stato di vub e vcb

Stato di Vub e Vcb

Concezio BozziINFN Ferrara

Babar Italia, Trieste 14 Aprile 2005

Sommario

• Decadimenti semileptonici inclusivi– con charm (Vcb)– senza charm (Vub)

• Decadimenti semileptonici esclusivi– l, l (nuovi risultati, Moriond&CKM05)– D*l

• NB: ho attinto a piene mani da materiale presentato (da altri ma anche da me!) a CKM2005

Misure inclusive

Inclusive Decays – the Big Picture

43

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2

332

45

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3322

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23

52

1)()1(2)),(1(

21),(1)(

1||192

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bb

D

b

b

LSDG

pert

b

b

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EWcbbF

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mO

mr

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mrrA

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mrAr

AVmG

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Semileptonic B Decays & HQE

contains b- and c-quark masses, mb and mc

2 related to kinetic energy of b-quark

G2 related to chromomagnetic operator: B / B* mass splitting

Darwin term (ρD3) and spin-orbit interaction (ρLS

3) enter at 1/mb3

= scale which separates effects from long- and short-distance dynamics

r = mc/mb; z0(r), d(r): phase space factors; AEW = EW corrections; Apert = pert. corrections (sj , s

k0)

No 1/mb term!

Several HQE schemes exist; op’s and coeff’s are scheme dependent

free-quark rate

Inclusive bcℓν Measure electron momentum spectrum and mass of

hadronic system in SL decay

Determine moments to allow comparison with parton-level calculations (duality assumed)

Calculations exist for the following:

Fit for HQE parameters and |Vcb|

),,,,,,( 33220

00LSDGcbnE

nlBEE

nl mmEfdEE

l

),,,,,,( 33220

00LSDGcb

xnE

nXBEE

nx mmEfdMM

l

Mass of hadronic system

Lepton energy spectrum

Gambino & Uraltsev (hep-ph/0401063, 0403166)

Fit Results

mX moments

Eℓ moments

● = used, ○ = unusedin the nominal fit

Red line: OPE fitYellow band: theory errors

BABAR

2/ndf = 20/15

BABAR PRL 93:011803

Fit Results

Impressive agreement between data and theory

≈ identical results obtained in another renorm. scheme: Bauer, Ligeti,

Luke, Manohar, Trott in hep-ph/0408002

s

s

s

3exp HQE th

exp HQE

exp HQE

exp HQE

2 2exp HQE

2exp HQE

(41.4 0.4 0.4 0.6 ) 10

(10.61 0.16 0.06 )%

(4.61 0.05 0.04 0.02 )GeV

(1.18 0.07 0.06 0.02 )GeV

(0.45 0.04 0.04 0.01 )GeV

(0.27 0.06 0.03 0.0

cb

c

b

c

G

V

m

m

B

s

s

s

2

3 3exp HQE

3 3exp HQE

2 )GeV

(0.20 0.02 0.02 0.00 )GeV

( 0.09 0.04 0.07 0.01 )GeV

D

LS

kinetic mass scheme with μ=1 GeV

Fitted values consistent with

external knowledge

2/ndf = 20/15

Uncalculatedcorrections to

BABAR PRL 93:011803

precision on mb = 1.5%

precision on |Vcb| = 2%

2% accuracy!

Inclusive |Vcb| status

BaBar result compared with previous measurements:

Agrees with value coming from exclusive BD* ℓ ν

decays (from HFAG):3

expt theo(41.4 1.0 1.8 ) 10cbV

Inclusive bu Limiting factor in CKM precision tests; known much

less well than |Vcb|

CKM suppressed – therefore harder to measure

Challenge for experiment and theory

Starting point: HQE Just like bcℓν…, and with similar accuracy

…until limited expt’l acceptance is considered

Poor convergence of OPE in region where bcℓν

decays are kinematically forbidden

Non-perturbative Shape Function must be used to

calculate partial rates

= scale which separates effects from long- and short-distance dynamics

AEW = EW corrections; Apert = pert. corrections (sj , s

k0)

32

2

52

22

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3

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21)(1||

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bb

Gpert

b

Gpertub

bFEWu m

Om

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AXB

Theory input• Reference (ICHEP04, HFAG) results based on triple differential

decay rate (Ee, mX, q2) computed to O(s, mb-2) over the entire phase

space by de Fazio and Neubert (DFN, JHEP 06:17 (1999))• Use as input the shape function parameters determined by a fit

