Jochen Dingfelder, SLAC

Semileptonic Decay Studies

with BABAR

Annual DOE HEP Program Review, June 5-8, 2006, SLAC

B,D

,D,K,…

2

Study semileptonic B and D meson decays: B Xc,u l ,

D Xd,s l Leptonic and hadronic currents factorize!

Experimental approaches: inclusive or exclusive (B → lD→ Kl)

Semileptonic B and D Meson Decays

Exclusive Decays Low signal rate, better bkg

reduction

Need Form Factors to describe hadronization process

Measurement as function of q2, angles

Inclusive Decays Large signal rate, high bkg

Total rate calculated with HQE

Need Shape Function (b-quark motion in B meson) smears kin. spectra

SF param. from b s or b cl.

El q2 = pl

2+p2

MX

D,

electroweak interaction coupling |Vcb| , |Vub| or |Vcs| ,|

Vcd|

strong interaction meson structure

3

HQE fit theo. error band

|Vcb| from Ee and MX Moments

1st to 4th MX moments , 0th to 3rd Ee moments (as function of min. cut on Ee)

Enough d.o.f. to fit 8 parameters:Global fit to Ee , MX , E (bs) moments:

|Vcb| = (41.58 + 0.45 +0.58) x 10-3

mb (kin) = 4.591 ± 0.040 GeV

mp2 (kin) = 0.406 ± 0.042 GeV

needed for |Vub|

Measure moments of lepton momentum and hadronic mass spectra from B Xcl

|Vcb| @ 1.7%mb < 1%mc @ 5%

high mass

charm states

Mx2[GeV2/c4]

4

|Vcb| from B D* l Decay rate is:

f (1) = 1 in the heavy quark limit; lattice QCD says:

Shape of f(w) expressed by 2 (slope at w = 1) and form factor ratios R1, R2. Curvature from analyticity.

Measure decay angles l , V , . Fit3Ddistribution in bins of w to extact 2, R1, R2 .

Phase spaceForm factor

Here we use w = D* boost in B rest frame

0.0300.035(1) 0.919

FHashimoto et al, PRD 66 (2002) 014503

Caprini, Lellouch, Neubert Nucl. Phys. B 530, 153 (1998)

5

B D* l Form Factors & |Vcb|

stat. MC stat. syst.

Factor 5 improvement on FF uncertainty from previous CLEO measurement (1996!)

1D projections of fit result:

88M BB

w cosVcosl

Total systematic error on |Vcb| : 4.5% 3.5%

BABAR

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Inclusive |Vub| from Lepton Endpoint Study inclusive decays B Xul

Need to fight large charm bkg from B Xcl Low S/B need accurate bkg subtraction Restrict phase space (problematic for

HQE !) shape function becomes important

Select events with high-E lepton: 2.0 < Eℓ < 2.6 GeV Lower Eℓ cut below charm threshold Larger acceptance, smaller theoretical

error

|Vub|=(4.44±0.25exp ±0.22theo)10-3+0.42– 0.38SF

fully corrected

spectrum

BABAR

MC bkgb cl

Data

Data – bkg

MC signalb ul

88M BB

7

MX<1.67 GeV: |Vub| = (4.43 ± 0.45exp± 0.29theo)10-3

Hadronic B tag: Fully reconstruct one Btag in hadronic decay mode

know momentum, flavor, charge of other Bsignal

MX < 1.7 GeV and q2 > 7 GeV2

New “shape function-independent” approach: Combine b cl rate with b s spectrum Or measure full MX spectrum

Inclusive |Vub| with Hadronic B tag

|Vub|=(4.65±0.34exp ±0.23theo)10-3+0.46– 0.38SF

BBtagtag

BBsignalsignalXXuu ll

ee--

DD**

ee++

Leibovich, Low, Rothstein hep-ph/0005124,0105066

signal

theory uncertainties

Cut on MX

8

|Vub| from B l

Experimentally: Good S/B ratio, untagged & tagged

analyses Measure q2 dependence of form factor

Theoretically: Complementary to inclusive approach Form-factor norm. dominates error on |

Vub|

Untagged analysis: Reconstruct neutrino from missing 4-momentum of event

83 x 106 BB

disfavors ISGW IIquark model

|Vub| = (3.82 ±0.26exp ) 10-3+0.89– 0.53FF

Form Factor LQCD2

Data

Signal MC

Comb. Sig.

Crossfeed

bcl

qq

mES (GeV)

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Testing Theory with D K/l

|Vcs| from unitarity determine |

f+(q2)|

|f+(q2)| from LQCD determine |

Vcs|

Goal: measure ratio B(D l) / B(D Kl)

compare with lattice |f+(q2)| / |

f+K(q2)|

mpole = 1.854 ± 0.016 ± 0.020 pole = 0.43 ± 0.03 ± 0.04

D

Study D-meson decays from e+ e- cc with high statistics Tag one c quark via full reconstruction of D(*) meson Dramatically reduces bkg from u, d, s and B mesons

Charm SL decays provide high-quarlity lattice calibration.Techniques validated by charm decays can be applied to beauty decays!

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Form factor f (q2 = M2Ds) decay constant fDs

Leptonic decay proceeding through weak annihilation of quarks

DS and Decay Constant fDs

Ds → signal

N = 489±55Preliminary

230fb-1

stat syst Ds→

Aubin et al. PRL 95 122002 (2005)

(stat) 016.0135.0)(

)(

s

s

D

D

LQCD:

Validates LQCD predictions at 10% level

W , ,e

c

s

++=

+ + +|fDs|2

|Vcs|2

+ Reconstruct signal c quark via D*S DS

Normalize to Ds :

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Conclusions BABAR has broad program of semileptonic/leptonic B decays and dominates this sector. SLAC plays a leading role here.

Much progress in the last 1-2 years: |Vcb| 2%, |Vub| 7% , form factors, …

BABAR started to make use of their large D-meson samples Measurements of B and D semileptonic decays have reached precision to allow critical comparisons with lattice calculations: Form Factors & HQE Parameters

fDs results: CKM constraints (CP conserving) 2005 2006