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

SVT Review, 07/07/06Sarah LaPointe2 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

SVT Review, 07/07/06Sarah LaPointe3 Detecting Heavy Mesons Hadronic Channels Branching Ratio D 0  K -  + 3.8% D +/-  K   9.2% Semileptonic Channels D 0  e + + anything6.9% D +/-  e +/- + anything 17.2% B 0  e + + anything 10.9% Techniques used to measure open charm? Event Mixing Single Electrons Direct Hadron Reconstruction

SVT Review, 07/07/06Sarah LaPointe4 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.

SVT Review, 07/07/06Sarah LaPointe5 Assumptions In simulations the SVT and SSD are 100% active. The SVT has a (realistic) position resolution of 80  m (fast simulator) plus TPC slow simulator and GEANT. Vertex smearing of 150 micron. We only attempted reconstruction of D0 to K -  + 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%.

SVT Review, 07/07/06Sarah LaPointe6 Results from pure D0 events without cuts 350 K single D0 events (PYTHIA). 16,500 trackable D0 (rapidity & primary vertex distr.)

SVT Review, 07/07/06Sarah LaPointe7 Results from pure D0 events with cuts 706 reconstructed D0, reconstruction efficiency: 4.3%

SVT Review, 07/07/06Sarah LaPointe8 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  m, < 7 mm DCA V0 to PV: < 300  m DCA pos daughter to PV: > 100  m, < 400  m DCA neg daughter to PV: > 100  m, < 400  m DCA neg to pos: < 500  m dE/dx: nsig(  ) 0.7 GeV PVz cut: cm Rapidity cut: no

SVT Review, 07/07/06Sarah LaPointe9 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

SVT Review, 07/07/06Sarah LaPointe10 Results: 200 GeV CuCu p06id (no cuts) 300,000 events: Many zero SVT hit candidates (cut parameter) Plots with more stats will follow

SVT Review, 07/07/06Sarah LaPointe11 Results: 200 GeV CuCu p06id (cuts) No signal in 300,000 events, background suppression factor = 11,000 Plots with more stats will follow

SVT Review, 07/07/06Sarah LaPointe12 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

SVT Review, 07/07/06Sarah LaPointe13 Comparison p06ib (TPC only) to p06id No signal in 300,000 events, significantly wider DCA distributions p06ib p06id

SVT Review, 07/07/06Sarah LaPointe14 Reference for 200 GeV AuAu: Haibin’s mixing analysis with TPC only Significance = S/sqrt(S+2B) = 4 Year-4 data P05ia production, minbias trigger 0-80% centrality, |VertexZ|<30 cm~13.3M |NSigmaPion|<3| |NSigmaKaon|<2 |NSigmaKaon| 0.7 GeV/c) p>0.3 GeV/c, pT>0.2 GeV/c nFitPnts>15, |eta|<1, gDCA<1.5 cm |PairRapidity|<1

SVT Review, 07/07/06Sarah LaPointe15 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 N bin 2 = 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.

SVT Review, 07/07/06Sarah LaPointe16 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 Reconstruction efficiency: 4.3% = 43,000 D0 reconstructed Signal per event: 43,000/60 Million = 0.007/event Background: scale CuCu background by N bin 2 (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: –Significance: S/sqrt(S+2B) = 14 (compared to 4.5 in Haibin’s analysis

SVT Review, 07/07/06Sarah LaPointe17 Summary Based on our analysis STAR should be able to topologically reconstruct D0 in the K  channel using the SVT and SSD in: –5 Million minbias CuCu events –60 Million minbias AuAu events