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Charm and Electrons in

Charm and Electrons in. Thomas Ullrich, STAR/BNL International Workshop on Electromagnetic Probes of Hot and Dense Matter ECT, Trento June 8, 2005. Outline. STAR’s Heavy Flavor Program Detector capabilities Experimental techniques Open Charm (and Beauty) Production

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Charm and Electrons in

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  1. Charm and Electrons in Thomas Ullrich, STAR/BNL International Workshop on Electromagnetic Probes of Hot and Dense Matter ECT, Trento June 8, 2005

  2. Outline • STAR’s Heavy Flavor Program • Detector capabilities • Experimental techniques • Open Charm (and Beauty) Production • Non-photonic electrons • p+p: the reference • d+Au: cold nuclear matter effects • Au+Au: ( QM’05) • D mesons • d+Au: charm cross-section • Au+Au: ( QM’05) • Thermalization of heavy quarks ? • Au+Au: v2 of non-photonic electrons • Quarkonia: J/Y and  • Summary and Outlook

  3. Detecting D-Mesons via Hadronic Decays • Hadronic Channels: • D0  K(B.R.: 3.8%) • D K p(B.R.: 9.1%) • D*±D0π (B.R.: 68%  3.8% (D0  K) = 2.6%) • D0  K p r(B.R.: 6.2%  100% (rp+p-) = 6.2%) • Lc p K p (B.R.: 5%)

  4. Detecting D-Mesons via Hadronic Decays • TPC: • High tracking efficiency for tracking hadrons (~90%) • dp/p ~ 1% at 1 GeV/c • large acceptance |h|<1 • PID (dE/dx) limits: • p up to 1 GeV/c • K, p up to 0.7 GeV/c • SVT: • current vertex’ing performance not sufficient to resolve typical charm secondary vertices (ct ~ 120(D0) - 315(D)mm)  background  • Hadrons in STAR: • TPC: tracking, PID • SVT: vertex’ing, PID • ZDC/CTB: centrality/trigger • Current analyses are based on TPC alone

  5. Identify charged daughter tracks through energy loss in TPC Alternatively at high pT use h and assign referring mass (depends on analysis) Produce invariant mass spectrum in same event Obtain background spectrum via mixed event Subtract background and get D spectrum Often residual background to be eliminated by fit in region around the resonance General Techniques for D Reconstruction D0 D* D0 Exception D*: search for peak around m(D*)-m(D0) =0.1467 GeV/c2

  6. Detecting Charm/Beauty via Semileptonic D/B Decays • Semileptonic Channels: • c  e+ + anything (B.R.: 9.6%) • D0  e+ + anything(B.R.: 6.87%) • D e + anything(B.R.: 17.2%) • b  e+ + anything (B.R.: 10.9%) • B e + anything(B.R.: 10.2%)  single “non-photonic” electron continuum • “Photonic” Single Electron Background: • g conversions (p0 gg) • p0, h, h’ Dalitz decays • r, f, … decays (small) • Ke3 decays (small)

  7. Detecting Charm/Beauty via Semileptonic D/B Decays • Electrons in STAR: • TPC: tracking, PID • BEMC (tower, SMD): PID • EEMC (tower, SMD): PID • ToF patch: PID

  8. electrons hadrons Electron ID in STAR – EMC • TPC for p and dE/dx • e/h ~ 500 (pT dependent) • Tower E  p/E • e/h ~ 100 (pT dependent) • Shower Max Detector (SMD) shape to reject hadrons • e/h ~ 20 • e/h discrimination power ~ 105 Works for pT > 1.5 GeV/c

  9. Electron ID in STAR – ToF Patch MRPC – ToF (prototype): Df  p/30 -1 < h < 0 electrons Electron identification: TOF |1/ß-1| < 0.03 TPC dE/dx electrons

  10. Inclusive  non-photonic spectra : How to assess photonic background? PHENIX 1: cocktail method PHENIX 2: converter method STAR: measurement of main background sources Inclusive Single Electrons p+p/d+Au ToF + TPC: 0.3 GeV/c < pT < 3 GeV/c TPC only: 2 < pT < 3.5 GeV/c EMC + TPC: pT > 1.5 GeV/c

