alex smith – university of minnesota determination of |v cb | using moments of inclusive b decay...

Alex Smith – University of Minnesota

Determination of |Determination of |VVcbcb| Using Moments of Inclusive B | Using Moments of Inclusive B

Decay SpectraDecay Spectra

BEACH04 ConferenceJune 28-July 3, 2004

Chicago, IL

Alex Smith

University of Minnesota

Introduction Hadron Mass Moments in BXcl Lepton Energy Moments in BXcl Photon Energy Moments in BXs decays

Combined Fit to Determine |Vcb| and HQET parameters

Summary


Measuring |VMeasuring |Vcbcb||

• |Vcb| is a fundamental parameter of the Standard Model

• Inclusive semileptonic bc transitions provide a good laboratory in which to measure |Vcb| – Exclusive semileptonic modes suffer large theoretical uncertainties– Purely hadronic final states too complicated– Weak bcl process still obscured by strong interactions

• Strong interactions of inclusive semileptonic decays described by– Perturbative QCD

• Short-distance effects

– Heavy Quark Effective Theory/Operator Product Expansion• Non-perturbative long-distance effects


Heavy Quark Effective TheoryHeavy Quark Effective Theory

• Semileptonic rate expressed as a double expansion in s and 1/mb

– Use “kinetic mass” formulation of Uraltsev, et al (hep-ph/0401063)

33223

252

,,,,,,,1192 LSDGcbm

ms

cbbF mmNPVmG

cbc

b

couplingorbit -Spin :

TermDarwin : /1

)( splitting Hyperfine :

)(quark of momentum Fermi : /1

)( massquark : /1

massquark :

3

33

22

122

LS

Db

G

b

bb

c

mO

bmO

bmmO

cm


Moments of Observable SpectraMoments of Observable Spectra

• Moment of distribution defined in usual way:

• A commom set of HQET parameters appear in expressions for– Lepton energy moments in BXcl– Hadronic mass-squared moments in BXcl– q2 moments in BXcl– Photon energy moments in BXs– Semileptonic width

• Simultaneously fit these measurements to determine HQET parameters

cut

cut

E

E

n

cutn

dEdE

d

dEdE

dE

EE

)(eg., lepton energy moment:


The CLEO II DetectorThe CLEO II Detector

• CESR symmetric e+e- collider– Energy near (4S)

• Most relevant features of detector:– Hermeticity of detector

neutrino reconstruction– Excellent shower

resolution of CsI calorimeter photons, electrons

– Good charged particle resolution and dE/dx of drift chamber leptons


Hadronic Mass and Hadronic Mass and qq22 Moments in Moments in BBXXccll

Infer hadronicmass

Reconstructneutrino

Identifylepton

B

X W

l

Wl

qMX

El

E

UnknownSmall

beam222 cos22 BBBX pppEEEqMM

• Neutrino reconstruction technique

hep-ex/0403052



Infer hadronicmass

Reconstructneutrino

Identifylepton

B

X W

l

Wl

qMX

El

E

UnknownSmall

beam222 cos22 BBBX pppEEEqMM

• Neutrino reconstruction technique



• Selection criteria applied to suppress continuum and enhance neutrino reconstruction

• Fit differential decay rate in three dimensions:– q2

– MX2

– cosWl

• Fit Components and models:– BDl HQET+measured FF’s– BD*lHQET+measured FF’s– BD**lISGW2– B(Xc)non-reslGoity-Roberts– BXulISGW2+NR– Secondary leptons CLEO MC– Continuum and fakes data

Note: histogramsnormalized to same area

Fit Components



• Fit projections– Fit provides reasonable

description of the data

• Branching fractions of individual modes are very model-dependent

• Inclusive differential decay rate much less model-dependent

q2 MX2

cosWl |pl|

E



• Results are consistent with previous CLEO measurements

• Uncertainties and results comparable to BaBar measurements

• q2 moments expected to be somewhat complementary to MX moments– Only measured by CLEO

hep-ex/0403052


Lepton Energy Moments in Lepton Energy Moments in BBXXccll

• Di-lepton event sample• Use one lepton as the “tag”:

