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B c lifetime measurement using B c J/ y e X channel (Preblessing / cdfnote 7758)

B c lifetime measurement using B c J/ y e X channel (Preblessing / cdfnote 7758). Masato Aoki, Shinhong Kim University of Tsukuba Ilsung Cho, Intae Yu SungKyunKwan University Ting Miao FNAL. Introduction. We had measured the cross section of B c in J/ y +e X channel (note7518)

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B c lifetime measurement using B c J/ y e X channel (Preblessing / cdfnote 7758)

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  1. Bc lifetime measurement usingBcJ/y e X channel(Preblessing / cdfnote 7758) Masato Aoki, Shinhong Kim University of Tsukuba Ilsung Cho, Intae Yu SungKyunKwan University Ting Miao FNAL

  2. Introduction • We had measured the cross section of Bc in J/y+e X channel (note7518) • Electron ID using SoftElectronModule, dE/dx • Lxy>3sigma to kill prompt background • Background : • Fake electron : estimate fake rate, J/y+track as a control sample • Residual conversion : estimate conversion finding efficiency using B0J/y p0, p0gg or gee MC. Use J/y+tagged conversion • b-bbar : use Pythia MC, B+J/yK+ is used for the normalization • Fake J/y : J/y mass sideband subtraction • We release the lifetime cut and measure the Bc lifetime • New background from prompt events

  3. J/y+e selection cuts

  4. Summary of x-section measurement *Prompt BKG is killed by lifetime cut (Lxy>3sigma)

  5. Overview of lifetime measurement procedure • Same cuts as Bc x-section measurement (note7518) • Same technique for background fraction estimation • Background lifetime shapes from fitting background samples • Follow B+ lifetime measurement(CDF6266) for techniques • Single Gaussian as resolution function • Systematic error includes study of alternative resolution function and Punzi effect • K-factor estimation similar to that of BDln but with binning of M(J/y+e)

  6. Summary after releasing lifetime cut Excess contains prompt BKG and Bc signal

  7. Background fraction • Background fraction (the denominator includes prompt bkg and Bc signal) • fake e : 0.141 +/- 0.022 • res. conv : 0.086 +/- 0.041 • bbbar : 0.080 +/- 0.022 • fake J/y : 0.209 +/- 0.012 • Statistical and systematic errors are included • Constrain the fractions for the final fitting using Gaussian

  8. 0 0 0 0 1 1 1 1 2 2 2 2 K-factor

  9. Additional cuts for the lifetime analysis • Check sLxy distribution • B+J/yK+ • J/y+electron • Use sLxy<70mm

  10. Fitter check using B+J/yK+ • Simply check our fitter using B+J/yK+ • Result • ct=504.1  9.3mm • Agree with blessed result from CDF

  11. Overview of background shape determination • Fake electron : • J/y+track with electron fake rates • Fake J/y : • Sideband in J/y+track candidates • Residual conversion : • J/y+tagged conv. electron with conversion finding efficiency • b-bbar : • Pythia MC but with change of GS/FE/FC for systematic error • Prompt : • Assume to be resolution function

  12. Fake electron • PDF for fake electron BKG e : fake rate N : normalization factor can be expected from J/y mass distribution * Use same error scaling factor for both real J/y and fake J/y here

  13. fake J/y parameterization • PDF for fake J/y

  14. Fit results of fake electron & fake J/y table  next page

  15. Fit results of fake electron & fake J/y l : mm

  16. Issue on fake J/y shape • J/y+track, conversion sample have fake J/y component as well as J/y+electron • Looking at fake J/y+track, conversion, electron events, we found their shapes are similar see next page • Use common fake J/y shape • Use J/y+track sample for every fake J/y shapes • Limited stat. for conversion, electron samples

  17. J/ysideband event comparison J/y+track • similar shapes J/y+electron J/y+conv.-e

  18. Residual conversion • PDF for residual conversion BKG Constrain fake J/y and scale factor

  19. Fit result of conversion BKG l : mm Constrained using J/y+track sample

  20. b-bbar background • PDF for b-bbar BKG • Background events passing selection cut from each production process • Gluon splitting : 70% • Flavor excitation : 25% • Flavor creation : 5% (scaling factor is not constrained) Syst. study : GS and FE

  21. Fit result of b-bbar BKG l : mm

  22. Prompt background • It is difficult to estimate the size of prompt background from either MC or data  Float prompt BKG fraction for the final fitting • We use resolution function as prompt background shape (Gaussian)

  23. Likelihood definition for the signal fitting • PDF for signal • Likelihood

  24. Signal fitting ct(Bc)= 142.6 +22.2/-19.9 mm

  25. signal fitting (cont’d)

