Stato di Vub e Vcb

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Stato di Vub e Vcb

• Concezio Bozzi
• INFN Ferrara
• Babar Italia, Trieste 14 Aprile 2005

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Sommario

• Decadimenti semileptonici inclusivi
• con charm (Vcb)
• senza charm (Vub)
• Decadimenti semileptonici esclusivi
• pln, rln (nuovi risultati, MoriondCKM05)
• Dln
• NB ho attinto a piene mani da materiale
  presentato (da altri ma anche da me!) a CKM2005

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Misure inclusive
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Inclusive Decays the Big Picture
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Semileptonic B Decays HQE
free-quark rate
m 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
(asj , askb0)

• contains b- and c-quark masses, mb and mc
• mp2 related to kinetic energy of b-quark
• mG2 related to chromomagnetic operator B / B
  mass splitting
• Darwin term (?D3) and spin-orbit interaction
  (?LS3) enter at 1/mb3

No 1/mb term!
Several HQE schemes exist ops and coeffs are
scheme dependent
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Inclusive b?cl?

• 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

Gambino Uraltsev (hep-ph/0401063, 0403166)
Lepton energy spectrum
Mass of hadronic system
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Fit Results
BABAR PRL 93011803
? used, ? unusedin the nominal fit
mX moments
BABAR
El moments
Red line OPE fitYellow band theory errors
c 2/ndf 20/15
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Fit Results
BABAR PRL 93011803
2 accuracy!
precision on Vcb 2
Uncalculatedcorrections to G
precision on mb 1.5

• kinetic mass scheme with µ1 GeV
• Fitted values consistent with external knowledge
• c 2/ndf 20/15

• Impressive agreement between data and theory
• identical results obtained in another renorm.
  scheme Bauer, Ligeti, Luke, Manohar, Trott in
  hep-ph/0408002

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Inclusive Vcb status

• BaBar result compared with previous measurements
• Agrees with value coming from exclusive B?D l ?
  decays (from HFAG)

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Inclusive b?u

• Limiting factor in CKM precision tests known
  much less well than Vcb
• CKM suppressed therefore harder to measure
• Challenge for experiment and theory

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Starting point HQE

• Just like b?cl?, and with similar accuracy
• until limited exptl acceptance is considered
• Poor convergence of OPE in region where b?cl?
  decays are kinematically forbidden
• Non-perturbative Shape Function must be used to
  calculate partial rates

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Theory input

• Reference (ICHEP04, HFAG) results based on triple
  differential decay rate (Ee, mX, q2) computed to
  O(as, mb-2) over the entire phase space by de
  Fazio and Neubert (DFN, JHEP 0617 (1999))
• Use as input the shape function parameters
  determined by a fit (hep-ex/0407052) to the Belle
  b?sg spectrum
• ? 0.66 GeV, ?1 -0.40 GeV2 covariance
• d? dmb 80 MeV

Acceptance inb ? ulv
Eg spectrum inb ? sg
f(k)

• 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.

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Inclusive Vub measurements with BaBar
Untagged
4.40 0.24exp 0.35theo
Untagged
4.99 0.48exp 0.29theo
Breco Tags
5.22 0.43exp 0.33theo
Breco Tags
5.18 0.57exp 0.34theo
Current Vub errors 10-15 Total experimental
syst _at_250-500 ifb 3-6
Partial Tags
exclusive
Breco Tags
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Vub measurements
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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?sg
• hep-ex/0407052
• BaBar b?cln moments (hadronic and leptonic)
• hep-ex/0404017
• Proper translation into shape function scheme of
  BLNP
• hep-ph/0412241

Courtesy of Henning Flächer
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Results with BLNP and BaBar b?cln moments

