Christopher Morrison 2006 Pope Fellowship Michael Sokoloff Brian Meadows University of Cincinnati

1. Measurement of D0gK-p+ absolute branching fraction using partially reconstructed D*+gD0p+ Christopher Morrison 2006 Pope Fellowship Michael Sokoloff Brian Meadows University of Cincinnati

2. Introduction u p+ d W c s K- • The D0 meson. • Quark Content: charm, anti-up • Mass: 1.8646 (GeV/c2) • Lifetime: 410 X 10-15 (sec) • Motivation • The D0gK-p+decay is used frequently in normalizing branching fraction measurements. • Most recent measurement has 2% precision. • 3.91 ± 0.08 ± 0.09% (CLEO 2005) • 2006 PDG Average 3.80 ± 0.07% • Thanks to Babar’s large data sample, we can push the precision down. D0 u u Christopher Morrison

3. Babar Detector Electro-Magnetic Calorimeter (EMC) Instrumented Flux Return (IFR) 1.5 T Magnet e+ e- Ring Imaging Cerenkov Detector (DIRC) Drift Chamber (DCH) Silicon Vertex Tracker (SVT) Christopher Morrison

4. Overview of Analysis p+“Slow Pion” pT K- pL D*+ D0 p+ - cc e+ e- Tag • Our analysis looks for D*+gD0p+ in a sample of fully reconstructed charm events. We then find the fraction of D0’s from D*+ that decay to K-p+ to calculate the absolute branching fraction. Christopher Morrison

5. Tag Sample • Three reasons for using tag. • Defines an event axis. • pT and pL • Defines a right and a wrong sign. • p+(slow) charge agrees/disagrees with Tag. • Gives a clean sample of events to work with. • 5 tag modes will be used in all. • Plots shown are from Rolf Andreassen’s D+gK-p+p+ sample. • Other modes are • D*+gD0p+, D0gK-p+ • D*+gD0p+, D0gK-p+p0 • D*+gD0p+, D0gK-p-p+p+ • D0gK-p+ Christopher Morrison

6. D*+ Partial Reconstruction • After tagging look at recoil side of the event. • Look for charged tracks and calculate pT2. Should peak at low values for slow pion tracks from D*+. • Right sign in blue • Wrong sign in red • Lots of background • We will use the wrong sign as a model for the background. Christopher Morrison

7. Background Subtraction • Fit the ratio of right sign slow pions to wrong sign. • Use fit to scale the wrong sign. • Subtract scaled wrong sign from right sign. • The signal in the lower right is the number of D*+gD0p+ in our sample and thus the number of D0’s. Christopher Morrison

8. D0 • For each slow pion, we then reconstruct K-p+ and plot the invariant mass. • We observe a peak at the D0 mass. • Require: mass(D*+) – mass(K-p+) =mass(p+) • The number of D0’s seen here over total D0’s (slow pions) gives the branching fraction. Christopher Morrison

9. What’s next? • Calculate efficiency for K-p+ reconstruction. • Look at simulated signal events (Monte Carlo). • D0 Reflections • Our D0 signal is somewhat polluted by other decays that are mis-reconstructed. • D0gK-K+ • D0gp-p+ • D0gK-p+p0. • Systematic Errors • Error in slow pion background subtraction • Error in tracking efficiency. Christopher Morrison

10. Conclusions • No measurement yet, but our result is looking promising. • We should be able to drive the measurement down to a 1% statistical uncertainty with the four remaining tagging modes. Christopher Morrison

11. Acknowledgements • Michael Sokoloff • SLAC • Brian Meadows • Giampiero Mancinelli • Kalanand Mishra • Rolf Andreassen • Kevin Flood • Adam Edwards and Stephanie Majewski • Mike Woods • Richard Gass • Andrei Kogan • Everyone at SLAC and UC • You, the Audience Christopher Morrison

12. References [1] CLEO Collaboration Q. He et al. PRL 95, 121801 (2005) [2] W.-M. Yao et al. (Particle Data Group), J. Phys G 33, 1 (2006) [3] Babar Collaboration B. Aubert et al., Nucl. Instr. And Methods A479, 1 (2002) Christopher Morrison

13. Questions? Christopher Morrison