b lifetimes and flavour tagging at cdf run ii

Sinéad Farrington

University of Glasgow

for the CDF Collaboration

European Physical Society

Aachen, 17th-23rd July 2003

B Lifetimes and Flavour Tagging at CDF Run II

Sinead Farrington EPS Aachen 17th-23rd July 2003

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Outline

• Overview of B Physics at CDF

• B lifetimes:– Exclusively reconstructed B’s decaying via J/– Semileptonically decaying B’s

• Flavour Tagging


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B Physics at CDF Run II

pp collisions produce a wide spectrum of B hadrons in a challenging environment

Tevatron upgrade to 1.96 TeV CoM energy larger b production cross section

-


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B Triggers at CDF Run II

Di-Muon (J/) pT()>1.5 GeV/c J/ modes at low (conventional) pT( J/) 0 GeV/c

Measure x-section (See talk by Tara Shears)

J/ Yield=2x Run I

l + displaced track pT(e/)>4 GeV/c Semileptonic modes

pT(trk)>2 GeV/c Lifetimes,flavour tagging

120 m<d0(trk)<1mm B Yields 3x Run I

Two displaced tracks pT(trk)>2 GeV/c Hadronic modes

120 m<d0(trk)<1mm Charm Physics, B0s mixing

NEW!

(bb) << (pp) B events are selected with specialised triggers:

Indivdual data samples of about 140pb-1 accumulated

- -


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2 2

1 11 cosh 1 cos

2 2 2t tp p

e t mt eq q

B Hadron Lifetimes

According to the spectator model all B mesons would have the same lifetime…

but that is not the whole story!

The HQE predicts by how much the lifetimes differ. Objective 1: Measure lifetimes accurately to form input to theoriesObjective 2: Prove the detector and triggers are workingObjective 3: Measure s/s

B0slDs is an admixture of CP even and CP odd states

Pair it with fully CP even or CP odd state (or use polarisation analysis) and measure s/s

PDG Values


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B Hadron LifetimesEXCLUSIVE

J/ trigger •clean•fully reconstructed•lifetime unbiased•low statistics

J/

K+B+

SEMILEPTONIC

lepton+displaced track trigger •clean•partially reconstructed - need MC to unfold ct•lifetime biased•good statistics

•Reconstruct decay length by vertexing•Measure pT of decay products

T

xy

p

BmLc

B0 J/ K0*

B+ J/ K+

b J/ B0

s J/

B0 lD(*)-

b lc B0

s l Ds


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Fit Methodology:Simultaneous fit of M(B) signal fraction, define sidebandsc(B) lifetime

isig stGc

t

cF

,exp

1

),(

exp

expexp

)(1

ibkg stG

c

t

c

f

c

t

c

ff

c

t

c

f

tfff

F

Background Parameterisation:

Signal Contribution:

Exclusive BJ/X Lifetimes


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bJ/ Lifetime and Crosscheck

CONTROLSAMPLE


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Exclusive BJ/X Lifetimes: B0s Meson

CDF Run II Preliminary

B+ 1.630.050.04 ps

B0d 1.510.060.02

ps

B0s 1.330.140.02

ps

b 1.250.260.10 ps

B0s J/ is mostly CP even

measures mostly L componentAccess s/s via angular analysis – coming soon

World’s largest sample of fully reconstructed Bs mesons


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Extraction of Semileptonic LifetimesLepton+ displaced track trigger implemented successfully for the first time! samples rich in B hadron semileptonic decays

Follow the standard methodology:•reconstruct the D decay near to lepton•B decay not fully reconstructed extract the factor from Monte Carlo: • extract lifetime from decay length:

but with one crucial complication: lifetime bias from the displaced vertex trigger:4 GeV lepton + 2 GeV track with 120 m<d0 <1mm

Emulate trigger with Monte Carlo and model the lifetime bias which is factored into the fit function.

