1. Recent Charm Measurements through Hadronic Decay Channels with STAR at RHIC in 200 GeV Cu+Cu Collisions Stephen Baumgart for the STAR Collaboration, Yale University 1 August 18, 2008

2. Outline 1) Motivation 2) Analysis Procedure 3) D 0 Analysis 4) Charm Cross-Section 5) D s Analysis 6) Outlook August 18, 20082

3. Charm Production Prediction of Charm Cross-Section in p+p from perturbative Quantum Chromodynamics (pQCD) (NLO/FONLL) Ref: M. Cacciari, P. Nason, R. Vogt, Phys. Rev. Lett. 95, 122001 (2005) Charm produced during initial gluon fusion. – Therefore, we expect the cross-section to scale with the number of binary collisions – Charm produced before thermalization. – Charm is therefore a good probe of the quark-gluon plasma medium.

4. Charm Cross-Section from Theory Charm Cross Section Predicted for 200 GeV Collisions: Ref: R. Vogt, arXiv:0709.2531v1 [hep-ph] Method 1: use dp t slices, then integrate final result treat charm as active flavor FONLL Calculation Charm Cross Section Predicted for 200 GeV Collisions: Method 2: calculate on full p t range in one step treat charm as NOT an active flavor (heavy quark considered massive) NLO Calculation 4August 18, 2008

5. Measuring Heavy Flavor Secondary vertices are located by using the Silicon Vertex Tracker (SVT). These can be used for open charm measurements. 5 Charm or beauty is created early in the evolution of the Quark Gluon Plasma, generally from gluon fusion. Full hadronic reconstruction done by using the Time Projection Chamber (TPC) The STAR Detector August 18, 2008

6. D 0 to K  Analysis Method in Cu+Cu Minimum Bias Collisions Combinatorial Technique Rotational Background Subtraction or Event Mixing Background Subtraction Kaon Tracks Pion Tracks Unused Tracks Momentum and dE/dx cuts used pypy pxpx   5 degree rotations 13 rotations D 0 Mass 6August 18, 2008

7. D 0 + D 0 in Minimum Bias Cu+Cu STAR Preliminary For K  pairs: |y| < 1.0 p t < 4.0 GeV/c 7August 18, 2008

8. Double Counting Systematic Error Double Counting may cause yields to be exaggerated Simulations suggest that the effect is negligible when using certain cut sets. Results from simulation can be used to determine degree of systematic error in real data. Check will be done using embedded D 0 s. August 18, 20088

9. D 0 Reconstruction in Simulation The D 0 peak can be successfully recreated in simulation. 9August 18, 2008 Embedding Simulation

10. ( D 0 + D 0 )/2 Spectra in Minimum Bias Cu+Cu Fitting Function: |y| < 1.0 10August 18, 2008

11. Conversion from dN/dy to Cross-Section p+p inelastic cross section conversion to full rapidity (using PYTHIA simulation, ver. 6.152) ratio from e + e - collider data number of binary collisions *Systematic error evaluation for dN/dy in progress. 11August 18, 2008 0 - 60% Centrality

12. Charm Cross-Section Comparison at 200 GeV *Systematic error evaluation for STAR Cu+Cu in progress. NLO Ref: R. Vogt, arXiv:0709.2531v1 [hep-ph] PHENIX: S. Adler, et al. Phys. Rev. Lett. 94 082301 (2005) S. Adler, et al. Phys. Rev. Lett. 97 252002 (2006) STAR: J. Adams et al. Phys. Rev. Lett 94, 062301 (2005) S. Baumgart, arXiv:nucl-ex/0709.4223 Y. Zhang, arXiv:nucl-ex/0805.0364 12August 18, 2008

13. Charm Cross-Section Conclusions August 18, 200813 STAR has measured the charm cross-section to be near the pQCD upper limit. STAR results from multiple systems are consistent with binary scaling. Global results are generally higher than the NLO prediction.

14. Secondary Vertex Finding for D s mesons using the SVT Finding the secondary vertex using the Silicon Vertex Tracker (SVT) allows one to use geometric cuts to identify particles with decay lengths  from ~100  m to 10s of centimeters. August 18, 200814  (negligible decay length)  K+K+ K-K- D s + (c  = 149.9  m) Primary Vertex Secondary Vertex To Detectors To find D s mesons, I take only decays with decay lengths between 100 and 400  m.

15. Looking for D s   through use of SVT Secondary Vertexing:  Resonance August 18, 200815 These are  s with displaced vertices. STAR Preliminary

16. D s from using the SVT in Cu+Cu 16 Weak ~3 sigma D s + peak found from reconstruction of D s      K + K -   No D s - found. August 18, 2008 STAR Preliminary

17. D s Charge Asymmetry? Cu+Cu D s + Cu+Cu D s - d+Au D s - d+Au D s + August 18, 200817 STAR Preliminary

18. Summary/Outlook Charm cross-section in Cu+Cu measured to be near upper pQCD limit and consistent with binary scaling Systematic error evaluation and propagation will be completed for D 0 in Cu+Cu Hadronic D 0 results can be combined and compared with non-photonic electron results in Cu+Cu (Anders Knospe) D s charge asymmetry in Cu+Cu and d+Au collisions, measurement in new Run 8 d+Au data should illuminate issue August 18, 200818

19. Calibration of TPC dE/dx Measurements (Backup) The TPC dE/dx energy loss can be calibration by identifying resonance decays. Since the decay daughters are known, they can be used for calibration. August 18, 200819 In Progress!

20. Using the Time Projection Chamber (Backup) August 18, 200820 The STAR Time Projection Chamber (TPC) measures both rigidity and energy loss (dE/dx). From these, the masses of particles traversing the detector can be found. Kaon Tracks Pion Tracks Unused Tracks

21. Systematic Error Evaluation (Peak Fitting) (Backup) 21 Different methods and possible cuts are checked in order to evaluate the systematic errors. Different binnings checked (5,15,25 MeV/bin) Different fit ranges (200 MeV range for start and finish of Gaussian fit. Peaks are STABLE under different fit ranges + binnings! But subtraction method introduces systematic error. August 18, 2008 Yields Gaussian Widths Gaussian Centroids STAR Preliminary