expected D0/e ratio for charm flavor creationand a track reconstruction efficiency of 80-90% • First heavy-flavor correlation measurement at RHIC • Near- and away-side correlation peak  yields are about the same Andre Mischke (UU)

  14. Relative Be contribution like-sign e-K pairs • Model uncertainties not included yet • Good agreement between different analysesP215: S. Sakai, e-h correlation in p+p • Data consistent with FONLL within errors essentially from B decays only 75% from charm 25% from beauty Comparable D and B contributions  Au+Au: suggests significant suppression of non-photonic electrons from bottom in medium Andre Mischke (UU)

  15. Summary and conclusions • First heavy-flavor particle correlation measurement in p+p collisions at RHIC • MC@NLO simulations: Small gluon-splitting contribution • Azimuthal correlation of non-photonic electrons and D0 mesons • access to production mechanisms •  allows separation of charm and bottom production events • efficient trigger on heavy-quark production events • significant suppression of the combinatorial background in D0 reconstruction • Contribution to non-photonic electrons from bottom is significant (50% at pT = 3-7 GeV/c) • Correlation technique is a powerful tool for comprehensive energy-loss measurements of heavy-quarks in heavy-ion collisions (e.g. IAA) Andre Mischke (UU)

  16. The STAR collaboration 52 institutes from 12 countries, 582 collaborators Andre Mischke (UU)

  17. Backup slides Andre Mischke (UU)

  18. D0D*- cross section measurement at the Tevatron D0 or D+  D*- B. Reisert et al., Beauty 2006, Nucl. Phys. B (Proc. Suppl.) 170, 243 (2007) • Within errors near- and away-side yields are the same  gluon splitting as important as flavor creation • Near-side yield: PYTHIA underestimates gluon splitting Andre Mischke (UU)

  19. PYTHIA event generator • Parameter settings • version: 6.222 (Jan. 2004) • MSEL = 4 or 5 charm or bottom • PMAS(4,1) = 1.3 or 4.5 mc or mb • PARP(91) = 1.5 <kT> • PARP(31) = 3.5 k factor • MSTP(33) = 1 common k factor • MSTP (32) = 4 Q2 scale • MSTP(51) = 7 CTEQ5L PDF • PARJ(13) = 0.594 D/D* spin factor • CKIN(3) = 1 • PARP(67) = 4 ISR+FSR • MSUB(81)= MSUB(82)= sub-processes • MSUB(84)= 1 • kt ordering in shower • String hadronization • default FF (Peterson) • B mixing included Andre Mischke (UU)

  20. MC@NLO event generator • Version 3.3 (Dec. 2006) • CTEQ6M PDF • HERWIG event generator (version 6.510, Oct. 2005) • - parton showering • - hadronization • - particle decays • Parameter settings • mc = 1.55 GeV/c2 • mb = 4.95 GeV/c2 HERWIG • Angular-ordered shower • Cluster hadronization Andre Mischke (UU)

  21. Model comparison Andre Mischke (UU)

  22. py pTelectron  px  bin pThadron-pair D0 yield versus (e, hadron pair) • Calculate  between non-photonic electron trigger and hadron pair pT • Extract D0 yield from invariant mass distribution for different  bins Andre Mischke (UU)

  23. STAR Preliminary D* in jet measurement Run V p+p, jet patch triggered data:1.7 M jets > 8 GeV/c • Magnitude at high z region is suppressed due to trigger, and it is consistent with MC simulation for only direct flavor creation process • Excess at low z region is expected to be from gluon splitting process Andre Mischke (UU)

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