  11. Opening Angle Invariant Mass Square  conversion and 0 Dalitz decay reconstruction efficiency : ~60% at pT>1.0 GeV/c Signal Rejected Photonic Single Electron Background Subtraction in pp and dAu • Method: • Select an primary electron/positron (tag it) • Loop over opposite sign tracks anywhere in TPC • Reject tagged track when m < mcut ~ 0.1 – 0.15 MeV/c2 • Cross-check with like-sign • Rejection Efficiency: • Simulation/Embedding • background flat in pT • weight with measured p0 spectra (PHENIX) •  conversion and 0 Dalitz decay reconstruction efficiency ~60% • Relative contributions of remaining sources: PYTHIA/HIJING + detector simulations

  12. Photonic Single Electron Background Subtraction Excess over background pT dependent hadron contamination (5-30%) subtracted

  13. Non-Photonic Single Electron Spectra in p+p and d+Au

  14. hadrons Nuclear Effects RdAu ? • Nuclear Modification Factor: • Within errors compatible with RdAu = 1 … • … but also with RdAu(h) • NOTE: RdAu for a given pT comes from heavy mesons from a wide pT rangep(D) > p(e) (~ 1.5-3)  makes interpretation difficult

  15. D0 Mesons in d+Au • Mass and Width consistent • with PDG values considering • detector effects: • mass=1.867±0.006 GeV/c2; • mass(PDG)=1.8645±0.005 GeV/c2 • mass(MC)=1.865 GeV/c2 • width=13.7±6.8 MeV • width(MC)=14.5 MeV

  16. Obtaining the Charm Cross-Section scc • From D0 mesons alone: • ND0/Ncc ~ 0.540.05 • Fit function from exponential fit to mT spectra • Combined fit: • Assume D0 spectrum follows a power law function • Generate electron spectrum using particle composition from PDG • Decay via routines from PYTHIA • Assume: dN/dpT(D0, D*, D, …) have same shape only normalization • In both cases for d+Au  p+p: • sppinel = 42 mb • Nbin = 7.5  0.4 (Glauber) • |y|<0.5 to 4p: f = 4.70.7 (PYTHIA) • RdAu = 1.3  0.3  0.3

  17. Charm Cross-Section scc • pp Charm Cross-Section • From D0 alone: • scc = 1.3  0.2  0.4 mb • From combined fit: • scc = 1.4  0.2  0.4 mb

  18. pp pp Discrepancy between STAR and PHENIX ? STAR from d+Au: scc = 1.4  0.2  0.4 mb (PRL94,062301) PHENIX from p+p (preliminary): scc = 0.709  0.085 + (+0.332,-0.281) mb PHENIX from min. bias Au+Au: scc = 0.622  0.057  0.160 mb (PRL94,082301) Reality check: 1.4  0.447 mb and 0.71  0.343 mb are not so bad given the currently available statistics (soon be more!) SPS, FNAL (fixed target) and ISR (collider) experiments

  19. 90% 15% Discrepancy between STAR and PHENIX ? Combined fit of STAR D0 and PHENIX electrons: No discrepancy: scc=1.1 0.1  0.3 mb STAR: PRL 94, 062301 (2005) PHENIX p+p (QM04): S. Kelly et al. JPG30(2004) S1189

  20. Consequences of High Cross-Section: J/Y Recombination Statistical model (e.g. A. Andronic et. al. PLB 571,36(2003)) : Largecc yield in heavy ion collisions • J/Y production through recombination • possible J/Yenhancement • In stat models: scc typically from pQCD calculations (~390 mb) • STAR scc much larger enhancement (~3-4) for J/Y production in central Au+Au collisions • PHENIX’s upper limit would invalidate the expectation from large scc ?! Δy = 1 Δy = 2 Δy = 3 Δy = 4

  21. NLO/FONLL • Recent calculations in NLO (e.g. R. Vogt et al. hep-ph/0502203) • Calculations depend on: • quark mass mc • factorization scale mF (typically mF = mc or 2 mc) • renormalization scale mR (typically mR = mF) • parton density functions (PDF) • Hard to obtain large s with mR = mF (which is used in PDF fits) • Fixed-Order plus Next-to-Leading-Log (FONLL) • designed to cure large logs for pT >> mc where mass is not relevant • K factor (NLO  NNLO) ? from hep-ph/0502203