(hep-ex/0407052) to the Belle b→s spectrum:

Λ = 0.66 GeV, λ1 = -0.40 GeV2 + covariance

δΛ ~ δmb ≈ 80 MeV

• q2 vs mX analysis: take acceptances from Bauer, Ligeti and Luke (BLL, hep-ph/0111387), OPE calculation in a region of the phase space where SF effects are small.

f(k+) Acceptance in

b → uℓv

E spectrum in

b → s

0 4( ( ) (1.22 0.26) 10 )B B l

Inclusive Vub measurements with BaBarInclusive Vub measurements with BaBarmethod S/B Pros&Cons Vub(x10-3)

Electron spectrum endpointEe>2.0GeVTotal rate using DeFazio-Neubert

0.050.2

•High statistics•Duality valid for

tight Ee cuts?

•Bkg subtraction

Ee vs q2 and neutrino reconstructionEe>2.0GeV and sh<3.5 GeV2/c4

Total rate using DeFazio-Neubert

~0.5

•High statistics•Lower syst. on

shape functions•Bkg subtraction

mX analysis (1-D)mX<1.55 GeV/c2

Total rate using DeFazio-Neubert

~1.7

•Low background•High resolution •Low statistics•Shape func. syst.

mX vs q2 analysis mX<1.7 GeV/c2 and q2 >8.0 GeV2/c4 Vub using Bauer et al.

~2

•Low background•Very small syst.

on SF param.•Small statistics

Total rate using Form Factors calc.

120•Very small bkg•~no cut on kinem•Small statistics

UntaggedUntagged

UntaggedUntagged

Partial TagsPartial Tags

Breco TagsBreco Tags



exclusiveCurrent Vub errors: 10-15% Total experimental syst @250-500 ifb: 3-6%

4.40 ± 0.24exp ± 0.35theo

4.99 ± 0.48exp ± 0.29theo

5.22 ± 0.43exp ± 0.33theo

5.18 ± 0.57exp ± 0.34theo

Vub measurementsVub measurements

A different theory approach

• Bosch, Lange, Neubert and Paz (BLNP)

Nucl. Phys. B 699, 335 (2004)

• Acceptances computed in BLNP using SF parameters from – Belle b→s

hep-ex/0407052

– BaBar b→cℓ moments (hadronic and leptonic)

hep-ex/0404017

• Proper translation into shape function scheme of BLNP

hep-ph/0412241

Courtesy of Henning Flächer

Results with BLNP and BaBar b→cℓ moments

Using mb = 4.63±0.08 GeV and μπ2 = 0.15±0.07 GeV2 (SF scheme) with

correlation coefficient -0.4. Errors are: expt ± SF ± theory expt ± (SF+theory)

Method ∆B × 104 |Vub| (BLNP)

SF params from bcℓν

|Vub| (BLNP)

(Belle SF) |Vub| ICHEP

(DFN, Belle SF)

Endpoint 5.31±0.59 3.93 ± 0.34 ± 0.38 ± 0.18 (8.7 ± 9.7 ± 4.6)% 4.55

4.40 ± 0.24 ± 0.35

( ± 6.4 ± 8.6) %

q2-Ee 4.46±0.93 3.89 ± 0.40 ± 0.45 ± 0.21

(10.3 ±11.5 ± 5.4)% 4.534.99 ± 0.48 ± 0.29

( ± 9.6 ± 5.8) %

q2-mx 8.96±2.04 4.45 ± 0.49 ± 0.40 ± 0.22

(11.1 ± 9.0 ± 4.9)% 5.005.18 ± 0.57 ± 0.34

( ±11.0 ± 6.5) %

Average 4.07 ± 0.51 4.61 ± 0.46

b→cℓ moments: significant change in inclusive |Vub| valuesBLNP: increased sensitivity to SF

Misure di Vub esclusive

03/16/003/16/055

Jochen Dingfelder – CKM Workshop 2005

Exclusive B Xul Decays Exclusive B Xul Decays

▪ Goal : Measure Branching Fractions and |Vub|

▪ Need FF predictions to describe QCD effects

New unquenched LQCD calculations (HPQCD’04, FNAL’04)

Try to measure q2 dependence of FF with data


Semilep.TagsSemilep.Tags

UntaggedUntagged

l-

Y(4S)Y(4S)

Xu = +, 0,+, 0, ’, a0

0, a0+

low bkg, low stat.: 27,… (ICHEP’04)Balance between

efficiency and purity

High statistics, highhackground (b cl)

