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B c lifetime measurement using J/ y +e final state

B c lifetime measurement using J/ y +e final state. Masato Aoki University of Tsukuba. Introduction. The B c meson is the ground state involving two heavy quarks(charm and bottom) It was first seen by the CDF in Run-I 110pb -1 data using J/ y +lepton channel

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B c lifetime measurement using J/ y +e final state

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  1. Bc lifetime measurement using J/y+e final state Masato Aoki University of Tsukuba CDF-Japan meeting

  2. Introduction • The Bc meson is the ground state involving two heavy quarks(charm and bottom) • It was first seen by the CDF in Run-I 110pb-1 data using J/y+lepton channel • We also confirmed the Bc signal in J/y+electron channel with 360pb-1 CDF Run-II data (5.9s) CDF-Japan meeting

  3. Backgrounds • Fake J/y • Fake electron • Residual conversion • b-bbar • Prompt CDF-Japan meeting

  4. Event selection • Mostly same as cross-section measurement except lifetime cut • pT m:1.5GeV for CMU (2.0GeV for CMX), e:2GeV, J/y:3GeV, J/y+e:5GeV • Df(J/y-e)<90degree • eID • Likelihood-based(e~70%), dE/dx(e~90%) • Mass window • 4 < M(J/y+e) < 6GeV • Lifetime resolution • sLxy < 70 mm CDF-Japan meeting

  5. J/y+e candidates and partial background estimation Excess contains prompt BKG and Bc signal CDF-Japan meeting

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

  7. Background samples • Fake J/y • J/y+trk sideband (similar shape as J/y+e,J/y+conv sideband) • Fake electron • J/y+trk weighted by fake rate • Residual conversion • J/y+tagged conv. weighted by finding efficiency • b-bbar • Pythia MC (generic QCD : msel=1) • Prompt • Resolution function (single Gaussian) CDF-Japan meeting

  8. Procedure • Background lifetime shapes from fitting background samples • Single Gaussian as resolution function • Use same error scaling factor for both real J/y and fake J/y here • 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) CDF-Japan meeting

  9. K-factor CDF-Japan meeting

  10. Fake J/y shapes J/y+electron J/y+conv.-e CDF-Japan meeting

  11. Fake electron CDF-Japan meeting

  12. Residual conversion Constrained using J/y+track sample CDF-Japan meeting

  13. b-bbar CDF-Japan meeting

  14. 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) CDF-Japan meeting

  15. Likelihood definition for the signal fitting • PDF for signal • Likelihood CDF-Japan meeting

  16. J/y+e data fit • The changes from input values (from fitting bkg sample) and returned values of final fitting are well within errors ct = 142.1 +21.9/-19.7 mm CDF-Japan meeting

  17. J/y+e lifetime distribution CDF-Japan meeting

  18. Systematic uncertainty CDF-Japan meeting

  19. J/y+e mass distribution J/y+trk with Lxy<-3s normalization : lifetime fit result CDF-Japan meeting

  20. Summary • Bc lifetime measured with J/y+e channel • 0.474 +0.074/-0.066 0.033 ps • References • Run-I CDF (J/y+e & J/y+m) • 0.46 +0.18/-0.16  0.03 ps • Run-II D0 (J/y+m) • 0.448 +0.123/-0.096  0.121 ps • Theoretical prediction • 0.55  0.15 ps CDF-Japan meeting

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