Semileptonic and EW Penguin Decay Results from BaBar

John J. WalshINFN-Pisa

BaBar Collaboration

XXXXth Rencontres de Moriond

QCD and Hadronic InteractionsLa Thuile, Italy

March 12-March 19, 2005

I) Exclusive charmless SL decays–Tagged analysis: B0l+ and B+l+–Untagged analysis: B0l+ –Motivations:

•extract Vub (CKM) •Form Factor calculations (QCD)

II) BXs decays–Fully inclusive analysis–Sum of exclusive states analysis–Motivations:

•search for New Physics (NP)•photon spectrum in bs decays is used to determine Heavy Quark parameters mb and

2 (QCD)

All results presented here are preliminary!

Walsh - Moriond QCD 2005 2

Exclusive Bl decays

• |Vub| determines one side of the Unitarity Triangle– Precise measurments of |Vub| and sin2 constrain the U.T.

• Error on |Vub| dominated by theory:– Inclusive analyses – prediction of spectra: theory error ~

10-15% of |Vub|, need Shape Function from BXs

– Exclusive decays – theory must predict form factors – uncertainty hard to quantify

• This talk focus on new results from BaBar on exclusive decays B()l : 2 types of analyses– Tagged analysis, using BD(*)l of “other” B to tag

event reduced BG levels– Untagged analysis, emphasis on neutrino

reconstruction higher statistics

Walsh - Moriond QCD 2005 3

Form Factors Bl

• Calculations:– Light-Cone Sum Rules

• Ball/Zwicky (hep-ph/0406232) quote 10-13% uncertainty at q2=0

• Range of validity: q2 < 14 GeV2

– Lattice QCD• Unquenched calculations

from HPQCD (hep-lat/0408019) and FNAL (hep-lat/0409116) quote 11% uncertainty at high q2

• Valid above ~ 15 GeV2

– ISGW2 • quark model

222

02 3

2 3

( )

24( )F

ub

Gd BV f qp

dq

2

220

2 32 3

( )

24( )F

ub

Gd BV f qp

dq

222 )( ppmq ll

HPQCD’04

Ball’04

FNAL’04

ISGW2

Walsh - Moriond QCD 2005 4

Exclusive Bl decays: tagged analysis

• Use BD(*)l decays of opposite B to “tag” event– consider only products of “recoil” reduce

combinatorial background

• Use doubly-tagged BD(*)l events to check tagging efficiency

• Measure B(B0-l+) in bins of q2

• BF for B+0l+

l

l D(*)

v

v

signal Btag B

Discriminating Variables• B0-l+angle between the B momentum and

the plane defined by the D(*)l and l momenta: cos2B

– <~ 1 for signal events– flat distribution for BG

• B+0l+angle between B and 0l system: cos B-l

– Signal region: −1.1 < cos B-l < 1.0

– BG much broader

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Results: Tagged Analyses

on-peak datasignal MCB lv MCb ¨ ulv MCB0B0 MCB+B− MCoff-peak data

232 million

BB pairs

88 million

BB pairs

B0-l+

B+0l+

40 10)13.025.003.1()( syststatBB

40 10)23.037.080.1()( syststatBB

Branching Fraction Results

in 3 bins of q2

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B()l: untagged analysis

• Reconstruct neutrino from full event + ensure good reconstruction quality

• Fit signal and background in E, mES, and q2

2* ||4/ BES psm

2/* sEE B

22 )( ppq l

neutrino momentum scaled so E=0 improved q2 resolution

q2 resolution

22

21

GeV0.495σ

GeV0.163σ

Walsh - Moriond QCD 2005 7

B()l: Signal ExtractionData

Signal MC

Comb. Sig.

Crossfeed

bcl

qq

Bl

Bl

83 million

BB pairs

BABAR

preliminary

4

0

10)08.018.010.038.1(

)(

FFsyststat

BB

4

0

10)28.053.021.014.2(

)(

FFsyststat

BB

Branching Fraction Results

Walsh - Moriond QCD 2005 8

Form Factor Fits & |Vub|

• The l untagged sample begins to distinguish among FF calculations: ISGW II is disfavored: Prob(2) = 3%

• Other calculations tested are compatible with data

Untaggedl l

BABAR

preliminary

310)65.011.024.014.082.3( ubV

TaggedExtraction of |Vub|

(stat syst FFshapeFFnorm)

uses LQCD-FNAL FF

calculation

Walsh - Moriond QCD 2005 9

BXs Measurements

• Sensitive to New Physics– New heavy particles (Higgs, Susy) can participate in loop process

