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Open Charm from RHIC --- recent results from STAR

Xin Dong University of Science & Technology of China Lawrence Berkeley National Laboratory. Open Charm from RHIC --- recent results from STAR. for the STAR Collaboration. Outline Introduction & Motivation Direct charm reconstruction Indirect electron measurements Discussion

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Open Charm from RHIC --- recent results from STAR

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  1. Xin Dong University of Science & Technology of China Lawrence Berkeley National Laboratory Open Charm from RHIC--- recent results from STAR for the STAR Collaboration • Outline • Introduction & Motivation • Direct charm reconstruction • Indirect electron measurements • Discussion • Conclusions & outlook

  2. D mesons Large Q value needed (>≈3GeV) pQCD should work better! , Y’, c π0 measurements are consistent with NLO pQCD calculation! Charm should be better!! PHENIX, PRL 91, 241803(2003) STAR, PRL 92, 171801(2004) Heavy flavor in pQCD

  3. (p)QCD Test Total cross section measurement --- not depend on the fragmentation models  A powerful test of QCD calculations ! Charm spectrum measurement --- fragmentation test for theory predictions.

  4. Charm quark mostly produced from the initial fusion of partons (mostly gluons) Q2 Z. Lin & M. Gyulassy, PRC 51 (1995) 2177 time Heavy flavors – a unique probe to QGP J/y, D W f X L, K* p, K D, p d

  5. Y. Dokshitzer &D. Kharzeev PLB 519(2001)199 M. Djordevic & M. Gyulassy QM04, nucl-th/0404006 J. Adams et. al, PRL 91(2003)072304 Heavy quark energy loss ● Heavy Quark has less dE/dx due to suppression of small angle gluon radiation “Dead Cone” ΔE of heavy quarks --- Probe the medium property !

  6. Statistical model: Large ccbar yield in one heavy ion collision  recombination production J/ψ  possible J/ψ enhancement Statistical model A. Andronic et. al. PLB 571,36(2003) J/ψ production: suppression/enhancement? • J/ψ suppression scenario in QGP ! --- Debye screening Total charm yield from pQCD calculations!

  7. Single electrons  Open charm v2 At pT > 2.5 GeV/c: 1) D-meson spectrum is ‘hard’, yields of pion will be small, measure D-decayed electron to infer the open charm v2 2) D-meson flow  indication of light flavor thermal equilibrium. X. Dong et. al, PLB597, 328(2004).

  8. Low-energy fixed target – direct D measurement CDF directy D measurement -- high pT CDF, PRL 91, 241804 (2003) Fermilab E769, PRL 77, 2388 (1996) ISR 52-63GeV – inconsistency, S.P.K. Tavernier Rep. Prog. Phys. 50, 1439 (1987) UA2: 630 GeV p+pbar (two electron data points), O. Botner et al. PLB 236 (1990) 488 Previous Experiments

  9. Measurements in heavy ion collisions PHENIX Au+Au@130GeV Phys. Rev. Lett. 88, 192303 (2002) • Nbin scaling for open charm spectrum • Total cross section consistent with NLO pQCD calculation

  10. STAR detector Barrel EM Cal (BEMC) Silicon Vertex Tracker (SVT)Silicon Strip Detector (SSD) FTPCEndcap EM CalFPD TOFp, TOFr Year 2001+ Magnet Coils Central Trigger Barrel (CTB) ZCal Time Projection Chamber (TPC) Year 2000

  11. ( Br. 3.83%) D0 direct reconstruction STAR PRL, in print Event mixing technique First Direct Open Charm Reconstruction at RHIC

  12. D mesons measured at STAR STAR Preliminary

  13. Open charm spectrum STAR Preliminary • D*/D0 ratio is consistent with other experiments and models • Power-law describes the spectrum well up to ~11GeV/c

