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First Measurement of the Ratio B ( L b  L c mu )/ B ( L b  L c p ) at CDF

First Measurement of the Ratio B ( L b  L c mu )/ B ( L b  L c p ) at CDF. Shin-Shan Yu University of Pennsylvania SLAC Experimental Seminar, August 11th, 2005 http://www-cdf.fnal.gov/physics/new/bottom/050407.blessed-lbbr/. Outline. L b. udb. Why L b CDF Detector, Trigger

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First Measurement of the Ratio B ( L b  L c mu )/ B ( L b  L c p ) at CDF

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  1. First Measurement of the Ratio B(LbLcmu)/B(LbLcp)at CDF Shin-Shan Yu University of Pennsylvania SLAC Experimental Seminar,August 11th, 2005 http://www-cdf.fnal.gov/physics/new/bottom/050407.blessed-lbbr/

  2. Outline Lb udb • Why Lb • CDF Detector, Trigger • Lb Relative Branching Fractions Shin-Shan Yu

  3. Big Picture : Why Lb Baryon? u d b Shin-Shan Yu

  4. Experiment B(LbLcmu)/B(LbLcp) ? and • Relative BR is the yield ratio corrected for the efficiency, e.g: • Four charged tracks in the final state • Data come from the same trigger, most systematics cancel. • Control samples: similar decays in the B meson system But since we can not reconstruct neutrinos, several backgrounds can fake our semileptonic signals in the data …. Shin-Shan Yu

  5. CDF Detector & Trigger • Silicon Tracker • || < 2 • svertex ~ 30 mm • Central Outer Tracker (COT) • 96 layers drift chamber, up to ||~1 • sPT/PT~ 0.15% PT • Central Muon Chamber • 4 layers drift chamber outside the calorimeter • || < 0.6 • Two Displaced-track Trigger • pT > 2 GeV/c, 120 m ≤ d0≤ 1 mm, • Lxy> 200 m,S pT > 5.5 GeV/c • 150 M events analyzed for this measurement Shin-Shan Yu

  6. Signal SampleLbLcXLc p+ K-p+ Hadronic Signal Background shapes come from MC c2/NDF=36.6/42 Prob=70.7% Inclusive Semileptonic Signal Shin-Shan Yu

  7. Control SampleB0 DX, D+ K-p+ p+ Inclusive Semileptonic Signal Hadronic Signal Background shapes come from MC Shin-Shan Yu

  8. Control SampleB0 D*X, D*+ D0p+, D0 K-p+ Inclusive Semileptonic Signal Hadronic Signal Background shapes come from MC Shin-Shan Yu

  9. MC and Data Comparison: Before • We used MC to obtain relative efficiencies of signals and backgrounds. • Compare MC and background subtracted signal distribution in the data. • Tune our MC if MC and data disagree, e.g: PT(Lb), M(Lcm) PT(Lb)[GeV/c] M(Lcm)[GeV/c2] Shin-Shan Yu

  10. MC and Data Comparison : After Shin-Shan Yu

  11. Where Are the Semileptonic Backgrounds from? • Physics Background • b-hadron -> …. -> Lcm + additional particles e.g: • Reduced by the M(Lcm) cut • Normalize the amount to the measured hadronic signal • BRs come from PDG, theoretical estimate and preliminary measurements • ~10% contribution Shin-Shan Yu

  12. First Observation of Lb Semileptonic Background CDF Run II Preliminary 360 pb-1 Sc++ Lc(2625) Lc(2593) Sc0 Sc++,+,0 CDF Run II Preliminary 360 pb-1 CDF Run II Preliminary 360 pb-1 Lc(2625) Lc(2593) • Estimated BR of the reconstructed background based on the first observation • PDG BR(Lb -> LcmX)=9.2% Shin-Shan Yu

  13. How to ObtainB(Lb  Lc p)? Consistent with the prediction 0.45% (Phys. Lett. B586, 337) • Make use of previous CDF measurements • Lb MC PT spectrum using fully reconstructed decay was not available for CDF I • Correct the CDF I flambdab/fd using measured PT spectrum • Acceptance correction • Different PT thresholds affect the ratio 10 GeV/c vs. 6 GeV/c Shin-Shan Yu

  14. How to ObtainB(Lb  Lc p)? Shin-Shan Yu

  15. Where Are the Semileptonic Backgrounds from? m? • Muon Fakes • p, K, p fake muons • ct and muon d0 cuts suppress prompt fakes • Our fakes mostly come from b decays • Weight “Lc+TRKfailm” events with the Pfake • p, K, p fractions from the inclusive B MC • ~5% contribution Shin-Shan Yu

  16. Where Are the Semileptonic Backgrounds from? • QCD Pair Production: • charm and m from different b- or charmed hadrons • Suppressed due to the ct and PT(m) cuts • Rely on Pythia MC • Most sensitive to gluon splitting • ~0.2% contribution p+ Lc+ Lc+ p+ Shin-Shan Yu

  17. Inclusive Semileptonic Sample Composition Shin-Shan Yu

  18. Consistency Check Shin-Shan Yu

  19. Dominant Systematics • Physics background and hadronic signal branching fractions • Measured: from PDG • Estimated:multiply the BR by 2 or 0 • Mass fitting model • Vary the constant parameters in the fit • Several background shapes come from inclusive MC • vary BR of the dominant decays • MC modeling of acceptance and efficiency • pT spectrum • affect the efficiency and B (LbLcp) • Lb semileptonic decay model • size of the independent MC for reweighting the phase space distribution • uncertainty on the predicted form factors Shin-Shan Yu

  20. Uncertainty Summary Physics background and hadronic signal branching fractions MC modeling of efficiency and acceptance Shin-Shan Yu

  21. Control Sample Result Consistent with the 2004 world average 7.81.0 at the 1s level Consistent with the 2004 world average 19.71.7 at the 0.7s level New world average ratio 8.3  0.9 New world average ratio 19.1  1.4 Shin-Shan Yu

  22. Signal Sample Result • Experimental Uncertainties • dominated by: • Data sample size • B (LbLcp) • CDF Run I fbaryon/fd • B(Lc->pKp) Shin-Shan Yu

  23. What Do We Know aboutLb Now? (4.1  2.0) x 10-3 Lc l u (5.0  1.9) % DELPHI (Phys. Lett. B585, 63) Lc l u/ Lc p 20.0  3.7 Lc(2593) +l u seen Lc(2625)+l u seen Sc++p-l u seen Sc0p+l u seen Shin-Shan Yu

  24. Back Up Slides

  25. Heavy Quark Effective Theory (HQET) simplifies the calculation of b-hadron BR • Assuming mb >> LQCD • Corrections expressed in the power • of 1/mb and as(mb) • Spin of light degrees of freedom = 0, the corrections are simpler than those of b-mesons. q ud Shin-Shan Yu

  26. Physics Background Shin-Shan Yu

  27. MC Tuning Flat phase space Form factor weighted Shin-Shan Yu

  28. Lb Polarization Shin-Shan Yu

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