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
method S/B ProsCons Vub(x10-3)
Electron spectrum endpoint Eegt2.0GeV Total rate using DeFazio-Neubert 0.05?0.2 High statistics Duality valid for tight Ee cuts? Bkg subtraction
Ee vs q2 and neutrino reconstruction Eegt2.0GeV and shlt3.5 GeV2/c4 Total rate using DeFazio-Neubert 0.5 High statistics Lower syst. on shape functions Bkg subtraction
mX analysis (1-D) mXlt1.55 GeV/c2 Total rate using DeFazio-Neubert 1.7 Low background High resolution Low statistics Shape func. syst.
mX vs q2 analysis mXlt1.7 GeV/c2 and q2 gt8.0 GeV2/c4 Vub using Bauer et al. 2 Low background Very small syst. on SF param. Small statistics
Total rate using Form Factors calc. 1?20 Very small bkg no cut on kinem Small statistics
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)

Method ?B 104 Vub (BLNP) SF params from b?cl? Vub (BLNP) (Belle SF) Vub ICHEP (DFN, Belle SF)
Endpoint 5.310.59 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 4.460.93 3.89 0.40 0.45 0.21 (10.3 11.5 5.4) 4.53 4.99 0.48 0.29 ( 9.6 5.8)
q2-mx 8.962.04 4.45 0.49 0.40 0.22 (11.1 9.0 4.9) 5.00 5.18 0.57 0.34 ( 11.0 6.5)
Average 4.07 0.51 4.61 0.46
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)