Inclusive semileptonic B decays: experimental

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Inclusive semileptonic B decaysexperimental

• Elisabetta Barberio
• University of Melbourne
• FPCP Vancouver April 2006

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Standard Model Consistency Tests
Vub and Vcb provide a test of CP violation in
the Standard Model comparing the measurements on
the (r, h) plane
The width of the green ring need to be reduced
to match sin2b and other measurements The
error on the ring width is dominated by Vub
Goal Accurate determination of Vub
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Semileptonic B decays
tree level, short distance
decay properties depend directly on Vcb,
Vub,mb perturbative regime (asn)
But quarks are bound by soft gluons
non-perturbative (LQCD) long distance
interactions of b quark with light quark
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Inclusive semileptonic decays
Many theorists love inclusive semileptonic decays
Short distance is calculable Long distance
leading order and short distance contribution
are cleanly separated and
probability to hadronnize is 1
To compare Operator Product Expansion predictions
with experiments integration over neutrino and
lepton phase space provides smearing over the
invariant hadronic mass of the final state
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Inclusive semileptonic decays
Vcb vs Vub
Vcb most accurate determination from the
inclusive decays 2 precision limited by
theory error precise Heavy Quarks
parameters, tests of OPE
Vub 7.5 precision shared between experimental
and theoretical errors small rate
and large b?cln background space cuts to
remove b?cln background which introduce
O(1) dependence on non-preturbative b-quark
distribution function
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Vcb from inclusive semileptonic decays
exp. DVcblt1
Gsl described by Heavy Quark Expansion in (1/mb)n
and ask
non perturbative parameters need to be measured
The expansion depend on mb definition
non-perturbative terms are expansion dependent
Theory error was dominated by 1/mb3 terms and
above
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Bc moments in semileptonic decays
Xn are relate to non-perturbative parameters
moments evaluated on the full lepton spectrum or
part of it p? gt pmin in the B rest frame
higher moments are sensitive to 1/mb3 terms ?
reduce theory error on Vcb and HQ parameters
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Inclusive SL decays
Difficulty to go from measured shape to true
shape e.g. QED corrections, accessible phase
space, resolution, background
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moments in semileptonic decays
E? lepton energy spectrum in B?Xc? n (BaBar
Belle CLEO Delphi) MX 2 hadronic mass spectrum
in B?Xc? n (BaBar CDF CLEO Delphi)
Most recent measurements from Belle
mx (GeV)
Pl (GeV)
Pl (GeV)
Plmin 0.7 GeV
Plmin 0.4 GeV
from the moments of these distributions we get
Vcb and HQ parameters
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Parameters Extraction
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Vcb and HQ parameters
Global fit Kinetic scheme expansion
(hep-ph/0507253) dVcb _at_ 2 mb lt 1, mc _at_
5 U(1S) expansion scheme has similar results
used measurements
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Vub inclusive determination
B? Xuln rate tree level from OPE ? corrected for
perturbative as and non-perturbative 1/mb terms
In principle main uncertainty from mb5
BUT.. Br(B?Xuln)/Br(B?Xcln) 1/50
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Shape Function
Limited phase space to reduce the B ? Xcln
background OPE doesnt work everywhere in the
phase space ? non-perturbative Shape Function
F(K) to extrapolate to the full phase space
Detailed shape not constrained, in particular
the low tail
Mean and r.m.s. are known
Shape Function need to be determined from
experimental data
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Inclusive B ? Xuln
mu ltlt mc ? exploits different kinematics
Signal events have smaller MX and P ? Larger El
and q2
Not to scale!
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Lepton Endpoint
BABAR PRD 7312006Belle PLB 62128CLEO PRL
88231803
First measurement from CLEO Elgt2.3 GeV
BaBar Elgt2.0 GeV Belle Elgt 1.9 GeV Crucial
accurate subtraction of background is crucial!
S/B 1/10 eff 40
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Measuring mX q2 P
BABAR hep-ex/0507017Belle PRL 95241801
Reconstruct all decay products to measure MX ,q2
or P
fully-reconstructed B meson flavor and momentum
known lepton in the recoil-B mmiss consistent
with a neutrino lepton charge consistent with B
flavor left-over particles belong to X
equal mB on both sides mmiss 0
S/B 2 Eff 0.1
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Measuring Partial Branching Fraction
P BLNP PRL93221802
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Turning DB into Vub
SSFs
Inclusiveb ? ulv
El
HFAG main results HQ parameters form b ? Xcln
and b ? Xsg hep-ph/0507253
Vub
q2
mX
duality
WA
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Dealing with Shape Function
easy to fit shape function
Better resolution ? K peak (more difficult for
SF)
Eg (GeV)
Eg (GeV)
Solution ? use directly the g spectrum
theory
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Inclusive Vub BLNP framework
Vub world average as of Winter 06
Inputs mb(SF) 4.60 ? 0.04 GeV mp2(SF) 0.20
? 0.04 GeV2
VubBLNP(4.45 ? 0.20 ? 0.26) 10-3
dVub ? 7.3
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Theory Errors

• Quark-hadron duality is not considered (cut
  dependent)
• b ?cln and b ? sg data fit well HQ predictions
• Weak annihilation ? ? 1.9 error
• Expected to be lt2 of the total rate
• Gw.a./G(b ? u) lt 7.4 from CLEO
• HQ parameters ? ? 4.1 mainly mb kinematics cuts
  depend on mb,!
• Sub-leading shape function ? ? 3.8 dominated by
  the lepton endpoint measurements

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Inclusive Vub DGE framework
Dressed Gluon Exponentiation (DGE) on-shell
b-quark calculation converted into hadronic
variables used as approximation to the meson
decay spectrum
Still digesting the method
VubDGE (4.41 ? 0.20 ? 0.20) 10-3
DGE theory ? ?2.9 matching scheme method and
scale mb(MS) ? ? 1.3 on event fraction
mb(MS)4.20?0.04 GeV as ? ?
1.0 on event fraction total GSL ? ? 3.0
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Vub without Shape Function
Babar
Based on Leibovich, Low, Rothstein, PLB
48686 First proposal by Neubert
Weight function
Babar
Babar
mxcut
OPE mxlt2.50 GeV
LLR mxlt1.67 GeV
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Vub inclusive vs exclusive
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Vub CKM consistency
Most probable value of Vub from measurements of
other CKM parameters Standard Model predictions
with Dms measurement (thank to Pierini)
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Conclusions
b? cln Vcb 2 error dominated by theory, mb _at_1
(kinetic and U(1S) schemes), mc _at_5 (kinetic
scheme) but how well do we know the B? Xcln
spectrum? b? uln Vub 7.4 error shared
between theoretical and experimental inclusive
vs exclusive less than 1.4 s difference,
depending on the inclusive extracting method We
have now different methods to extract Vub Vub
_at_ 5 possible? Improve knowledge of B? Xcln, B?
Xuln and more work on the theoretical error
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Inclusive Vub comparisons
HQ parameters from cln and sg
HQ parameters from sg only
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Mx unfolded spectrum for B ? Xc l n
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photon energy spectrum
Eg photon energy spectrum in B?sg (BaBar
Belle CLEO Delphi)
photon energy spectrum in B? Xsg not sensitive to
new physics and give information on B structure
CLEO