1 / 38

A First Look at Open Charm Production in d+Au and p+p at s = 200 GeV with the STAR Detector

A First Look at Open Charm Production in d+Au and p+p at s = 200 GeV with the STAR Detector. Thomas Ullrich, BNL/Yale Stony Brook, Nov 12, 2003. Why measure open charm in A+A, p+p, p+A? What do we know about charm production at s = 200 GeV? D mesons in d+Au collisions

symona
Download Presentation

A First Look at Open Charm Production in d+Au and p+p at s = 200 GeV with the STAR Detector

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A First Look at Open Charm Production in d+Au and p+p at s = 200 GeV with the STAR Detector Thomas Ullrich, BNL/Yale Stony Brook, Nov 12, 2003 • Why measure open charm in A+A, p+p, p+A? • What do we know about charm production at s = 200 GeV? • D mesons in d+Au collisions • The single electron spectra in p+p and d+Au • Suppression of charm in Au+Au? • Conclusions & Outlook

  2. Charming Particles General: charm mesons & baryons are heavy (mc ~ 1.3 GeV/c2) relative long lifetime (ct >> RAu)

  3. Production of Charm ? • Charm produced in early stage, mostly from • initial gluon fusion • g g cc • Sensitive to early conditions: • initial gluon density • nuclear effects • medium effects Are charm mesons suppressed ?

  4. Suppression in Au+Au: Baryons versus Mesons STAR: nucl-ex/0306007 PHENIX: PRL 91, 172301 • Suppression of inclusive hadron yield at high pTin Au+Au • central Au+Au collisions: factor ~4-5 suppression • pT>5 GeV/c: suppression ~ independent of pT and species (meson vs. baryon) • pQCD describes data only when energy loss is included

  5. Suppression of Charm ? Dokshitzer, Kharzeev, PLB 519 (2001) 199 • Propagation of charm quarks in QCD matter •  Energy loss through gluon radiation • dead cone effect  large enhancement of D/ ratio at moderate high pT (5-10 GeV/c) Heavy Quark has less dE/dxdue to suppression of small angle gluon radiation Charm quark found to loose only ~10% of their energy during propagation at RHIC energy

  6. Does Charm Flow? In A+A collisions,interactions among constituentsand density distribution lead to: pressure gradient  collective flow  driven by Equation of State (EOS) • Charm quark elliptic flow • helps to distinguish between • no final state (PYTHIA) • thermal equilibrium • Need v2(pT) • insights in dynamics of charm in matter (Lin, Molnar nucl-th/0304045) RHIC SPS KSH, hep-ph/0006129

  7. Thermal Charm ? • No thermal creation of c • mc ~ 1.3 GeV/c2 >> T • c quarks interact with lighter quarks  thermal recombination ? • Ds+ yield sensitive • J/Y: suppression vs recombination ? **No suppression * A.Andronic, P.Braun-Munzinger, K.Redlich, J.Stachel, nucl-th/030306.

  8. Hidden (Quarkonium) and Open Charm? • NA38/NA50:measurement of J/Y, Y suppression at CERN/SPS: • Suppression with respect to • continuum (Drell-Yan) • Low statistics • Nbin/Npart from Glauber • Model dependent • Fluctuations! • RHIC: • Continuum dominated byopen charm • also: Statistical models: relative chemical equilibrium between open charm and J/Y? Open charm production provides a good reference and may be the only mean to understand charmonium suppression (same gluon conditions in the initial stage)

  9. What do we know about charm production in p+p? • Different PDF sets or quark masses lead to different energy dependences • All the curves are normalized at low energies • the ‘predictions’ for higher energies have a certain spread : •  changing PDF sets : range 400–800 mb at RHIC energies changing c quark mass by 15% : range 300–700 mb RHIC CTEQ6M compiled by H. Woeri and C. Lourenco (SQM2003)

  10. What do we know about charm production in A+A? PHENIX Au+Au@130GeV Phys. Rev. Lett. 88, 192303 (2002)

  11. Many Reasons to Measure Open Charm at RHIC • There are lot’s of ideas on the market: • Open charm suppression (dead cone effect) ? • Partonic flow ? • Thermalization ? • Need to understand open charm to evaluate J/Y production and suppression • But we know little so far about charm production at RHIC • A+A (except single-e from PHENIX)? • p+A ? • p+p (current data does not allow reliable predictions) • Before we address A+A we need to understand p+p and p+A