• Using mb 4.630.08 GeV and µp2 0.150.07
  GeV2 (SF scheme) with correlation coefficient
  -0.4. Errors are expt SF theory expt
  (SFtheory)

b?cln moments significant change in inclusive
Vub values BLNP increased sensitivity to SF
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Misure di Vub esclusive
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Exclusive B ? Xuln Decays
Xu p, p0, r, r0, w, h, h, a00, a0 low bkg,
low stat. 27p, (ICHEP04)
Breco Tags
p
Balance between efficiency and purity
3 new pln results
Semilep.Tags
Y(4S)
n
l-
High statistics, high hackground (b ? cln)
Untagged

• ? Goal Measure Branching Fractions and Vub
• ? Need FF predictions to describe QCD effects
• New unquenched LQCD calculations (HPQCD04,
  FNAL04)
• Try to measure q2 dependence of FF with
  data

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Semileptonic Tag Analyses

• Reconstruct B ? D()ln and study semileptonic
  recoil

• use both D and D tags ? sizable BF
• Tagging efficiency measured with Double Tags
  (two D()ln)

D()ln decays
Correct sl. decay ? cosqBY lt 1 ( tag side
cosqBY, signal side cosqB,pl )
cos2fB lt 1 for signal, bkg flat
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p0ln with SL Tag Signal Extraction

• Cut-and-count analysis in cosqB,pl and mD
• Signal region -1.1 lt cosqBpl lt 1.0
• Subtract mD sidebands
  ? remove cominatoric
  background
• Subtract other background using MC
  normalized in -10 lt cosqBpl lt -1.5

82 fb-1
45 p0
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pln with SL Tag Signal Extraction
Extract signal yields by binned c2 fit to cos2fB
in 3 bins of q2 Fit parameters signal and
background normalizations
14 p
21 p
26 p
211 fb-1
30 rln X-feed
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pln with SL Tag Branching Fractions and q2

• SL tag analyses statistically limited.
• Yields not yet large enough to discriminate
  between FF models.

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Untagged B ? pln and B ? rln

• Neutrino Reconstruction Reconstruct n from full
  event
• 
  ensure good
  reco. quality

• Cut on missing mass M2miss / 2Emiss lt 0.4 GeV

• Harsh suppression of b ? cln bkg (kinem.
  cuts, mainly for rln)
• ee- ? qq
  bkg (topological cuts)

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

• Fit all 4 signal modes simultaneously (p, p0,
  r, r0)
• Use isospin relations to reduce number of signal
  parameters
• G (B0 ? p-ln)
  2 G (B ? p0ln)
• G (B0 ? r-ln)
  2 G (B ? r0ln)

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Untagged pln Fitted DE and mES
76 fb-1
427 p, 147 p0
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Untagged pln Fitted DE and mES
76 fb-1
101 r, 104 r0
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Measured q2 Distributions and Form Factors
pln
rln

• Recent LQCD and LCSR calculations agree well with
  data
• ISGW2 shows marginal agreement for pln
• Errors for rln still too large to study 3 form
  factors.

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Systematic Uncertainties (Untagged)

• Better statistical precision than previous
  measurements
• Syst. error dominated by n reconstruction. Will
  decrease with improved track/neutral
  reconstruction.
• Results less dependent on theoretical predictions
  (own FF measurement)

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Overview Branching Fraction Measurements
pln
rln
Testing isospin symmetry Measure pln, p0ln
separately (untagged)
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Extraction of Vub

• Measurement in bins of q2 allows extraction of
  Vub for various q2 regimes and FF calculations
  
• LCSR q2 lt15 GeV2, LQCD q2 gt 15 GeV2
  
  or extrapolation to whole q2 range

Quote LQCD2 as representative
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Misure di Vcb esclusive
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Ultimate solution combined measurement of form
factors and Vcb! (work in progress in Trieste)
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Other ideas?

• D0ln (little/undermanned efforts)
• Yet another measurement of Dln
• D partial reconstruction
• On the recoil of a fully reconstructed hadronic
  decay

M. Andreotti PhD thesis
Run1-4
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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?cl? ? b?sg ? b?ul?
• 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 (Dln) per limitare incertezze
  teoriche e per risolvere laccordo marginale tra
  le misure esistenti (Dln)