  22. NLO/FONLL • For pT spectra m2 mT2 • for s calculations m2 m2 • pT integrated s < direct calculated s • FONLL higher over most pT than NLO • Choice of FF plays big role • Uncertainty bands: • reflect uncertainties in m and mc

  23. Charm Total Cross Section Can we confirm or rule out Cosmic Ray experiments? (Pamir, Muon, Tian Shan) under similar conditions? NPB (Proc. Suppl.) 122 (2003) 353 Nuovo Ciment. 24C (2001) 557 X. Dong USTC PHENIX,STAR: stat. error only • NLO calculations under-predict current scc at RHIC • More precise data is needed  high statistics D mesons in pp

  24. Comparison: Non-Photonic Electrons with NLO • FONLL calculations: • Charm: • scaled by sSTAR/sFONLL • Bottom: • Can be estimated from fit of sum to data (numbers soon) • Errors used: data + FONLL uncertainty bands Plenty of room for bottom !!!

  25. High-pT D0-Meson Spectra in d+Au • How is it done ? • Assumptions: same shape of D0, D*, D spectra • D0 K  defines low pT points • D0 K  r defines one high-pT point • Combined allow power law fit • Allows to move D* and D spectra into place • Cross-check with known ratios Problem: D*/D0 and D/ D0 not well known (pT, s dependent ?) Note: spectrum depends on one point:D0 K  r

  26. High-pT D-Meson Spectra in d+Au • Headache: Spectra very hard (too hard) • NLO: fragmentation function d function (Peterson FF needs ec = eb) ? • Yield at 10 GeV/c only factor 3 below CDF (LO/NLO ~ 10) ? Intensive systematic studies of D0 K  rof many people over many month …

  27. High-pT D-Meson Spectra in d+Au • Until we found the problem … • subtle effect  after correction no significant signal D0 K  r •  “combined” low to high-pT D0 spectra is gone Note:D* itself is still valid!!! Now a “standalone” spectra. Doesn’t affect possibility of studying RAA in Au+Au Upper limits from D0 K  (90% CL)

  28. Strong Elliptic Flow at RHIC • Strong elliptic flow at RHIC (consistent with hydro limit ?) • Scaling with Number of Constituent Quarks (NCQ) • partonic degrees of freedom !? • (v2/n) vs. (pT/n) shows no mass and flavor dependence • Strong argument for partonic phase with thermalized light quarks • What’s about charm? • Naïve kinematical argument: need Mq/T ~ 7 times more collisions to thermalize • v2 of charm closely related to RAA

  29. Charm Elliptic Flow from the Langevin Model • Diffusion coefficient in QGP: D = T/Mh (h momentum drag coefficient) • Langevin model for evolution of heavy quark spectrum in hot matter • Numerical solution from hydrodynamic simulations • pQCD gives D(2pT)  6(0.5/as)2 AMPT: (C.M. Ko) ← s=10 mb ← s=3 mb

  30. Charm Elliptic Flow through Resonance Effects • Van Hees & Rapp, PRC 71, 034907 (2005) • Assumption: survival of resonances in the QGP • Introducing resonant heavy-light quark scattering • heavy particle in heat bath of light particles (QGP) + fireball evolution time-evolved c pT spectra in local rest frame “Nearly” thermal: T ~ 290 MeV Including scalar, pseudoscalar, vector, and axial vector D-like-mesons gives: σcq→cq(s1/2=mD)≈6 mb Cross-section is isotropic  the transport cross section is 6 mb, about 4 times larger than from pQCD t-channel diagrams

  31. How to Measure Charm v2 • Best: D mesons  need large statistics, high background  not yet • Alternative: Measure v2 of electrons from semileptonic charm decays • Emission angles are well preserved above p = 2 GeV/c • 2-3 GeV Electrons correspond to ≈3-5 GeV D-Mesons

  32. Same procedures as for single electrons (incl. background subtraction) But much harder cuts (plenty of statistics) Special emphasis on anti-deuteron removal γ-conversions, π0-Dalitz electrons removed via invariant mass Remaining 37% photonic electron background subtracted with v2max=17% Reaction plane resolution Yres ~ 0.7 Consistency check: PYTHIA + MEVSIM (v2 generator) + analysis chain  OK Analysis: v2 of Non-Photonic Electrons v2 = cos(2[Φ-Ψ]) / Ψres