3 newl

results

03/16/003/16/055


Semileptonic Tag AnalysesSemileptonic Tag Analyses Reconstruct B D(*)l and study

semileptonic recoil use both D and D* tags sizable BF

Tagging efficiency measured with “Double Tags” (two D(*)l)

Correct sl. decay |cosBY| < 1

( tag side: cosBY, signal side: cosB,l )

cos2B < 1 for signal, bkg flat

D(*)ldeca

ys

03/16/003/16/055


0lwith SL Tag : Signal Extraction

0lwith SL Tag : Signal Extraction

Cut-and-count analysis in cosB,l and mD

Signal region: -1.1 < cosBl < 1.0

Subtract mD sidebands remove cominatoric background

Subtract other background using MC normalized in -10 < cosBl < -1.5

82 fb-

1

45 0

03/16/003/16/055


+l with SL Tag : Signal Extraction

+l with SL Tag : Signal Extraction

Extract signal yields by binned fit to cos2B in 3 bins of q2:

Fit parameters = signal and background normalizations

211 fb-1

21 + 26 + 14 +

≈ 30% l X-feed

Mainly B0B0

bkg

03/16/003/16/055


+l with SL Tag : Branching Fractions and q

+l with SL Tag : Branching Fractions and q

SL tag analyses statistically limited.

Yields not yet large enough to discriminate between FF models.

03/16/003/16/055


Neutrino Reconstruction: Reconstruct from full event & ensure

good reco. quality

Untagged B l and B l Untagged B l and B l

Fit all 4 signal modes simultaneously (+, 0, +, 0) Use isospin relations to reduce number of signal

parameters: (B0 -l+) = 2 (B+ 0l+) (B0 -l+) = 2 (B+ 0l+)

Max-LH fit of signal and background in E, mES, and q2

Harsh suppression of b cl bkg (kinem. cuts, mainly for l) e+e- qq bkg (topological cuts)

Cut on missing mass: |M2miss / 2Emiss| < 0.4 GeV

03/16/003/16/055


Untagged l: Fitted E and mES


76 fb-

1

427 , 147 0 5 bins for l3 bins for l

03/16/003/16/055




5 bins for l3 bins for l101 , 104

0

76 fb-

1

03/16/003/16/055


Recent LQCD and LCSR calculations agree well with data

ISGW2 shows marginal agreement for l

Errors forl still too large to study 3 form factors.

Measured q2 Distributions and Form Factors

Measured q2 Distributions and Form Factors

l l

03/16/003/16/055


Systematic Uncertainties (Untagged)

Systematic Uncertainties (Untagged)

Better statistical precision than previous measurements

Syst. error dominated by reconstruction. Will decrease with improved track/neutral reconstruction.

Results less dependent on theoretical predictions (own FF measurement)

03/16/003/16/055


Overview: Branching Fraction Measurements

Overview: Branching Fraction Measurements

Testing isospin symmetry:

Measure +l, 0l separately (untagged)

l l

03/16/003/16/055


Extraction of |Vub|Extraction of |Vub|

Measurement in bins of q2 allows extraction of |Vub| for various q2 regimes and FF calculations :

LCSR q2 <15 GeV2, LQCD q2 > 15 GeV2 or extrapolation to whole q2 range

Quote LQCD2 asrepresentative

Misure di Vcb esclusive

Ultimate solution: combined measurement of form factors and Vcb! (work in progress in Trieste)

Other ideas?• D*0l (little/undermanned efforts)• Yet another measurement of D*+l

– D* partial reconstruction– On the recoil of a fully reconstructed hadronic decay

Run1-4

M. Andreotti

PhD thesis

Conclusioni• Mole impressionante di risultati sperimentali e teorici• Collaborazione virtuosa tra le due comunità• Effetto complessivo:

– Vcb inclusivo: ~1.5%• Accordo impressionante teoria-esperimenti!

– Vub inclusivo: 10% → 5% ?• Aggiornare misure con tutta la statistica disponibile• Ampio consenso teorico sulla validità delle relazioni

b→cℓν b→s b→uℓν• Un po’ meno sulle incertezze relative

– Vub esclusivo: • Occorre più statistica e migliorare le sistematiche sperimentali• calcolo dei fattori di forma non ancora pienamente maturo

– Vcb esclusivo: 4% → ?• Nuove misure (Dl) per limitare incertezze teoriche e per risolvere

l’accordo marginale tra le misure esistenti (D*l)

stato di vub e vcb

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