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Shin-Shan Yu ( 余欣珊 ) Fermi National Accelerator Laboratory

Measurement of the Ratio B ( L b  L c mu )/ B ( L b  L c p ) && Search for Anomalous Production of Diphoton + e/ m at CDF. Shin-Shan Yu ( 余欣珊 ) Fermi National Accelerator Laboratory Academia Sinica HEP Seminar, January, 2007. DATA SAMPLE FOR THE ANALYSES. Diphoton + e/mu

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Shin-Shan Yu ( 余欣珊 ) Fermi National Accelerator Laboratory

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  1. Measurement of the Ratio B(LbLcmu)/B(LbLcp)&& Search for Anomalous Production ofDiphoton + e/m at CDF Shin-Shan Yu (余欣珊) Fermi National Accelerator Laboratory Academia Sinica HEP Seminar, January, 2007

  2. DATA SAMPLE FOR THE ANALYSES Diphoton + e/mu Mar 2006 shutdown Lambdab relative BR Sep 2003 shutdown Shin-Shan Yu

  3. Measurement of the Ratio B(LbLcmu)/B(LbLcp)

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

  5. BIG PICTURE : WHY Lb BARYON? • Heavy Quark Effective Theory (HQET) simplifies the extraction of CKM elements • Assuming mb >> LQCD • Corrections expressed in the power • of 1/mb and as(mb) • Spin-independent interaction between light quarks and b quark • Spin of light degrees of freedom = 0, the corrections are simpler than those of b-mesons. u d b q ud Shin-Shan Yu

  6. HOWB(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

  7. 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

  8. FORMULA REMINDER Shin-Shan Yu

  9. ANALYSIS REQUIREMENTS Shin-Shan Yu

  10. SIGNAL SAMPLELbLcXLc p+ K-p+ Hadronic Signal Inclusive b hadron -> Xmn decays reconstructed as Lcm Background shapes come from MC c2/NDF=36.6/42 Prob=70.7% Inclusive Semileptonic Signal Combinatorial and b-> other c hadron semileptonic decays Shin-Shan Yu

  11. FORMULA REMINDER Shin-Shan Yu

  12. MC AND DATA COMPARISON BEFORE AFTER PT(Lb)[GeV/c] PT(Lb)[GeV/c] • 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) Shin-Shan Yu

  13. FORMULA REMINDER Shin-Shan Yu

  14. SOURCES OF SEMILEPTONIC BACKGROUND • Feed-down/Feed-in from single b-hadron decays • Single b-hadron -> …. -> Lcm + additional particles e.g: • Hadrons mis-identified as muons • Real Lambdac and real muon from the decay of two heavy-flavor hadrons Shin-Shan Yu

  15. FEED-DOWN/IN FROM SINGLE B-HADRON • Reduced by the M(Lcm) cut • Normalize the amount of background to the measured hadronic signal • BR from PDG or estimated from theory and CDF preliminary measurements • Reconstruct as many backgrounds as possible • PDG BR(Lb -> LcmX)=9.2%constrain BR of the other backgrounds • ~10% contribution Shin-Shan Yu

  16. MIS-IDENTIFIED MUONS m? • 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 • ~3% contribution Shin-Shan Yu

  17. Lc m FROM TWO HEAVY-FLAVOR HADRONS p+ Lc+ Lc+ p+ • 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 hard gluon splitting • ~0.2% contribution • Assign 100% uncertainties Shin-Shan Yu

  18. SEMILEPTONIC SAMPLE FRACTION Shin-Shan Yu

  19. CONSISTENCY CHECK Shin-Shan Yu

  20. UNCERTAINTY SUMMARY Feed-in/down background and hadronic signal branching fractions MC modeling of production, decay, 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 Shin-Shan Yu

  23. Unexpected and additionalphysics results

  24. FIRST OBSERVATION of NEW Lb DECAYS 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 Shin-Shan Yu

  25. CROSS-SECTION RATIO AND B(Lb  Lc p) • Make use of previous CDF measurements • Lb PT spectrum using fully reconstructed decay was not available for CDF I • Correct the CDF I cross-section ratio using measured PT spectrum • Acceptance correction • Different PT thresholds affect the ratio 10 GeV/c vs. 6 GeV/c ??? Consistent with the prediction 0.45% (Phys. Lett. B586, 337) Shin-Shan Yu

