Semileptonic and EW Penguin Decay Results from BaBar

1
Semileptonic and EW Penguin Decay Results from
BaBar

• I) Exclusive charmless SL decays
• Tagged analysis B0?p-ln and B?p0ln
• Untagged analysis B0?p-(r-)ln
• Motivations
• extract Vub (CKM)
• Form Factor calculations (QCD)
• II) B?Xsg decays
• Fully inclusive analysis
• Sum of exclusive states analysis
• Motivations
• search for New Physics (NP)
• photon spectrum in b?sg decays is used to
  determine Heavy Quark parameters mb and mp2 (QCD)

• John J. Walsh
• INFN-Pisa
• BaBar Collaboration

All results presented here are preliminary!
XXXXth Rencontres de Moriond QCD and Hadronic
Interactions La Thuile, Italy March 12-March 19,
2005
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Exclusive B?p(r)ln decays

• Vub determines one side of the Unitarity
  Triangle
• Precise measurments of Vub and sin2b 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 B?Xsg
• Exclusive decays theory must predict form
  factors uncertainty hard to quantify

• This talk ? focus on new results from BaBar on
  exclusive decays B?p(r)ln 2 types of analyses
• Tagged analysis, using B?D()ln of other B to
  tag event ? reduced BG levels
• Untagged analysis, emphasis on neutrino
  reconstruction ? higher statistics

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Form Factors B?pln

• Calculations
• Light-Cone Sum Rules
• Ball/Zwicky (hep-ph/0406232) quote 10-13
  uncertainty at q20
• Range of validity q2 lt 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

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Exclusive B?pln decays tagged analysis

• Use B?D()ln decays of opposite B to tag event
• consider only products of recoil ? reduce
  combinatorial background
• Use doubly-tagged B?D()ln events to check
  tagging efficiency
• Measure DB(B0?p-ln) in bins of q2
• BF for B?p0ln

• Discriminating Variables
• B0?p-ln angle between the B momentum and the
  plane defined by the D()l and pl momenta cos2fB
  
• lt 1 for signal events
• flat distribution for BG
• B?p0ln angle between B and p0l system cos
  ?B-pl
• Signal region -1.1 lt cos ?B-pl lt 1.0
• BG much broader

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Results Tagged Analyses
232 million BB pairs
B0?p-ln
on-peak datasignal MCB ?rlv MCb ? ulv MCB0B0
MCBB- MCoff-peak data
88 million BB pairs
B?p0ln
Branching Fraction Results
in 3 bins of q2
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B?p(r)ln untagged analysis

• Reconstruct neutrino from full event ensure
  good reconstruction quality
• Fit signal and background in DE,
• mES, and q2

q2 resolution
neutrino momentum scaled so DE0 ? improved q2
resolution
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B?p(r)ln Signal Extraction
BABAR preliminary
B?pln
B?rln
Branching Fraction Results
83 million BB pairs
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Form Factor Fits Vub
Untagged
pln
rln

• The pln untagged sample begins to distinguish
  among FF calculations ISGW II is disfavored
  Prob(c2) 3
• Other calculations tested are compatible with
  data

Tagged
Extraction of Vub
(stat ? syst ? FFshape?FFnorm)
BABAR preliminary
uses LQCD-FNAL FF calculation
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B?Xsg Measurements
b motion

• 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 Eg cut
• largest uncertainty in Vub from inclusive b?uln
  decays due to b quark motion can measure it with
  b?sg
• Two main experimental techniques
• fully inclusive
• sum of exclusive modes

Emin
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b?sg Experimental Issues

• Sum of Exclusive Modes
• Sum of 38 modes Knp, n1-4, plus modes with h
  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)

• 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 b?dg (4)

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Fully Inclusive b?sg
89 million BB pairs
Background-subtracted Event Yield

• Continuum Background -
• Lepton tagging
• Event-shape cuts
• Remaining removed using off-peak data subtraction
• BB Background
• 80 from p0, h decays
• explicit p0/h vetoes
• Remaining subtracted using MC simulation with
  corrections based on p0, h control sample

• Event yield in range 2.0 2.7 GeV
• Signal 992 ? 79stat ? 53BBsyst
• BB BG 675 ? 53statsyst
• Cont. BG 442 ? 59

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Inclusive b?sg Partial BFs, 1st Moments
Photon Energy Spectrum efficiency corrected
( stat syst model )

• First step towards determination of HQ
  parameters, Shape Function
• Coming soon 2nd moment measurement
• Further interaction with theory community to
  extract HQ parameters

BABAR preliminary
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b?sg Sum of Exclusive States
BABAR preliminary

• Reconstruct 38 exclusive states containing Ks,
  ps, hs, etc.?missing fraction is fcn of MXs
• Usual B decay kinematic variables to extract
  signal DE and mES
• Very good photon energy resolution note the Kg
  peak

Energy-substituted Mass
89 million BB pairs
Photon Energy Spectrum
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b?sg (Semi-inclusive) BF and Spectrum Moments

• Total BF for Eggt1.6 GeV, use average of Kinetic
  and Shape Fcn scheme results

Good agreement with inclusive analysis
Values of moments ? (For reference, do not try to
read)
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b?sg (Semi-inclusive) Results on Heavy Quark
Parameters
BABAR preliminary

• 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)

OPE theory errors not included
( stat syst model )
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Summary

• Preliminary results from BaBar on semileptonic
  and EW penguin decays
• Exclusive analyses of B?p(r)ln using tagged and
  untagged samples
• Determination of Vub
• BF measurements as function of q2
• Begin to test Form Factor calculations
• The process b?sg studied 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 mp2
• Will give significant improvement in
  determination of Vub from inclusive SL
  measurements

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Backup slides