  14. Indirect measurement D→e+X STAR PRL, in print TOF Hadron identification: STAR Collaboration, nucl-ex/0309012 electrons Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!! A new detector --- a prototype of TOF base on MRPC technology

  15. 1. With TOF and dEdx, electrons can be identified well from ~0.3GeV/c up to ~3GeV/c! 2. Select electrons (e-) using dE/dx only (2-4GeV) Inclusive electrons Hadron contamination was corrected for ~ 5-30% pT 2-4 GeV/c STAR Preliminary

  16. γ conversion π0, η Dalitz decays Kaon decays ρωΦ vector meson decays heavy quark semi-leptonic decay others Single Electrons Spectra background signal γ conversion and π0Dalitz decays are the dominant sources at low pt region. TPC Measurements of electron background • Background Topology: • TOFr tagged e+/e- • Large TPC acceptance • High efficiency of reconstructing • electron pair For the γconversion and π0 Dalitz decay, background spectra are obtained from data using kinematical selection of the pairs in TPC

  17. Background subtraction Invariant Mass Square STAR Preliminary • Data: background spectrakinematical selection of the  conversion and 0 Dalitz decay pairs in TPC • MC: conversion and 0 Dalitz decay reconstruction efficiency~60% • c) MC: relative contributions of • different sources: • determined from PYTHIA/HIJING + detector simulations Signal Rejected  conversion and 0 Dalitz decay reconstruction efficiency : ~60% at pT>1.0 GeV/c STAR Preliminary

  18. Background contribution STAR PRL, in print An increasing excess found at higher pT region, pT > 1.0 GeV/c, →expected to be contribution of semileptonic decay from heavy flavor hadrons

  19. Combining fit Combined fit for D0 and electrons STAR PRL, in print PYTHIA: MSEL = 1, CTEQ5M1 1) Good agreement between D0 and electrons spectra 2) d+Au and p+p do not show significant nuclear effect

  20. p+p and d+Au electron spectra show approximately binary scaling 1<pT<4GeV/c Charm yields Assumption for the combining fit: 1. D0 spectrum follows the power law function 2. only normalization scale between different D meson pT spectrum 3. All the background subtracted electrons are from D decay

  21. Mid-rapidity → Full rapidity 4.7 ± 0.7 Charm production cross-section STAR PRL, in print • NLO pQCD calculations under predict the total charm production cross section at RHIC • Scales (muR or muF) may be energy dependent • Power law description from SPS->RHIC • n = 1.9 +- 0.2 • (0.3 for charged multiplicity)

  22. Consistency check STAR Preliminary STAR Preliminary Directly reconstructed D mesons Electrons from D decay D and electron spectra are consistent!

  23. MRST HO Peterson’s function ε=0.06 c quark =4,3,2,1 (GeV)^2 Charm quark hadronization at RHIC bare c-quark spectrum, normalized to measured dn/dy After broadening and fragmentation R. Vogt, hep-ph/0203151 STAR Preliminary A. Tai QM04 1) Higher order processes needed 2) Charm hadronization through fragmentation + recombination?

  24. Non-photonic electron v2 Greco, Ko, Rapp, Phys. Lett. B595, 202(04) Systematic errors are important! STAR: 0-80% (F.Laue SQM04) PHENIX: Minimum bias statistical error only corrected for e± from  decay M. Kaneta et al, J.Phys. G30, S1217(04)

  25. Conclusions Both direct open charm reconstruction and indirect charm semi-leptonic decay electrons are measured at STAR in d+Au collisions. They provide consistent results. Total charm cross section from this measurement is higher than NLO pQCD calculations. Preliminary D meson spectrum appears to imply a unusual hard fragmentation function for charm quarks. Study open charm v2 and J/ yields to address thermalization issues at RHIC. The run-IV data will just do that.

  26. Upgrade at STAR STAR MRPC - TOF STAR MicroVertex Tracker Full open charm measurements Full resonance measurements with both hadron and lepton decays

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