Measurement of Open Charm Mesons in 200 GeV Heavy Ion Collisions at STAR

1. Measurement of Open Charm Mesons in 200 GeV Heavy Ion Collisions at STAR Stephen Baumgart Yale University

2. Outline • Charm Cross-Section in Cu+Cu • Motivation • Analysis Procedure • Results • Ds Measurement • Detector • Charge Asymmetry Question

3. Theory Motivation • Prediction of Charm Cross Section in p+p from QCD (NLO/FONLL) • Deviations from prediction in Cu+Cu, Au+Au collisions will show medium effects. Ref: M. Cacciari, P. Nason, R. Vogt, Phys. Rev. Lett. 95, 122001 (2005) • Charm production is a good probe of early state of medium • Charm produced during initial gluon fusion • Charm produced before thermalization. Ref: Kuznetsova, J. Rafelski Eur. Phys. J. C 51, 113-133(2007) Basic Gluon Fusion Diagram

4. Theoretical Uncertainties • Prediction 1 • use dpt slices, then integrate final result • treat charm as active flavor Charm Cross Section Predicted for 200 GeV Collisions: • Prediction 2 • calculate on full pt range in one step • treat charm as NOT an active flavor (heavy quark considered massive) Charm Cross Section Predicted for 200 GeV Collisions: • Ref: R. Vogt, arXiv:0709.2531v1 [hep-ph] The large error bars mean that experimental measurements are needed to help constrain theoretical predictions. Our STAR measurements will help resolve these discrepancies.

5. D0 to Kp Analysis Method in Cu+Cu MinBias Collisions Kaon Tracks Pion Tracks Unused Tracks D0 Mass Combinatorial Technique Rotational Background Subtraction or Event Mixing Background Subtraction py p Momentum and dE/dx cuts used px K 5 degree rotations 13 rotations

6. D0 + D0 in Minimum Bias Cu+Cu STAR Preliminary For Kp pairs: |y| < 1.0 pt < 4.0 GeV/c

7. ( D0 + D0)/2Spectra in Minimum Bias Cu+Cu |y| < 1.0 77% of area under curve is between 0.3 and 3.3 GeV/c! Fitting Function: *Systematic error evaluation for dN/dy in progress.

8. Conversion from dN/dy to Cross-Section number of binary collisions p+p inelastic cross section conversion to full rapidity (using PYTHIA simulation, ver. 6.152) ratio from e+e- collider data *Systematic error evaluation for dN/dy in progress.

9. Charm Cross-Section Comparison at 200 GeV • NLO Ref: R. Vogt, arXiv:0709.2531v1 [hep-ph] STAR: C. Adler, et al. Phys. Rev. Lett. 91 172302 (2003) S. Baumgart, arXiv:nucl-ex/0709.4223 Y. Zhang, arXiv:nucl-ex/0607011 *Systematic error evaluation for STAR Cu+Cu in progress. PHENIX: S. Adler, et al. Phys. Rev. Lett. 94 082301 (2005) S. Adler, et al. Phys. Rev. Lett. 97 252002 (2005)

10. Ds Motivation D/Ds ratio predicted by stat. hadronization model. Can be tested in STAR.

11. SVT Secondary Vertexing • Use SVT to find secondary vertices of Ds to fpdecay (ct = 149.9 mm). • Use mass cut on f to eliminate background.

12. The Ds Charge Asymmetry d+Au Ds+ Cu+Cu Ds+ d+Au Ds- Cu+Cu Ds-

13. Conclusions • The charm cross-section measured in Cu+Cu is consistent with other STAR charm cross-section measurements assuming binary scaling. • Current evidence suggests there may be many more Ds+ than Ds- ; however, more statistics are urgently needed. • New Au+Au and d+Au dataset are coming up!

14. D0 Reconstruction in Simulation (Backup) The D0 peak can be successfully recreated in simulation.

15. D0 from Kp in d+Au & Au+Au (Backup) D0 measured via Kp channel in Au+Au, d+Au. pt spectra obtained, yields measured. Counts D0 Peak Reconstructed from Kp in Au+Au, STAR Preliminary D0 Peak Reconstructed from Kp in d+Au, STAR Collaboration, J. Adams et al., Phys. Rev. Lett. 94, 062301 (2005).

16. Comparison to PHENIX Electrons (Backup) PHENIX and STAR: RAA for Non-photonic e± central Au+Au, √sNN=200 GeV Electron RAA matches PHENIX but not Yields! Red Circles and Blue Triangles = STAR Open Circles = PHENIX PHENIX: PRL 98 (2007) 172301 STAR: PRL 98 (2007) 192301 DVGL: Djordjevic, Phys. Lett. B 632 (2006) 81 BDMPS: Armesto, Phys. Lett. B 637 (2006) 362 Phys. Rev. Lett. 98, 192301 (2007)

17. Results from Non-Photonic Electrons (Backup) • The pt spectrum of open charm to electrons has been measured out to high pt. • Non-photonic electron measurements allow open charm spectra to be extended to high pt. B. I. Abelev et al, Phys. Rev. Lett. 98 (2007) 192301

18. Open Charm via Semi-Leptonic Decays (Backup) • Simulations show that high pt non-photonic electrons come almost exclusively from charm decays. • We use the STAR Electromagnetic Calorimeter (EMCAL) to detect these electrons. • Electrons from photonic conversions are cut from the sample. • Method is insensitve to details of the intervening material between interaction region and detector. black: e+e- pairs blue: comb. background red=photonic e±=black – blue Invariant Mass [GeV/c2]

19. Measuring Open Charm via Muons (Backup) • Muons are detected by the STAR Time-of-Flight (TOF) detector. • The muon measurement constrains the open charm yield at low pt. Muon Points Y. Zhang, arXiv:nucl-ex/0607011 Procedure Reference: H.D. Liu et. al., Phys. Lett.B 639, 441 (2006)

20. Heavy Ion Collisions (Backup) • Collisions in p+p, d+Au, Cu+Cu, Au+Au • Beam Energies of sq. root(SNN) = 20, 62, 130, 200 GeV • High Multiplicities relative to particle physics experiments

21. STAR Detector at RHIC (Backup) The Relativistic Heavy Ion Collider The Relativistic Heavy Ion Collider (RHIC) is located at Brookhaven, New York. RHIC uses p+p, d+A, and A+A beams. The STAR Detector 1) The Solenoidal Tracker at RHIC (STAR) is one of four major detectors. Beam Line • Three Ways to Study Open Charm: • Direct Hadronic Measurement (TPC) • Electron Measurement (EMCAL) • Muon Measurement (TOF) 2) 3)