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Bc lifetime measurement using BcJ/ e X channel

(Preblessing / cdfnote 7758)

Masato Aoki, Shinhong KimUniversity of Tsukuba

Ilsung Cho, Intae Yu SungKyunKwan University

Ting MiaoFNAL

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Introduction• We had measured the cross section of Bc in J/+e X

channel (note7518)– Electron ID using SoftElectronModule, dE/dx– Lxy>3sigma to kill prompt background– Background :

• Fake electron : estimate fake rate, J/+track as a control sample• Residual conversion : estimate conversion finding efficiency using

B0J/0, 0 or ee MC. Use J/+tagged conversion• b-bbar : use Pythia MC, B+J/K+ is used for the normalization• Fake J/J/ mass sideband subtraction

• We release the lifetime cut and measure the Bc lifetime– New background from prompt events

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J/+e selection cuts

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Summary of x-section measurement

M(J/+e) 3-4GeV 4-6GeV 3-12GeV

Fake e 16.200.322.77 15.430.312.52 34.380.475.72

Conversion 42.916.6820.89 14.544.386.39 63.178.3729.85

b-bbar 10.501.233.61 33.632.2011.17 55.922.8418.68

high mass excess 1.78 3.56 16.01

Total bkg 69.616.8321.45 63.594.9113.59 153.478.8539.10

DATA 96.0010.61 178.5014.67 313.0019.39

EXCESS 26.3912.6221.45 114.9115.4813.59 159.5321.3339.10

*Prompt BKG is killed by lifetime cut (Lxy>3sigma)

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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 BDl but with binning of

M(J/+e)

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Summary after releasing lifetime cut

Excess contains prompt BKG and Bc signal

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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/ : 0.209 +/- 0.012

• Statistical and systematic errors are included• Constrain the fractions for the final fitting using

Gaussian

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K-factor

1 20 1 20

1 20 1 20

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Additional cuts for the lifetime analysis

• Check Lxy distribution– B+J/K+

– J/+electron

• Use Lxy<70m

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Fitter check using B+J/K+

• Simply check our fitter using B+J/K+

• Result– c=504.1 9.3m

• Agree with blessed result from CDF

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Overview of background shape determination

• Fake electron : – J/+track with electron fake rates

• Fake J/ : – Sideband in J/+track candidates

• Residual conversion : – J/+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

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Fake electron • PDF for fake

electron BKG

)s|G(ct*)λ

*ct-(-ct*)Exp(λf

)s|G(ct*)λ

*ct(ct*)Exp(-λf

)s|G(ct*)λ

*ct(ct*)Exp(-λf

)s|)G(ct*f-f-f-(1F

-

-e fake

NJ/ fakeJ/ reale fakeJ/ realJ/ real ])Ff-(1F[f)G(fL

can be expected from J/ mass distribution: fake rateN : normalization factor

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

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fake J/ parameterization

• PDF for fake J/

)s|G(ct*)λ

*ct(-ct*)Exp(λf

)s|G(ct*)λ

*ct(ct*)Exp(-λf)s|G(ct*)

λ*ct(ct*)Exp(-

λf

)s|)G(ct*f-f-f-(1F -

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Fit results of fake electron & fake J/

table next page

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Fit results of fake electron & fake J/

: m

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Issue on fake J/ shape

• J/+track, conversion sample have fake J/ component as well as J/+electron

• Looking at fake J/+track, conversion, electron events, we found their shapes are similarsee next page

• Use common fake J/ shape• Use J/+track sample for every fake J/ shapes

– Limited stat. for conversion, electron samples

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J/sideband event comparison

similar shapes

J/+track

J/+electron J/+conv.-e

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Residual conversion

• PDF for residual conversion BKG

)s|G(ct*)λ

*ct(ct*)Exp(-λf)s|)G(ct*f-(1Fconv.

NJ/ fakeJ/ reale fakeJ/ realJ/ realconst param ])Ff-(1F[f)G(fLL

params of #

constrain param err)mean,|G(paramLConstrain fake J/ and scale factor

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Fit result of conversion BKG

Constrained using J/+track sample : m

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b-bbar background• PDF for b-bbar BKG

• Background events passing selection cut from each production process

1. Gluon splitting : 70%2. Flavor excitation : 25%3. Flavor creation : 5%

)s|G(ct*)λ

*ct(-ct*)Exp(λ

f-1

)s|G(ct*)λ

*ct(ct*)Exp(-λfF bb

Syst. study : GS and FE

(scaling factor is not constrained)

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Fit result of b-bbar BKG

: m

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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([

cτKH(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

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Signal fitting

c(Bc)=142.6 +22.2/-19.9 m

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signal fitting (cont’d)

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Systematic uncertainties

• K-factor– M(Bc), pT(Bc),lifetime(Bc),decay channel,…

• Background shapes– fake J/ 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/+X exclusive mode

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Systematics from K-factor

• M(Bc) 6.291, 6.251 GeV 142.4, 142.6 m c : 0.2 m

• (Bc) 0.4, 0.7 ps 142.3, 142.4 m c : 0.3 m

• HbJ/X spectrum 141.3 m c : 1.3 m

• Trigger simulation 142.8 m c : 0.2 m

• Inclusive BcJ/Xe channel (K factor next page)

