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Stato di Vub e Vcb

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Title: Stato di Vub e Vcb Author: Concezio Bozzi Last modified by: Concezio Bozzi Created Date: 4/13/2005 8:33:35 PM Document presentation format – PowerPoint PPT presentation

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Title: Stato di Vub e Vcb


1
Stato di Vub e Vcb
  • Concezio Bozzi
  • INFN Ferrara
  • Babar Italia, Trieste 14 Aprile 2005

2
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

3
Misure inclusive
4
Inclusive Decays the Big Picture
5
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
6
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
7
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
8
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

9
Inclusive Vcb status
  • BaBar result compared with previous measurements
  • Agrees with value coming from exclusive B?D l ?
    decays (from HFAG)

10
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

11
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

12
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.

13
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
14
Vub measurements
15
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
16
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
17
Misure di Vub esclusive
18
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

19
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
20
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
21
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
22
pln with SL Tag Branching Fractions and q2
  • SL tag analyses statistically limited.
  • Yields not yet large enough to discriminate
    between FF models.

23
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)

24
Untagged pln Fitted DE and mES
76 fb-1
427 p, 147 p0
25
Untagged pln Fitted DE and mES
76 fb-1
101 r, 104 r0
26
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.

27
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)

28
Overview Branching Fraction Measurements
pln
rln
Testing isospin symmetry Measure pln, p0ln
separately (untagged)
29
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
30
Misure di Vcb esclusive
31
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36
Ultimate solution combined measurement of form
factors and Vcb! (work in progress in Trieste)
37
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38
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
39
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)
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