0 0

0 0

( ) ( ) ( );

( ) ( ) ( )xy s xy s t s

t s t s t s

L m B L m B p lDc K K

p B p lD p B


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K Factor and Bias from MCK Factor Distribution P(K) Reconstruction efficiency including trigger

bias, as a function of proper lifetime

Normalised to unit area

Arbitrary vertical scale


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B Semileptonic Channels

M(pK) (GeV/c2)

apply PID

CDF Run II Preliminary 70pb-1

b lcl

DsD


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Semileptonic Decay Fit ModelUnbinned maximum likelihood fit to c(B)

– Background is parameterised by delta function and positive exp convoluted with Gaussian resolution:

Free parameters: D E + f+ G

– Signal: exp convoluted with Gaussian resolution, K factor distribution, P(K), and bias function,

– Maximum likelihood function:

),(exp)(1 GE

Dbkg tGtf

tfF

)(),()(exp KPstGKtKt

c

KNF isig

bkgsig N

j

jbkg

N

i

ibkgbkg

isigbkg FFfFfL 1


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Semileptonic Lifetime Fits

b c

Lifetime statistical error projections

B+ 0.04 ps

B0d 0.06 ps

B0s 0.07 ps

b 0.09 ps

Highest statistical accuracy lifetime fits in B0s and b:

Control Samples •Fit results show discrepancy with world average •Many crosschecks•Currently working to understand all effects of trigger bias etc.

CDF Run II Preliminary 70pb-1

B0s Ds

ct(B)(mm)


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Flavour Tagging Development

OPPOSITE SIDESoft Lepton Tag* Opposite side K Tag Jet charge tag

OPPOSITE SAME

SAME SIDESame side K/ Tag*

TAGWR

WR

WR

WR

PDNN

NNA

mtDtNtN

tNtNtA

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cos)()(

)()()(

• Determine B flavour at production and decay to measure

– B0 mixing, B0s mixing, CP violation

• Figure of merit: D2

– : tag efficiency– D: Right-Wrong/Right+Wrong

• CDF has a battery of tags which arebeing developed further


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Same Side Tag Asymmetry

• Identify fragmentation pion• Measure raw asymmetry:

• Test tagger on B+ should see NO oscillations!

B lD0 B+ J/K+

For B0s mixing apply same side K tag: very powerful

)()(

)()()(

tNtN

tNtNtA

WR

WR


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Tagger Studies in Semileptonic Samplelepton + displaced track trigger provides high statistics sample of ~150000 B (and D) semileptonic decaysStrategy:• trigger lepton estimate of B flavour at production• count numbers of opposite side tags• can subdivide sample by muon system and pT

rel

• parameterise relative dilution for use in likelihood fit• cross check consistency with partially reconstructed lepton+D+,0

• consistent results believe dilution in lepton+Ds

• This number is UNBIASED since we’re using an independent (and high statistics) control sample

trackp(e/+D)

P.V.

Detailed sample composition studies:– Mass cut removes D decays: 2<M(l+track)<4GeV/c2

– Background subtraction variable separates B’s from background: signed IP of displaced track


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Soft Muon Tag D2

Soft Muon Tagger D2=0.6600.093 % CDF Run I: D2=0.584 0.082 %

Identify charge on opposite side

Sufficient statistics to examine parameterisation of dilution as function of pT

rel

•Method will be used to evaluate, optimise and compare all taggers

•Unbiased way of optimising taggers

•Next step: measure D2 for a reconstructed channel

Background subtraction has been used to obtain measurement of D2


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Summary• Lifetime measurements made in clean BJ/ channels:

• Lepton + displaced vertex trigger has been implemented at CDF for the first time– lifetime measurements ongoing: will give best statistical accuracy in B0

s and b

– Flavour Tagging procedure has been established and two taggers have been optimised and evaluated in a non-biased way

• Measurements of s/s coming soon and first steps towards B0s mixing are

happening!

CDF Run II Preliminary

B+ 1.630.050.04 ps

B0d 1.510.060.02

ps

B0s 1.330.140.02

ps

b 1.250.260.10 ps


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K Factor and Bias from MCELECTRONS:


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Major upgrades at CDF provide•Increased geometric coverage•Extended muon system•new 3D silicon tracker•faster response drift chamber•Triggers: large bandwidth, background reduction, displaced vertex triggering


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• Determine B flavour at production and decay to measure

– B0 mixing, B0s mixing, CP violation

• Figure of merit: D2

– : tag efficiency– D: Right-Wrong/Right+Wrong

• CDF has a battery of tags which arebeing developed further

• Run II’s lepton+displaced vertex trigger large sample of semileptonic decays • allows us to measure , D and D2 in data and optimise the taggers• can then apply them in any sample without bias


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b lifetimes and flavour tagging at cdf run ii

Documents

b triggers

dssinead farrington

pssinead farrington

b mesons

b j b0s j b0 ld

b lc b0s

b hadron lifetimesexclusivej

outlineoverview of b