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Update on Partially Reconstructed Mode Combinatorial Background

Explore mass and lifetime distributions, analyze WS and RS in upper sideband, and evaluate mass dependencies. Conclusions emphasize agreement and areas for improvement in understanding combinatorial backgrounds.

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Update on Partially Reconstructed Mode Combinatorial Background

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  1. Update on Combinatorial Background for Partially Reconstructed Modes Amanda Deisher B Mixing and Lifetimes May 30, 2006

  2. Outline • Mass Distributions • Mass shape of WS in partially reconstructed mass regions • Possible physics backgrounds in WS • Lifetime Distributions • RS and WS in upper sideband • Mass dependence of RS • Mass dependence of WS • Conclusions

  3. Ingredients • Data Sample: B0D- [K+  - -]  + xbhd0h(0i) Wrong Sign (WS): D- [K+  - -] - • Metric for Agreement: • Binned 2 test • Unbinned Kolmogorov test • Lc veto: Remove if 2.26 < m(Lc ) < 2.31 GeV/c2 • D* veto: Remove if m(Kpp) - m(Kp) < 0.18 GeV/c2 • Lifetime: Definition Jeff Miles has been using The definition I’ve been using for this analysis

  4. Mass Distributions Analysis cuts only DR < 1.5 p PT > 1.2 Lxy(B)/sLxy(B) > 11. Lxy(BD) > -0.0300 +Lc veto +D* veto • |d0B| < 0.0110 • c2xy(B) < 15.0 • c2xy(D) < 15.0 • candPT > 5.5

  5. Mass Shape of WS in PR region • Does the WS distribution in the partially reconstructed region agree with the RS combinatorial background extrapolation? • Procedure: • Fit exponential + flat background to RS upper sideband • Extend curve to PR region & compare • Results depend on sideband definition: • Varied fit range (multiple curves) • (5.6,6.38)  (5.8,6.38) • Note: shape of combinatorial will be constrained with full mass fit (see CCKMP…) RSWS

  6. WS Single B Physics Background 25000 • Look at B+D+X andB0D+X Monte Carlo RS:reco’d as D+  - 35 WS:reco’d as D+  + Physics background in WS small and below region of interest

  7. WS and RS Agreement in Upper Sideband 5.4 < m < 5.7 GeV/c2 RS , WS ct (cm) 6.0 < m < 6.3 GeV/c2 RS , WS 5.7 < m < 6.0 GeV/c2 RS , WS ct (cm) ct (cm)

  8. WS and RS Agreement in Upper Sideband Mass structure in (5.5,5.6) region not understood. Try looking at agreement without this contribution. • WS and RS agree very well in the upper sideband, independent of ct definition

  9. Mass Dependence of RS ct Normalized to unit area ct (cm)

  10. Mass Dependence of RS ct • Removing region (5.5,5.6) with unexplained mass structure • What if we just start above 5.6? • Using the visible mass  some mass dependence, significantly less than when using PDG mass

  11. Mass Dependence of WS ct Normalized to unit area ct (cm)

  12. Mass Dependence of WS ct • Removing region (5.5,5.6) with unexplained mass structure • What if we just start above 5.6? • Hmm, the first and last mass bins don’t agree at all

  13. Mass Dependence of WS ct • Looking WS ct in the signal region (5.1,5.4) • Looking WS ct in the partially reconstructed region (4.8,5.1) • Definite mass dependence. Still need to work on optimizing cuts in this region.

  14. Conclusions • Full mass fit necessary to evaluate level of agreement between WS and current combinatorial background model • Initial studies show little WS single B physics background in PR or signal region • RS and WS ct distributions agree in the upper sideband and show same mass dependence • Using visible mass in ct calculation greatly reduces mass dependence • WS seems to track mass dependence of RS in the region where we can test it. While we will use the wrong sign as a proxy, we need to look at reducing the systematics by optimizing S/B in the PR region.

  15. To-Do List • Perform full mass fit with templates for PR and then compare the shape of the extrapolated RS combinatorial bkgd and the WS combinatorial bkgd in the PR region • Evaluate systematic uncertainty on the B lifetime introduced by the uncertainties in the mass and lifetime dependence of the combinatorial bkgd • Re-optimize cuts to minimize this uncertainty

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