  12. STAR measuring charm in hadronic channels: D0  K(B.R. 3.8%) and K p r (B.R. 6.2%) D  K p(B.R. 9.1%) D*±D0π (B.R. 68%) Lc p K p (B.R. 5%) TPC (PID only at low pT) SVT (vertex not well known) ToF (acceptance too small) STAR measuring charm in leptonic channels: c  e X TPC (tracking  pT ) ToF (PID < 3 GeV/c) EMC (PID > 1 GeV/c) The STAR Experiment during Run-III (d+Au and p+p)

  13. D0 in STAR: Analysis Methods K p • Event-Mixing Technique • Identify charged Kaon and Pion tracks • through energy loss in TPC • Produce oppositely charged K- pair • invariant mass spectrum in same event • Obtain background spectrum through • mixed event • Subtract background and get D0 spectrum • d+Au: 15.7 M events D0 K- Pair Invariant Mass

  14. D0 Invariant Mass Spectrum D0+D0 to increase statistics 0 < pT < 3 GeV/c, |y| < 1.0 Gaussian function + linear Residual background • 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

  15. D0 - Transverse Mass Spectra Color bands stand for different pT range Exponential Fit From spectra and fit to spectra: dN/dy and slope (T) 8

  16. Systematic Uncertainty Studies (I) Change Normalization Factor R R=0.1400 Yield Change: -16% R=0.1423 R=0.1440 Yield Change: +12% 9

  17. Systematic Uncertainty Studies (II) • Fit with open mass and width parameters: • dN/dy change: -0.003 • T change: -19 MeV 10

  18. Systematic Uncertainty Studies (III) • Fit with Gaussian + Polynomial O(2) • dN/dy change: +0.001 • T change: -4 MeV 11

  19. Systematic Uncertainty Studies (IV) • Different Cut Set • dN/dy change: -0.005 • T change: -20 MeV 13

  20. D0: Total Systematic Uncertainty dN/dy = 0.033 ± 0.005 ± 0.008 T = 303 ± 48 ± 28 MeV 14

  21. D* Mesons in d+Au Collisions D*±D0π (B.R. 68%) Decay Kinematics (Pythia) “Golden channel” for open charm study Standard method: M(D*±) – M(D0)=145.421 MeV Width~1 MeV Difficulty: the low efficiency of the soft pion reconstruction STAR full field: tracks curl up for pT < 100 MeV/c

  22. D* Mesons in d+Au Collisions D0  K-p+p0 (B.R. 13.1%) D* D0 D0 from D* decays Masses and Widths OK: m(D*)-m(D0) =0.1467±0.00016 GeV/c2 m(D*)-m(D0)(PDG)=0.1454 GeV/c2 m(D*)-m(D0)(MC)=0.1451 GeV/c2 width=0.43±0.14 MeV width(MC)=0.67 MeV D0K+π+π0

  23. D Mesons in d+Au Collisions • D± mass=1.864±0.0052 GeV/c2 • D± mass(PDG)=1.869 GeV/c2 • D± mass(MC)=1.868±0.002 GeV/c2 • width = 13.83±3.7 MeV • width (MC)=14.9±1.6 MeV • D±Kππ (B.R. 9.1%) • 3-body decay  more background • high-pT reach D±

  24. D* and D Spectra in d+Au Min. Bias Collisions Assuming: yield of D* = directly-produced D± Using: D*±  D±p0 (31%)  scale D± points by 0.765 • Preliminary results: • dN/dy((D*+ + D*-)/2) = 0.0151±0.0018(stat)±0.0040 (sys) • <pT> = 1.250±0.041(stat)±0.150(sys) GeV/c • D*/D0 = 0.46±0.10(stat)±0.15(sys) • Comparisons: • D*/D0 = 0.49 (Pythia) • D*/D0 = 0.54±0.06 (CDF) • D*/D0 = 0.38±0.13 (HERA) STAR preliminary

  25. D0 - Mean Transverse Momentum D0: pT = 1.073 ± 0.170 (stat.) ± 0.100 (sys.) GeV/c D*: pT = 1.250±0.041(stat) ± 0.150(sys) GeV/c ISR mT scaling Bourquin-Gaillard Relatively large mean pT in p+p Pythia calculations and d+Au measurements  D0 is produced from gluon fusion D* 16

  26. PYTHIA & D Spectra in d+Au Min. Bias Collisions PYTHIA: used parameter set from PHENIX tuned to match charm cross-sections in hadronic (incl. p induced) collisions kT = 1.5 GeV/c mc = 1.25 GeV/c2 K-factor = 3.5 PDF = CTEQ5L PARP(67) = 1 σ(cc) = 653μb Saturation model in d+Au from Kharzeev and Kuchin, hep-ph/0310358 The measured D spectrum can not be reproduced by PYTHIA with the above parameters.