– pl > 1.4 GeV/c, e or – ~97% of sample is primary

BXl– Lepton charge tags flavor of

parent B meson

• Look for signal electron in “tagged” events– pe > 0.6 GeV/c– Correct for backgrounds and

efficiencies– Use charge and kinematic

correlations to separate the spectra from primary and secondary leptons

• Primary leptons are the signal

Monte Carlo simulation of electron daughters from B decay

hep-ex/0403053



Unmixed B0 Mixed B0

Primary EventsOpposite B SecondariesSame B Secondaries

ebb ecbb

ecb

ebb ecbb



Unmixed B0 Mixed B0

Primary EventsOpposite B SecondariesSame B Secondaries

ebb ecbb

ecb

ebb ecbb

Easily vetoed with kinematic cut

X25 rejection66% efficient



• Subtract backgrounds• Correct for efficiencies• Algebraically solve for

primary spectrum

1

1

b opp

b sameb opp

dp

cdB

dp

bdB

dp

edN

dp

cdB

dp

cdB

dp

bdB

dp

edN



• Correct for – EW radiation– B boost

• Results consistent with previous CLEO measurements• Systematics-limited--- Uncertainty on moments comparable to BaBar• Integrate measured spectrum

%24.009.091.10 XeBBR

hep-ex/0403053


Photon Energy Moments in Photon Energy Moments in BBXXss

• Large photon background from continuum processes– 0 and veto– Suppress using neural network

• Several different inputs related to event shape

– Pseudo-reconstruction• Ks

0 or K+/-

• 1-4 pions, at most one 0

– Large subtraction necessary

222 GeV 0020.00066.00226.0

GeV 011.0032.0346.2

EE

Ehep-ex/0108032


Photon Energy Moments in Photon Energy Moments in BBXXss

• bs measurement is key to extracting HQET parameters– Sensitive to mb

• Mean energy (1st moment) roughly equal to mb/2

– Independent of mc

• New analysis in progress– Previous analysis optimized for branching fraction

measurement– New analysis of old data optimized for extraction of

spectrum– New results soon


Combined Fit to Determine |VCombined Fit to Determine |Vcbcb||

• Measurements included in fit: – 1st and 2nd photon energy moments : E > 2.0 GeV

– 1st and 2nd lepton energy moments : Ee > 0.7, 1.2, 1.5 GeV

– 1st and 2nd hadronic mass moments : Ee > 1.0, 1.5 GeV

– 1st q2 moment : Ee > 1.0, 1.5 GeV

• Chi-squared fit including full correlation matrix of measurements

• Uses O(1/m3) formulation and code from Uraltsev and Gambino (hep-ph/0401063)

– Includes perturbative corrections to account for lepton/photon energy cuts

• Will also use approach of Bauer, Ligeti, et al before finalizing results (hep-ph/0210027)



CLEO data

(GeV/c2)

(GeV

2 )



1st and 2nd LeptonEnergy Moments

CLEO data

(GeV/c2)

(GeV

2 )



1st and 2nd PhotonEnergy Moments

CLEO data

(GeV/c2)

(GeV

2 )



1st and 2nd HadronicMass Moments

CLEO data

(GeV/c2)

(GeV

2 )



1st q2 Moments

CLEO data

(GeV/c2)

(GeV

2 )



• Only CLEO has measured photon energy, q2, hadronic mass, and lepton energy in a single experiment– A solution consistent with all measurements is found

– Without BXs mb and mc almost completely correlated in fit

– Most of the sensitivity to mb comes from BXs measurement

• First moment mean photon energy mb/2 (approx.)

• Other measurements primarily constrain mb-Cmc, C~0.6

– q2 moment gives some complementary information• Nearly independent of

2



CLEO data

(GeV/c2)

(Ge

V/c

2)



1st Lepton EnergyMoment

2nd Lepton EnergyMoment

1st Photon EnergyMoment

2nd Photon EnergyMoment



2nd Hadronic MassMoment

1st Hadronic MassMoment

1st q2 Moment



measurement key



• Measurement of |Vcb| and HQET parameters, including mb(), mc(),

() at =1 GeV

• Expect to reduce experimental errors significantly with additional measurements

• Theory errors under study and not shown or included in fit– Expected to be >= experimental

errors33

3026.0029.0

3

2083.0081.0

2

2050.0054.0

2

210.011.0

2073.0074.0

GeV 17.005.0

GeV 091.0~GeV 10.0

GeV 483.0

GeV/ 16.1

GeV/ 564.4

LS

D

G

c

b

cm

cm

3108.04.42 cbV


SummarySummary• Potential to significantly improve measurement of |Vcb|

– Experimental errors expected to be less than 2%– Theoretical errors expected to be comparable to experimental errors– Theoretical models will benefit from experimental constraints on higher

order parameters

• Many improvements to analysis in progress:– 3rd lepton energy moments– work in progress– Include more 1st and 2nd lepton energy moment measurements in fit– 2nd q2 moments – should have corrections soon

• Complementary sensitivity to parameters

– Improved BXs moments – soon• Critical constraint on mb

– Include theoretical uncertainties in fit– almost ready

• CLEO has measured several different moments in a single experiment– Complementary to and of comparable precision to public BaBar

measurements

alex smith – university of minnesota determination of |v cb | using moments of inclusive b decay...

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