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Semileptonic B physics at CLEO
Ron PolingUniversity of Minnesota
CLEO CollaborationCLEO-c Collaboration
Ron Poling WIN03 October 7, 2003 2
CESR and CLEO: 23 years of B Physics
Three generations of detectors, ~170 Ph.D.’s, ~360 papers
Ron Poling WIN03 October 7, 2003 3
The Global Program of CKM Tests
• Goal: redundant determinations of sides and angles of the Unitarity Triangle(s)
• CLEO’s Role:– Measure UT sides through |Vcb|
and |Vub| in semileptonic B decays.– Detailed studies to guide
interpretation and help clear the “fog” of nonperturbative effects.
• Challenging experimentally and theoretically.
q c or uq
e, µ, ν
τVcb or Vub
Ron Poling WIN03 October 7, 2003 4
B Semileptonic Branching Fraction
• CLEO II: 10 fb-1 at ϒ(4S)– Mature, well-understood detector,
data, Monte Carlo, generators, etc.• Lepton-Tagged Analysis
– ptag>1.4 GeV/c plus accompanying electron with pe>0.6 GeV/c.
– Charge, angular correlations to separate primary (B→Xeν) from secondary (B→D →Yeν).
• Refined electron ID, background and efficiency determinations.– Maximize understanding and
minimize momentum dependence.
CLEO - Preliminary
Preliminary: B(B→Xeν)=(10.88 ± 0.08 ± 0.33)%
Ron Poling WIN03 October 7, 2003 5
BSL – Still small-ish, but consistent
• Good agreement among different techniques, experiments.
• Measurements at ϒ(4S) have come up and LEP Z0 average has come down.– Most recent LEP fit
result is (10.59±0.22)%
Ron Poling WIN03 October 7, 2003 6
The Reality of Semileptonic B DecaysThe Reality of Semileptonic B Decays
• We idealize them as…
• The real picture is…
• View of b decay obscured by…– Hadronic effects describable by
both perturbative and nonperturbative QCD.
– Uncertainty about our assumption of quark-hadron duality.
• Available tools include Heavy Quark Effective Theory and Lattice QCD. Must be validated by experiment.
q c or uq
e, µ, ν
τVcb or Vub
Ron Poling WIN03 October 7, 2003 7
• Expresses observables of inclusive b decay as expansions in inverse powers of MB (Voloshin +Shifman, …).
• One parameter at order ΛQCD/MB:– Λ~ MB – mb is the energy of light-quark and gluon degrees of freedom
in the B meson.• Two parameters at order Λ2
– λ1 – negative of the average b-quark momentum squared.– λ2 – energy of the hyperfine interaction of the b spin with the light
degrees of freedom (from B*-B splitting: λ2 = (0.128 ± 0.010) GeV).• Six more parameters at order Λ3
QCD/M3B (Gremm and Kapustin):
– ρ1, ρ2, T1, T2, T3, T4 (not all independent).• Meaning of parameters depends on choices: order of perturbative
(β0(αs/π)2 ) and nonperturbative (1/M3B) expansions and mass
scheme. Consistency required. |Vcb| is what counts!
Ron Poling WIN03 October 7, 2003 8
MOMENTS, INC. – CLEO Branch
• B→Xsγ Photon-Energy Moments• B→Xlν Lepton-Energy Moments• B→Xlν Hadronic Recoil Mass Moments
First and second moments, different lepton-energy ranges…
Lots of complementary information.
Data from different processes will tell us if this approach provides a coherent picture of inclusive B decays.
Ron Poling WIN03 October 7, 2003 9
• Use all available tools!– Traditional shape variables.– Pseudo-reconstruction: demand
consistency with B→K(n)πγ– Use neural net to compute signal
probability and measure spectrum of “weights.”
– Subtract continuum with below-ϒ(4S) data.
– Subtract backgrounds with Monte Carlo, informed by data wherever possible.
Photon-energy spectrum at ϒ(4S)
⇒Continuum must be suppressed.
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Measuring B→Xsγ• CLEO II – 10 fb-1
• PRL 87, 251807 (2001)• Hard measurement, simple
interpretation:– Almost two-body, with
broadening by Fermi motion, gluon bremsstrahlung, boost of B’s at ϒ(4S)
– <Eγ> gives nearly direct access to .
Next, measure the moments of the Eγ spectrum by fitting to model of Ali-Greub or HQT calculation of Kagan-Neubert:
Ron Poling WIN03 October 7, 2003 11
Hadronic Mass Moments in B→Xclν
• Select events with leptons with– 1.5 < pl < 2.5 GeV/c
• “ν reconstruction” to measure pν.• Calculate approximate hadronic
recoil mass using lν (take advantage of pB small):
• Construct continuum-subtracted spectrum and fit to mixture:– B→Dlν (CLEO FF’s)– B→D*lν (CLEO FF’s)– High-mass, nonresonant by
models (ISGW2, Goity/Roberts)
• Use fit components to compute moments:
= 0.251±0.023 ±0.062 GeV2
= 0.639±0.056 ±0.178 GeV2
PRL 88, 251808 (2001)
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Interpreting the Moments
• First moments <Eγ> and <MX
2- MD2 > fitted to extract
Λ and λ1.• Combined solution is
Λ = 0.35±0.070±0.10 GeV λ1 = -0.236±0.071±0.078 GeV2
• Precise meaning of parameters is scheme- and order-dependent; these are to order 1/MB
3, order β0αs2 in MS
Ron Poling WIN03 October 7, 2003 13
Extracting |Vcb| from B(B→Xclν)
• Ingredients:B(B→Xclν) = (10.8±0.3)% (CLEO)τB0 and τB± (PDG), f+−/ f00 (CLEO)
⇒ ΓSL = (0.44 ± 0.02) × 10-10 MeV
• Result:|Vcb| = 0.041 ± 0.0005 ± 0.0007 ± 0.0009
Overall precision: ~3% + quark-hadron duality.