  27. Preliminary Estimate of Total Charm Cross Section Using D0 only since it covers low-pT best Total cross section for pp  c c • = 0.033 / 54% / 7.5 * 42 mb * 4 = 1385 ± 216 ± 353 b where: 0.033: (D0+D0)/2 dN/dy • 54%: charm to D0 fraction • from e+e- collisions at 10GeV • 7.5: Nbinary in d+Au minbias collisions • 42 mb: p+p inelastic cross section • 4: Integral over rapidity From H. Worhi, CIPANP 2003

  28. d+Au: More charm, more channels soon … Anti particle included |y| < 0.9 Anti particle included |y| < 0.5 We do not understand this peak yet: mass shifted, yield too high ! D0 mass is shifted by 14 MeV. Cut Dependence? Caused by Rho? D0 decays outside of the fire ball! Hard to check the systematics due to low statistics.

  29. Single Electron Spectra in d+Au: PID with ToF • New technology: MRPC, first developed by CERN ALICE • p/K separation up to 1.6 GeV/c • p/K separation up to 3 GeV/c • Thus cover wider range of(p,K,p) pT But only 10 modules (12) installed (p/30, –0.5<eta<0.) In d+Au: used as trigger (enhancement factor ~10)

  30. Electron PID with MRPC TOF/TPC TPC dE/dx only |1/β-1| < 0.03 electrons With TOF PID cut, electron band can be separated from others readily!

  31. Sources for Electron γ conversion π0, η Dalitz decays Kaon decays ρωΦ vector meson decays heavy quark semi-leptonic decay others Single Electrons Spectra γ conversion and π0Dalitz decays are the dominant sources at low pT region Model known sources as precisely as possible and compare with data (including 0, scalar and vector mesons contribution)

  32. Background Subtraction Opening Angle 1. Select an primary electron/positron (tag it) dAuTOF data Invariant Mass Square Signal 2. Select another opposite sign track anywhere in TPC Rejected “Measure” background

  33. Background Subtraction ► Using kinematical cuts and compare the data and simulation to get the estimated main sources of γ conversion and p0 Dalitz decay ► Using decay generators to get the single electrons spectra according to the assumed (pT, y) distributions for h, r, w, f An increasing excess found at higher pT region  expected to be contribution of semi- leptonic decay from heavy quarks (dominantly by charm quark)

  34. Single Electron Spectra from d+Au and p+p Cross-check: Generate electrons from measured D mesons in d+Au  consistent • Charm cross-section: • STAR’s D0 from d+Au → 1385 216b • single electron from d+Au → 1516311b (Statistical error only here)

  35. Suppression of Charm ? Electron and (D meson) spectrum in d+Au collisions higher than the electron spectrum from Au+Au and some of the PYTHIA results with particular parameter settings. STAR Preliminary Increasing deviation → Heavy flavor energy loss(?) in heavy ion collisions Au+Au data from R. Averbeck’s talk at INT/RHIC Winter Workshop

  36. Conclusion • First measurement of D0, D, and D* in d+Au collisions at RHIC • pT coverage: • 0 < pT < 3 GeV/c for D0 • 1.3 <pT< 6.0 GeV/c for D* • 6.7 <pT< 11 GeV/c for D • pTis high (1-1.2 GeV/c) – expected when gluon fusion is dominant production mechanism • ppc c total cross section derived from D0 meson spectra • Can exclude various Parton Distribution Function • Measurement of single-electron spectra in p+p and d+Au • pT coverage: pT < 3 GeV/c • measure large fraction of background • spectra and cross-section consistent with D meson spectra • not described by PYTHIA • Comparison between single-electron spectra in p+p and d+Au with Au+Au implies very interesting physics….

  37. Outlook • Single-electron spectra from EMC analysis in d+Au • will extend to range were b starts dominating • Looking forward to Run-IV • ¾ Barrel EMC and full Endcap EMC (-1 < h < 2) • loooong Au+Au run will allow • D meson study • and thus RAB of D mesons • Single-electron spectra from 0 to ~10 GeV/c (ToF and EMC) • and thus RCP of charmed mesons • Future: • full barrel ToF (2p, |h|<1) will improve electron PID

  38. D* D*-D0 Au+Au: A first glimps of D* in half field data … STAR not even preliminary D0 from D* Coming Au+Au run at s=200 GeV will allow us to study open charm production with better accuracy

More Related