First Measurement of the Ratio B ( L b L c mu )/ B ( L b L c p ) at CDF

First Measurement of the Ratio B(b c)/B(b c)

at CDF

Shin-Shan Yu

University of Pennsylvania

SLAC Experimental Seminar, August 11th, 2005

http://www-cdf.fnal.gov/physics/new/bottom/050407.blessed-lbbr/

CDF

August 11th, 2005 Shin-Shan Yu 2

Outline

Why b

CDF Detector, Triggerb Relative Branching Fractions

budb


Big Picture : Why b Baryon?

u d b


Experiment B(b c)/B(b c) ?

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

Relative BR is the yield ratio corrected for the efficiency, e.g:

cbcb

cbcb

NN

cb

cb

)()(

BB

cbcb

cbc

NNN XB

cb

cb

)(

)()( bgmix

BB

)()(

0

0

DBDB

BB

)()(

*0

*0

DBDB

BB

and

But since we can not reconstruct neutrinos, several backgrounds can fake our semileptonic signals in the data ….


CDF Detector & TriggerSilicon Tracker

|| < 2vertex ~ 30 m

Central Outer Tracker (COT)

96 layers drift chamber, up to ||~1PT /PT~ 0.15% PT

Central Muon Chamber4 layers drift chamber outside the calorimeter|| < 0.6

Two Displaced-track Trigger pT > 2 GeV/c, 120 m ≤ d0 ≤ 1 mm,

Lxy > 200 m, pT > 5.5 GeV/c 150 M events analyzed for this

measurement


Signal Sample b cX c p+ K- + Inclusive Semileptonic Signal Hadronic Signal

Background shapes come from MC

NDF=36.6/42Prob=70.7%


Control Sample DX, D+ K-+ +


Hadronic SignalInclusive Semileptonic Signal


Control Sample D*X, D*+ D0 +, D0 K-+ Inclusive Semileptonic Signal


Hadronic Signal


MC and Data Comparison: Before 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(b), M(c)

PT(b) [GeV/c] M(c) [GeV/c2]


MC and Data Comparison : After


Physics Backgroundb-hadron -> …. -> c additional particles e.g:

Reduced by the M(c) cut

Where Are the Semileptonic Backgrounds from?

c

cb

)2593(

hadronichadronic

physicsphysics

hadronic

physics

B

Bi

NN

Normalize the amount to the measured hadronic signal

BRs come from PDG, theoretical estimate and preliminary measurements

~10% contribution


First Observation of b Semileptonic Background

c++

CDF Run II Preliminary 360 pb-1


c(2593)

c(2625)


Xcb 0

c0

Xcb

Xcb *

Estimated BR of the reconstructed background based on the first observation

PDG BR(b -> c X)=9.2%

c++,+,0

c(2625)c(2593)


084.0236.0

dff

I Run CDF b

BR) ( 22.0)( 11.0 (stat) 08.082.0)()(

)/ 6()/ 6(

II Run CDF 00

ccb

TB

T systDBcGeVP

cGeVPb

BB

db

b

ff

b

How to Obtain B(b c Make use of previous CDF measurements

b MC PT spectrum using fully reconstructed decay was not available for CDF I

Correct the CDF I flambdab/fd using measured PT spectrumAcceptance correctionDifferent PT thresholds affect the ratio 10 GeV/c vs. 6 GeV/c

% )( 08.006.0

)(stat 19.041.0)(

pTsystcb B

)( 11.019.0

)(stat 20.056.0) 6() 6(

GeV/c

GeV/c

0

pTsystPP

TB

Tb

Consistent with the prediction 0.45% (Phys. Lett. B586, 337)


How to Obtain B(b c


?

Where Are the Semileptonic Backgrounds from?Muon Fakes

p, K, fake muonscand muon d0 cuts suppress prompt fakes

Our fakes mostly come from b decays

Weight “c+TRKfail” events with the Pfake

p, K, fractions from the inclusive B MC~5% contribution


Where Are the Semileptonic Backgrounds from? QCD Pair Production:

charm and from different b- or charmed hadronsSuppressed due to the cand PT() cuts

Rely on Pythia MC Most sensitive to gluon splitting ~0.2% contribution

ccbb ,

c+

p+

p+

c+


Inclusive Semileptonic Sample Composition 3.2%

9.8%

86.8%

0.2%

Signal Physics Fake mu ccbar,bbbar

4.9%

40.0% 53.9%

1.2% 4.3%

15.0%

79.8%

0.9%

XB cmix XDB mix XDB *mix


Consistency Check


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 (b c b semileptonic decay model

size of the independent MC for reweighting the phase space distribution uncertainty on the predicted form factors


Uncertainty Summary fractional uncertainty (%)

Measured BR +3.5 -10.5 8.2 2.3Estimated BR 2.5 9.2 6.2CDF Internal

Mass fitting 3.2 4.1 < 0.1

Muon fake 0.9 0.7 0.4

Pt spectrum +1.4-2.5 3.2 2.2

CDF material 1.1 1.7 1.3 scaling 0.4 0.5 0.4

0.2 2.2 1.3

b,c polarizations 1.9 -- --

c Dalitz 0.4 -- --

b lifetime 1.1 -- --

b decay model 2.9 -- --

6.0 6.1 3.4Statistical 15.0 10.2 13.0

ccbb ,

))

0

0

DBDB

B(B(

))

*0

*0

DBDB

B(B(

))

cb

cb

B(B(

Physics background and hadronic signal branching fractions

MC modeling of efficiency and acceptance


Control Sample Result

(UBR) 0.9(BR) 0.8(syst) 0.6(stat) 0.18.9))

0

0

DBDB

B(B(

Consistent with the 2004 world average 7.8 1.0 at the 1level New world average ratio 8.3 0.9

(UBR) 1.1 (BR) 0.4 (syst) 0.6 (stat) 3.27.17))

*0

*0

DBDB

B(B(

Consistent with the 2004 world average 19.7 1.7 at the 0.7 level New world average ratio 19.1 1.4


Signal Sample Result

(UBR) 0.5 (BR) 2.1-0.7

)(2.1 (stat) 0.30.20))

systcb

cb

B(B(

Experimental Uncertainties dominated by:

Data sample size

B (b c

CDF Run I fbaryon/fd

B(c->pK)


What Do We Know about b Now?

c l (5.0 1.9) %c l c

20.0 3.7c(2593) +

l seenc(2625)

+l seenc

++ l

seenc

0 l

seen

DELPHI(Phys. Lett. B585, 63)

(4.1 2.0) x 10-

3

Back Up Slides


Heavy Quark Effective Theory (HQET) simplifies the calculation of b-hadron BR

Assuming mb >> QCD Corrections expressed in the power

of 1/mb and s(mb)

Spin of light degrees of freedom = 0, the corrections are simpler than those of b-mesons.

%45.0 )(

% 6.6)(

theorycb

theorycb

BB

q ud

0s


Physics Background


MC Tuning

Flat phase space

Form factor weighted


b Polarization

cos1

cos bddN

First Measurement of the Ratio B ( L b L c mu )/ B ( L b L c p ) at CDF

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