142.1 m c : 0.5 m

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K-factor for inclusive Bc decays

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Systematics from background shapes

• Fake J/ : Use J/+e sideband137.5 m c : -5.1 m

• Res. conv. : Use J/+conv sideband145.1 m c : +2.5 m

• b-bbar : No error scaling in MC fitting

140.8 m c : - 1.8 m

s f + + -

1.0 fixed 0.916 +0.014/-0.015 172 +7/-6 61 +11/-9

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fake rate / finding efficiency weighting

Fake e : 141.2 m c : -1.4 m Conv. : 141.7 m c : -0.9 m

J/+track J/+conv.-e

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b-bbar : 100% FE, 100% GS

s f + + -FE 1.55 +0.17/-0.16 0.992 +0.005/-0.016 133 +10/-9 262 +607/-153GS 1.27 +0.24/-0.23 0.943 +0.018/-0.021 178 +9/-8 70 +23/-15

•100% FE 152.4 m : c = +9.8 m•100% GS 140.6 m : c = -2.0 m

: m

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Different resolution functions• Single Gaussian

• Double Gaussians

• Gaussian + symmetric exponential

Convolute

)]σs

ctExp(σs

1θ(-ct))σs

ctExp(-σs

1(ct)[ 21f

)s |)G(ct f-(1 RF

expexpexpexpexp

exp

)s|G(ctf)s |)G(ct f-(1 RF 222

)s |G(ct RF

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J/+track fit result for Gaussian+Symmetric Exp.

c(Bc)=136.5 m c : -6.1 m

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J/+track fit result for Double Gaussians

c(Bc)=136.2 m c : -6.4 m

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ct error distributions for Punzi effect

c(Bc)=138.0 m c : -4.6 m

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Systematics from ct resolution

• Resolution function c : -6.4 m

• Punzi effect (ct of fake J/, fake e, conv, others)

c : -4.6 m• Silicon alignment effect from note7409

c : 1.0 m

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Summary of systematic errorsCategory Description c (mm)

K-factor Bc mass 0.2

K-factor Bc lifetime 0.3

K-factor HbJ/X spectrum 1.3

K-factor Inclusive J/Xe 0.5

K-factor trigger simulation 0.2

Fake e No fake rate weighting -1.4

Fake J/ Use J/+e sideband -5.1

Res. conv. No finding efficiency weighting -0.9

Res. conv. Use J/+conv-e sideband +2.5

b-bbar Use FE only, GS only +9.8, -2.0

b-bbar No error scaling in MC fitting -1.8

Resolution Resolution function -6.8

Resolution Punzi effect -4.6

Resolution Silicon alignment 1 Total:+10.3/-10.0 m

1.5 m

+10.1 / -6.0 m

+1.0 / -7.9 m

K factor

BKG shapes

Resolution

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Summary

• We measured the Bc lifetime using J/+electron– c(Bc)=142.6 +22.2/-19.9(stat.) 10.3(syst.) m

or– (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

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Backup

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fake J/ with 2 negative exponentials

• Why fake J/ fit quality is so bad?complicated shape at ct<0 of fake J/ event

makes bad fit qualitytry to add one more negative exponential

– see next pageresult of Bc fitting: c(Bc) = 142.1 mthe effect of the negative side is –0.5 m

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fake J/ with different parameterization

w/ one negative exponential w/ two negative exponentials

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b-bbar : FE only fixing s=1.25

s f + + -FE 1.25 fixed 0.958 +0.032/-0.043 139 +11/-10 87 +150/-36FE 1.55 +0.17/-0.16 0.992 +0.005/-0.016 133 +10/-9 262 +607/-153GS 1.27 +0.24/-0.23 0.943 +0.018/-0.021 178 +9/-8 70 +23/-15

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For the lifetime measurement• Same cuts as Bc x-section measurement (note7518)• Mass window : M(J/+e)=4 ~ 6GeV/c2

• Background – fake electron : use J/+track– fake J/ : use fake J/+track– residual conversion : use J/+tagged conv.– b-bbar : Pythia MC– prompt : resolution function (Gaussian)

• Use common fake J/ shape for J/+track, J/+conv., J/+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)

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Gaus+Gaus && Punzi effect

• Resolution function is fixed using B+ events– RF parameters from B+J/K+ fitting

• s=1.271 +0.018/-0.017• fs2=0.10 +0.016/-0.014• s2=3.07 +0.18/-0.17

• J/+e fit result with new RF && Punzi term– c(Bc) = 131.4 +21.5/-19.2 m

c(Bc) = -11.2 m

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Gaus+Sym. Exp && Punzi effect

• Resolution function is fixed using B+ events– RF parameters from B+J/K+ fitting

• s=1.284 +0.015/-0.015• fexp=0.21 +0.03/-0.03

• sexp=1.70 +0.13/-0.11

• J/+e fit result with new RF && Punzi term– c(Bc) = 134.4 +21.8/-19.4 m

c(Bc) = -8.2 m