October 18, 2005 CDF-Japan meeting 1

Bc lifetime measurement using J/+e final state

Masato Aoki

University of Tsukuba

October 18, 2005 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/+lepton channel

• We also confirmed the Bc signal in J/+electron channel with 360pb-1 CDF Run-II data (5.9)

October 18, 2005 CDF-Japan meeting 3

Backgrounds

• Fake J/• Fake electron

• Residual conversion

• b-bbar

• Prompt

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Event selection• Mostly same as cross-section measurement except

lifetime cut– pT

:1.5GeV for CMU (2.0GeV for CMX), e:2GeV, J/3GeV, J/+e:5GeV

– (J/-e)<90degree– eID

• Likelihood-based(~70%), dE/dx(~90%)

• Mass window– 4 < M(J/+e) < 6GeV

• Lifetime resolution– Lxy < 70 m

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J/+e candidates and partial background estimation

Excess contains prompt BKG and Bc signal

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Background fraction• Background fraction (the denominator includes

prompt bkg and Bc signal) – fake J/ : 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

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Background samples• Fake J/

– J/+trk sideband (similar shape as J/+e,J/+conv sideband)

• Fake electron– J/+trk weighted by fake rate

• Residual conversion– J/+tagged conv. weighted by finding efficiency

• b-bbar– Pythia MC (generic QCD : msel=1)

• Prompt– Resolution function (single Gaussian)

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Procedure• Background lifetime shapes from fitting background samples

• Single Gaussian as resolution function

• Use same error scaling factor for both real J/ and fake J/ here

• Systematic error includes study of alternative resolution function and Punzi effect

• K-factor estimation similar to that of BDl but with binning of M(J/+e)

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K-factor

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Fake J/ shapes

J/+electron

J/+conv.-e

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Fake electron

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Residual conversion

Constrained using J/+track sample

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b-bbar

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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)

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Likelihood definition for the signal fitting

• PDF for signal

• Likelihood

)]s|G(ct*)cτ

*Kct(ct*)Exp([

cτ

KH(K)dK Fsig

))G(f)G(f)G(fG(fL bbJ/ fakeconv. res.e fakeconstrain bkg

error) mean,|G(paramL BKGconstrainparameter

sigpromptJ/ fakebbconv.e fakelifetime )Ff-f-f-f-f-[(1L

]FfFfFfFfFf promptpromptJ/ψ fakeJ/ψ fakebbbbconv.conv.e fakee fake

lifetimeconstrain paramconstrain bkg LLLL

October 18, 2005 CDF-Japan meeting 16

J/+e data fit

c = 142.1 +21.9/-19.7 m

• The changes from input values (from fitting bkg sample) and returned values of final fitting are well within errors

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J/+e lifetime distribution

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Systematic uncertainty

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J/+e mass distribution

J/+trk with Lxy<-3 normalization : lifetime fit result

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Summary

• Bc lifetime measured with J/+e channel

0.474 +0.074/-0.066 0.033 ps

– References

• Run-I CDF (J/+e & J/+)

– 0.46 +0.18/-0.16 0.03 ps

• Run-II D0 (J/+)

– 0.448 +0.123/-0.096 0.121 ps

• Theoretical prediction

– 0.55 0.15 ps