  33. v2 of Non-Photonic Electrons • Indication of strong non-photonic electron v2 • consistent with v2(c) = v2(light quark) • smoothly extending from PHENIX results • Teany/Moor  D (2pT) = 1.5 (as = 1?)  expect substantial suppression RAA • Greco/Ko  Coalescence model (shown above) appears to work well Phenix : Min. Bias Star: 0-80% STAR: stat. errors only Phenix: nucl-ex/0404014 (QM2004) nucl-ex/0502009 (submitted to PRC) Star: J. Phys. G 190776 (Hot Quarks 2004) J. Phys. G 194867 (SQM 2004)

  34. Quarkonia in STAR • STAR: • Large acceptance |h|<1 • High tracking efficiency (90%) • J/Y:acceptance  efficiency (pTe > 1.2 GeV/c) ~ 10% • : Acceptance  efficiency (pTe > 3.5 GeV/c) ~ 14% • Without Trigger (min. bias running): • Min bias (100 Hz): 18 J/Y and 0.02  per hour running • Signal-to-Background Ratios • S/B > 1: 1 for  • S/B = 1:25 – 1:100 forJ/Y • Seff = S/(2(B/S)+1)  significance close to that of J/Y • STAR needs quarkonia triggers

  35. Quarkonia Trigger in STAR • J/Y  e+ e-: • L0-trigger: 2 EMC tower with E > 1.2 GeV (~60° apart) • L2-trigger (software): veto g, better E, 2.5 < Minv < 3.5 GeV/c2 • Efficiency currently too low in Au+Au (pp only)  need full ToF •  e+ e-: • L0-trigger: 1 EMC tower with E > 3.5 GeV • L2-trigger (software): Minv > 7 GeV/c2 • High Efficiency (80%) – works in Au+Au • Tests in Au+Au show it works • small background • counts = expectations • Need full EMC for that • 2004 ½ barrel EMC • 2005 ½ - ¾ barrel EMC trigger threshold No N+++N-- subtracted

  36. Summary and Outlook • Heavy Flavor Production in RHI is the next big topic that needs to be addressed • STAR has solid baseline measurements in pp and d+Au • D0 in d+Au from pT = 0 - 3 GeV/c • D* in d+Au mesons from pT = 1.5 – 6 GeV/c • Non-photonic single electrons in p+p and d+Au from 1.5 – 10 GeV/c • Measurements indicate a large scc in pp at RHIC • ds/dy|y=0 = 0.300.04(stat)0.09(sys) mb • NLO pQCD calculations under predict this value (~ a factor of 3-5) • Large scc appear to rule out expectation of J/ψ enhancement from some charm coalescence and statistical models • Preliminary results on v2 of non-photonic electrons indicate substantial elliptic flow of charm in Au+Au collisions at RHIC • consistent with v2c = v2light-q theory calculations • consistent (smoothly extending) with PHENIX results • try to extend to higher pT range (possibly b dominated) • First Results on J/Y and  soon

  37. STAR Collaboration 545 Collaborators from 51 Institutions in 12 countries Argonne National Laboratory Institute of High Energy Physics - Beijing University of Bern University of Birmingham Brookhaven National Laboratory California Institute of Technology University of California, Berkeley University of California - Davis University of California - Los Angeles Carnegie Mellon University Creighton University Nuclear Physics Inst., Academy of Sciences Laboratory of High Energy Physics - Dubna Particle Physics Laboratory - Dubna University of Frankfurt Institute of Physics. Bhubaneswar Indian Institute of Technology. Mumbai Indiana University Cyclotron Facility Institut de Recherches Subatomiques de Strasbourg University of Jammu Kent State University Institute of Modern Physics. Lanzhou Lawrence Berkeley National Laboratory Massachusetts Institute of Technology Max-Planck-Institut fuer Physics Michigan State University Moscow Engineering Physics Institute City College of New York NIKHEF Ohio State University Panjab University Pennsylvania State University Institute of High Energy Physics - Protvino Purdue University Pusan University University of Rajasthan Rice University Instituto de Fisica da Universidade de Sao Paulo University of Science and Technology of China - USTC Shanghai Institue of Applied Physics - SINAP SUBATECH Texas A&M University University of Texas - Austin Tsinghua University Valparaiso University Variable Energy Cyclotron Centre. Kolkata Warsaw University of Technology University of Washington Wayne State University Institute of Particle Physics Yale University University of Zagreb

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