Ron Poling WIN03 October 7, 2003 14
|Vcb| from B→D*lν dΓ/dw
PRL 88, 251808 (2001)
Ron Poling WIN03 October 7, 2003 15
New and Improved Measurement of theHadronic Mass Moments in B→Xclν
hep-ex/0307081 - Contributed to Lepton-Photon 2003
• Compute recoiling hadronic mass from charged lepton and neutrino kinematics - neutrino “detection.”
• Near hermeticity of CLEO II ⇒Neutrino=“What’s missing”
Fit 3-dimensional differential decay rate, extract hadronic mass squared as a function of lepton-energy cut (pl > 1 GeV/c).
Ron Poling WIN03 October 7, 2003 16
Fit Projections• Selection criteria:
– Cuts to enhance ν reconstruction– Continuum suppression– Efficiency ~2% for B→Xclν
• Sample to fit: 122K events• Components of fit:
– B→Dlν– B→D*lν– B→D**lν ISGW2
– B→(Xc)NRlν Goity/Roberts– B→Xulν ISGW2+NR– Secondaries CLEO MC– Fake Leptons, Continuum fixed
Ron Poling WIN03 October 7, 2003 17
Fits →Mode-by-Mode BRs
(Fraction above pl cut, moment value for that cut.)
⇓Moment Value for B→Xclν
• Consistent with previous CLEO measurements, BaBar summer ’03
• Interpretation continues
DELPHI: energy and hadronic mass moments for full lepton-energy spectrum. hep-ph/0210319 PRELIMINARY
Ron Poling WIN03 October 7, 2003 18
B→Xclν Energy Moments PRD 67, 072001 (2003)
Pending…El moments down to 0.6 GeV
Ron Poling WIN03 October 7, 2003 19
Improved Inclusive Measurement of |Vub|
• End-point technique:– Isolate B→Xulν by looking above
(and just below) the B→Xclνkinematic limit.
– Used for b→u discovery (CLEO, ARGUS) and CLEO 93: |Vub|/|Vcb|= 0.08±0.02Significant model dependence.
• Can now do better:– Better knowledge of B→Xclν.– B→Xsγ helps determine fraction
of spectrum in end point. B→Xsγ spectrum ⇒ shape function ⇒ fu
Ron Poling WIN03 October 7, 2003 20
2.0 < pl <2.6 GeV/cSuppress continuum with neural net (energy flow w.r.t. lepton). Less q2- and M(Xu)-dependent.Estimate B→Xclν by fitting inclusive spectrum. Components reflect state-of-the-art on form factors, b.r.’s, etc.Trade-off: B→Xclν uncertainty vs. spectral-fraction uncertainty.
PRL 88, 231803 (2002)
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• Hoang, Ligeti, Manohar; Uraltsev:
• Determine from B→ Xsγ shape-function fits (Kagan-Neubert).
In preparation: Paper with details of fits for shape-function parameters and fuvalues for phase-space regions other than just end point.
Ron Poling WIN03 October 7, 2003 22
Branching Fractions and q2 Dependenceof B→πlν and B→ρ(ω)l ν
and Extraction of |Vub|
• Exclusive reconstruction of B→(π/η/ρ/ω)l ν through neutrino “detection.”
• Near hermeticity of CLEO II ⇒ Neutrino=“What’s missing”
hep-ex/0304019 to be published
Signal defined by…
Ron Poling WIN03 October 7, 2003 23
B→πlν (pl > 1.0 GeV/c) B→ρlν (pl > 1.5 GeV/c)
• CLEO II 10 fb-1
• Event selection to enhance ν reconstruction, suppress continuum
• Fit Mmlν and ∆E in three bins in q2 to find branching fractions
Ron Poling WIN03 October 7, 2003 24
• Extracting |Vub|
– Fit dΓ/dq2
– Discriminates among FFs• B→πlν
– FF dependence is small– Disfavors ISGW2
• B→ρlν– Larger FF
dependence⇒greater model uncertainty in |Vub|
Ron Poling WIN03 October 7, 2003 25
Ron Poling WIN03 October 7, 2003 26
Comparisons and CKM Impact
0 2 4 6
CLEO lepton endpoint
BELLE D*�ν (prelim)
BELLE M & q (prelim)
Mean with 25% error
V x 10ub-3
-1 -0.5 0 0.5 1 1.5 2
∆ms & ∆md
f i t t e rpackage
90% c. l. contours
Ron Poling WIN03 October 7, 2003 27
• CLEO is still contributing on |Vub| and |Vcb|.– Sample smaller than B factories, but well understood with
mature tools.– We’re all limited by theoretical uncertainties.
• Continuing and forthcoming CLEO CKM-related measurements:– Completion of moment measurements, coordinated fits of all
available inputs.– Inclusive b→ulν for all CLEO II and CLEO III via
multidimensional fit and bigger phase-space acceptance.• CESR-c/CLEO-c will have significant impact on CKM.
See the upcoming of Karl Ecklund.
Perspectives and ProspectsPerspectives and Prospects