  26. B0 AND Lb PT SPECTRA FROM DATA Shin-Shan Yu

  27. WHAT DO WE KNOW ABOUT Lb NOW? (4.1  2.0) x 10-3 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

  28. Siganature-based Search for Anomalous Production of Diphoton + e/m at CDF

  29. MOTIVATION Phys. Rev. D59, 092002 (1999) by Toback, et al • CDF Run I “ee+MET” event: 86 pb-1 • Dominant SM:WW 810-7 events • Total:~10-6events • Personal • Use calorimeters • Learn high-pt physics Shin-Shan Yu

  30. RUN II PHOTON ANALYSES • Diphoton + X • X = e, m,t, g, met, b-jet, jet • Expand photon analysis to a more systematic search • Do not optimize cuts based on any model • Only compare kinematic distributions and number of events • Look for excess above background prediction • Not a blind analysis • Lepton + photon + X • X = met, e, m, g, met + b jet • Other model-dependent photon analyses • RS graviton to diphoton search • more … • +X signatures • SUSY: +MET+X • b`b`bb • l*l*ll, q*q*qq • New dynamics Shin-Shan Yu

  31. A RUN II gge EVENT Is it from SM? Fakes from jets or electrons ? Or new physics? Shin-Shan Yu

  32. ANALYSIS OVERVIEW Includes a wire chamber at showermax • Require two central photons and lepton objects • photons || < 1.0 • muons || < 1.0 • electrons || < 2.0 • Specific detector requirements for each lepton type • Data sample ~ 1.1 fb-1 collected with diphoton trigger • 2 EM clusters with Et > 12 GeV • isolation, E_had/E_em, shower profile requirements • Compare prediction with observation by applying several levels of loose and tight photon requirements Shin-Shan Yu

  33. ANALYSIS REQUIREMENTS Shin-Shan Yu

  34. DIPHOTON + e/mFROM SM AND FAKES • W gg, Z gg: Madgraph MC, weighted with data/MC ID scale factor, luminostiry, trigger efficiency, K factor to correct LO to NLO cross-section • Fake leptons + real photons: apply lepton fake rates to the events with 2 photon candidate + fakeable object, then scale with the true photon fraction obtained from MC and data (showermax and preshower radiator) • True photon fraction ~ 30% for photon Et > 13 GeV • Leptons + fake photons from jets: apply jet faking photon rate to the events with lepton candidate + photon candidate + a central jet • W g, Z g + jet • g + 2 jets where 1 jet fake lepton • W or Z + 2 jets where both jets fake photons • Z + jet where electron fakes a photon • Leptons + fake photons from electrons: apply electron faking photon rate to the events with lepton candidate + photon candidate + an electron • Z g where the electron comes from decay of Z • Z + jet where the jet fakes a photon Shin-Shan Yu

  35. DOMINANT BACKGROUND Z Z Z l • electron channel • eeg from Zg where one electron fakes the photon • muon channel • Z gg Shin-Shan Yu

  36. REJECT FAKE PHOTONS USING SILICON TRK • Measure the fake rate • Compare Z peak from ee and eg • Get Et dependence from MC • Normalize to data • Silicon-track rejections reduce the fake rate by a factor of 3-4 • Electron can fake a photon due to track-loss, FSR or BREM • Background from BREM can be reduced by removing photons matched to silicon tracks • tracks seeded by event vertex and a cluster in the EM calorimeter Silicon track rejection applied 0.36% at 45 GeV Shin-Shan Yu

  37. Result The event which survives silicon-track rejection. M(egg)=129.5 GeV/c2 M(eg1)= 93.0 GeV/c2 M(eg2)= 88.3 GeV/c2 = Sum Et of observed objects and missing Et Shin-Shan Yu

  38. CONCLUSION • We have measured the Lb relative branching fraction using 173 pb-1 • We have made the first observation of 4 Lb semileptonic decays • We have the first evidence that the Lb pt spectrum is softer than that of the B0 meson. • Although Bs mixing is already observed, there’re still interesting B physics to do at the Tevatron. With current available data, we could make a more precise measurements of b-baryon properties or search for unobserved b-baryons. • We have searched for anomalous production of diphoton + e/mu events in 1 fb-1 of data. No excess is observed. • Removing photons matched to silicon tracks reduce the electron faking photon rate by a factor of 4 • Keep looking … Shin-Shan Yu

  39. Back Up Slides

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

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

  42. Physics Background Shin-Shan Yu

  43. 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

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

  45. Lb Polarization Shin-Shan Yu

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