  26. Systematic uncertainties • K-factor • M(Bc), pT(Bc),lifetime(Bc),decay channel,… • Background shapes • fake J/y shapes, w/o efficiency weighting,… • Resolution function (follow CDF6266) • Choice to treat Punzi effect as systematic error for now • Double Gaussians, Gaussian+symmetric exponential • Silicon alignment  borrow the result of B lifetime analysis using J/y+X exclusive mode

  27. Systematics from K-factor • M(Bc)  6.291, 6.251 GeV  142.4, 142.6 mm  Dct :  0.2 mm • t(Bc)  0.4, 0.7 ps  142.3, 142.4 mm  Dct :  0.3 mm • HbJ/yX spectrum  141.3 mm  Dct :  1.3 mm • Trigger simulation  142.8 mm  Dct :  0.2 mm • Inclusive BcJ/yXen channel (K factor  next page)  142.1 mm  Dct :  0.5 mm

  28. K-factor for inclusive Bc decays

  29. Systematics from background shapes • Fake J/y : Use J/y+e sideband • 137.5 mm  Dct : -5.1 mm • Res. conv. : Use J/y+conv sideband • 145.1 mm  Dct : +2.5 mm • b-bbar : No error scaling in MC fitting  140.8 mm  Dct : - 1.8 mm

  30. fake rate / finding efficiency weighting Fake e : 141.2 mm  Dct : -1.4 mm Conv. : 141.7 mm  Dct : -0.9 mm J/y+conv.-e J/y+track

  31. b-bbar : 100% FE, 100% GS l : mm • 100% FE  152.4 mm : Dct = +9.8 mm • 100% GS  140.6 mm : Dct = -2.0 mm

  32. Different resolution functions • Single Gaussian • Double Gaussians • Gaussian + symmetric exponential •  Convolute

  33. J/y+track fit result for Gaussian+Symmetric Exp. ct(Bc)=136.5 mm  Dct : -6.1 mm

  34. J/y+track fit result for Double Gaussians ct(Bc)=136.2 mm  Dct : -6.4 mm

  35. ct error distributions for Punzi effect ct(Bc)=138.0 mm  Dct : -4.6mm

  36. Systematics from ct resolution • Resolution function  Dct : -6.4 mm • Punzi effect (sct of fake J/y, fake e, conv, others)  Dct : -4.6mm • Silicon alignment effect from note7409  Dct : 1.0 mm

  37. Summary of systematic errors K factor  1.5 mm BKG shapes +10.1 / -6.0 mm Resolution +1.0 / -7.9 mm Total:+10.3/-10.0 mm

  38. Summary • We measured the Bc lifetime using J/y+electron • ct(Bc)=142.6 +22.2/-19.9(stat.) 10.3(syst.) mm or • t(Bc)=0.475 +0.074/-0.066(stat.) 0.034(syst.) ps • Details are described in note7758 • Theoretical prediction • 0.55 0.15 ps • Run1 CDF • 0.46 +0.18/-0.16 0.03 ps • Run2 D0 • 0.448 +0.123/-0.096 0.121 ps

  39. Backup

  40. fake J/y with 2 negative exponentials • Why fake J/y fit quality is so bad? • complicated shape at ct<0 of fake J/y event makes bad fit quality • try to add one more negative exponential •  see next page • result of Bc fitting: ct(Bc) = 142.1 mm • the effect of the negative side is –0.5 mm

  41. fake J/y with different parameterization w/ one negative exponential w/ two negative exponentials

  42. b-bbar : FE only fixing s=1.25

  43. For the lifetime measurement • Same cuts as Bc x-section measurement (note7518) • Mass window : M(J/y+e)=4 ~ 6GeV/c2 • Background • fake electron : use J/y+track • fake J/y : use fake J/y+track • residual conversion : use J/y+tagged conv. • b-bbar : Pythia MC • prompt : resolution function (Gaussian) • Use common fake J/y shape for J/y+track, J/y+conv., J/y+electron samples • Constrain background shapes using Gaussian • K-factor Divide by 4 mass bins (4-4.5, 4.5-5, 5-5.5, 5.5-6 GeV/c2)

  44. Gaus+Gaus && Punzi effect • Resolution function is fixed using B+ events • RF parameters from B+J/yK+ fitting • s=1.271 +0.018/-0.017 • fs2=0.10 +0.016/-0.014 • s2=3.07 +0.18/-0.17 • J/y+e fit result with new RF && Punzi term • ct(Bc) = 131.4 +21.5/-19.2 mm Dct(Bc) = -11.2 mm

  45. Gaus+Sym. Exp && Punzi effect • Resolution function is fixed using B+ events • RF parameters from B+J/yK+ fitting • s=1.284 +0.015/-0.015 • fexp=0.21 +0.03/-0.03 • sexp=1.70 +0.13/-0.11 • J/y+e fit result with new RF && Punzi term • ct(Bc) = 134.4 +21.8/-19.4 mm Dct(Bc) = -8.2 mm

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