• Hadronic Effects– Photon Spectrum can be used to measure Heavy Quark

parameters• measure BR and moments as function of min E cut• largest uncertainty in |Vub| from inclusive bul decays due to b

quark motion: can measure it with bs

• Two main experimental techniques:– fully inclusive– sum of exclusive modes

b motion

Emin

Walsh - Moriond QCD 2005 10

Sum of Exclusive Modes

• Sum of 38 modes: Kn, n=1-4, plus modes with and 3 kaon modes

• Kinematic constraints of fully-reconstructed B meson effectively reduces background

• Photon energy measured directly in B rest frame superior resolution

• Primary systematic from missing modes (fragmentation)

bsExperimental Issues

Fully Inclusive

• Reconstruct high-energy photon (1.8-2.8 GeV)

• Suppress huge background with lepton tagging

• Main systematic from subtraction of BB background

• Subtract bd (~4%)

B+B+

B-B-

e or

Xc

Xs

B+B+

B-B-

X

K, Ks,

etc

Walsh - Moriond QCD 2005 11

Fully Inclusive bs

• Continuum Background - – Lepton tagging– Event-shape cuts – Remaining removed

using off-peak data subtraction

• BB Background –– 80% from 0, decays– explicit 0/ vetoes– Remaining subtracted

using MC simulation – with corrections based on 0, control sample

Background-subtracted Event Yield

89 million

BB pairs

Event yield in range 2.0 – 2.7 GeV:– Signal: 992 79stat 53BBsyst

– BB BG: 675 53stat+syst

– Cont. BG: 442 59

Walsh - Moriond QCD 2005 12

Inclusive bsPartial BFs, 1st Moments

E min First Energy Moment: <EBtrue> (GeV)

1.9 2.288 ± 0.025 ± 0.017 ± 0.012

2.0 2.316 ± 0.016 ± 0.010 ± 0.012

2.1 2.355 ± 0.014 ± 0.007 ± 0.010

2.2 2.407 ± 0.012 ± 0.005 ± 0.008

E range Partial BF (×10-4)

1.9 to 2.7 3.67 ± 0.29 ± 0.34 ± 0.29

2.0 to 2.7 3.41 ± 0.27 ± 0.29 ± 0.23

2.1 to 2.7 2.97 ± 0.24 ± 0.25 ± 0.17

2.2 to 2.7 2.42 ± 0.21 ± 0.20 ± 0.13

• First step towards determination of HQ parameters, Shape Function

• Coming soon: 2nd moment measurement• Further interaction with theory

community to extract HQ parameters

( ± stat ± syst ± model )

BABAR

preliminary

Photon Energy Spectrum efficiency corrected

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bsSum of Exclusive States• Reconstruct 38 exclusive states

containing K’s, ’s, ’s, etc.missing fraction is fcn of MXs

• Usual B decay kinematic variables to extract signal: E and mES

• Very good photon energy resolution: note the K* peak

Energy-substituted Mass

Photon Energy Spectrum

89 million

BB pairs

BABAR

preliminary

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bs(Semi-inclusive):BF and Spectrum Moments

Total BF for E>1.6 GeV, use average of Kinetic and Shape Fcn scheme results Good agreement with

inclusive analysis

40.070.640.080.41 10)0.19(3.38)sB(b

( ± stat ± syst ± model )

40.300.28- 10)(3.52)sB(b

World Average (HFAG, August 2004)

Values of moments (For reference,

do not try to read)

Walsh - Moriond QCD 2005 15

OPE theory errors not included

bs(Semi-inclusive):Results on Heavy Quark Parameters

• Heavy Quark parameters related to b-quark mass and its Fermi momentum inside

the B-hadron:

• Results derived for two different theoretical schemes:– Kinetic Scheme (Benson, Bigi, Uraltsev: hep-ph/0410080)– Shape Fcn Scheme (Neubert: hep-ph/0412241)

bB mm

12

BABAR

preliminary

Kinetic

ShapeFcn

Scheme

• Kinetic scheme results can be compared with inclusive SL result from BaBar:

PRL 93, 011803 (2004)

22 GeV05.045.0

GeV07.067.0

( ± stat ± syst ± model )

Walsh - Moriond QCD 2005 16

Summary

• Preliminary results from BaBar on semileptonic and EW penguin decays

• Exclusive analyses of B()l using tagged and untagged samples:– Determination of |Vub|

– BF measurements as function of q2

– Begin to test Form Factor calculations

• The process bsstudied with 2 experimental techniques:– fully inclusive: partial branching fractions and first moment

as a function of Emin towards HQ parameters

– semi-inclusive: BF and moments (1-3)determination of mb and

2

– Will give significant improvement in determination of |Vub| from inclusive SL measurements

Walsh - Moriond QCD 2005 17

Backup slides