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Topological D-meson Reconstruction with STAR Using the Silicon Vertex Tracker (SVT)

Topological D-meson Reconstruction with STAR Using the Silicon Vertex Tracker (SVT). Sarah LaPointe Wayne State University SVT review, BNL, July 7 th /8 th , 2006. Overview. Method Strategy Results from simulation of pure D0 events Results from simulation of D0 embedded in HIJING

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Topological D-meson Reconstruction with STAR Using the Silicon Vertex Tracker (SVT)

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  1. Topological D-meson Reconstruction with STAR Using the Silicon Vertex Tracker (SVT) Sarah LaPointe Wayne State University SVT review, BNL, July 7th/8th, 2006

  2. Overview • Method • Strategy • Results from simulation of pure D0 events • Results from simulation of D0 embedded in HIJING • Results from p06id & p06ib 200 GeV CuCu productions • Estimates for AuAu minbias running • Summary Sarah LaPointe

  3. Detecting Heavy Mesons Hadronic Channels Branching Ratio • D0 K-+ 3.8% • D+/-  K  9.2% Semileptonic Channels • D0 e+ + anything 6.9% • D+/-  e+/- + anything 17.2% • B0  e+ + anything 10.9% • Techniques used to measure open charm? • Event Mixing • Single Electrons • Direct Hadron Reconstruction Sarah LaPointe

  4. Strategy • Determine the reconstruction efficiency by optimizing a topological cut set in pure D0 events • Test the cut set on D0’s embedded in HIJING • Determine the background suppression factor achievable using such cuts in a realistic event sample (200 GeV CuCu production) • Project the significance of the method to measure D-mesons in 200 GeV AuAu. Sarah LaPointe

  5. Assumptions • In simulations the SVT and SSD are 100% active. The SVT has a (realistic) position resolution of 80 mm (fast simulator) plus TPC slow simulator and GEANT. Vertex smearing of 150 micron. • We only attempted reconstruction of D0 to K-p+ • In real data the detector inefficiency has to be taken into account. The hardware efficiency during the CuCu run varied between 65-85%. For the runs used here the efficiency was closer to 80%. Sarah LaPointe

  6. Results from pure D0 events without cuts • 350 K single D0 events (PYTHIA). 16,500 trackable D0 (rapidity & primary vertex distr.) Sarah LaPointe

  7. Results from pure D0 events with cuts • 706 reconstructed D0, reconstruction efficiency: 4.3% Sarah LaPointe

  8. Final cuts from cut optimization • Number of TPC points on track: 25 • Number of SVT points on track: > 1 • Number of SSD points on track: > 0 • Decay length: > 300 mm, < 7 mm • DCA V0 to PV: < 300 mm • DCA pos daughter to PV: > 100 mm, < 400 mm • DCA neg daughter to PV: > 100 mm, < 400 mm • DCA neg to pos: < 500 mm • dE/dx: nsig(p)<3, nsig(K)<2, nsig(K)<1 if p>0.7 GeV • PVz cut: +- 30 cm • Rapidity cut: no Sarah LaPointe

  9. Results from D0 in HIJING events • Based on 220 K HIJING minbias 200 GeV CuCu events. One D per event but not all trackable (f=20) • Background almost realistic: 7/event (should be 10/event with no cuts) • Signal is a factor 2.5 too high (factor 20 more because of non-trackable events, factor 50 less because of branching ratio, acceptance and primary tracking efficiency) • Ideal detector: we see a signal !! • S/B = 1/14 (realistically 1/35), significance = S/sqrt(S+2B) = 1.7 (in 220 K events) before cuts after cuts Sarah LaPointe

  10. Results: 200 GeV CuCu p06id (no cuts) • 300,000 events: Many zero SVT hit candidates (cut parameter) Sarah LaPointe Plots with more stats will follow

  11. Results: 200 GeV CuCu p06id (cuts) • No signal in 300,000 events, background suppression factor = 11,000 Sarah LaPointe Plots with more stats will follow

  12. Caveats and projections for 200 GeV CuCu production • Detector is not 100% alive (somewhere between 65-85%) • 2 hit requirement in SVT more stringent than in simulation • Inefficiency in global tracker • With a 100% efficient the significance in a 3 Million event CuCu analysis is about 6. • Assuming a factor 2 reduction in the signal due to detector and tracking in efficiencies gives me a significance of S/sqrt(S+2B) = 3 for 3 Million event and S/sqrt(S+2B) = 4 for 5 Million events. Signal in 5 Million events = 4,500 counts • Conclusion: 5 Million minbias CuCu events yield a good signal Sarah LaPointe

  13. Comparison p06ib (TPC only) to p06id • No signal in 300,000 events, significantly wider DCA distributions p06ib p06id Sarah LaPointe

  14. Reference for 200 GeV AuAu: Haibin’s mixing analysis with TPC only Year-4 data P05ia production, minbias trigger 0-80% centrality, |VertexZ|<30 cm~13.3M |NSigmaPion|<3| |NSigmaKaon|<2 |NSigmaKaon|<1 (p>0.7 GeV/c) p>0.3 GeV/c, pT>0.2 GeV/c nFitPnts>15, |eta|<1, gDCA<1.5 cm |PairRapidity|<1　 • Significance = S/sqrt(S+2B) = 4 Sarah LaPointe

  15. The Background consistency check (CuCu to AuAu) • background in Haibin’s study (no cuts, but some dE/dx, rapidity and fitpoints restrictions): 220/event in AuAu • scaled down to CuCu via Nbin2 = 11/event • my CuCu background from p06id with no cuts: 44/event • with Haibin’s cuts: 10/event • with topological cuts: 0.004/event • Conclusion: background is consistent. Sarah LaPointe

  16. Projection for D-mesons in 200 GeV AuAu • raw signal (based on Haibin’s analysis) using 3.8% branching ratio, 50% acceptance plus primary tracking efficiency: 1 Million D in 60 Million minbias AuAu events • 60 Million is based on a 11 week run in 2007. • Reconstruction efficiency: 4.3% = 43,000 D0 reconstructed • Signal per event: 43,000/60 Million = 0.007/event • Background: scale CuCu background by Nbin2 (f=20). • CuCu bkgd, no cuts: 44/event, with cuts: 0.004/event (f=10,000) • AuAu bkgd: 0.004*20=0.08/event • S/B in 60 Million AuAu events: 0.0875 • Significance: S/sqrt(S+2B) = 14 (compared to 4.5 in Haibin’s analysis Sarah LaPointe

  17. Summary • Based on our analysis STAR should be able to topologically reconstruct D0 in the Kp channel using the SVT and SSD in: • 5 Million minbias CuCu events • 60 Million minbias AuAu events Sarah LaPointe

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