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DESCRIPTIONRon Poling WIN03 October 7, 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 |V cb | and |V ub | in semileptonic B decays. –Detailed studies to guide interpretation and help clear the “fog” of nonperturbative effects. Challenging experimentally and theoretically. V cb or V ub
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.
Vcb or Vub
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B Semileptonic Branching Fraction
• CLEO II: 10 fb-1 at (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 (BXe) from secondary (BD Ye).
• Refined electron ID, background and efficiency determinations.
– Maximize understanding and minimize momentum dependence.
CLEO - Preliminary
Preliminary: B(BXe)=(10.88 0.08 0.33)%
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BSL – Still small-ish, but consistent
• Good agreement among different techniques, experiments.
• Measurements at (4S) have come up and LEP Z0 average has come down.– Most recent LEP fit
result is (10.590.22)%
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The 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.
Vcb or Vub
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HQET+OPE• Expresses observables of inclusive b decay as expansions in
inverse powers of MB (Voloshin +Shifman, …).• One parameter at order QCD/MB:
~ MB – mb is the energy of light-quark and gluon degrees of freedom in the B meson.
• Two parameters at order 2QCD/M2
1 – negative of the average b-quark momentum squared. 2 – energy of the hyperfine interaction of the b spin with the light degrees of
freedom (from B*-B splitting: 2 = (0.128 0.010) GeV).• Six more parameters at order 3
(Gremm and Kapustin):
1, 2, T1, T2, T3, T4 (not all independent).• Meaning of parameters depends on choices: order of perturbative
(0(s/)2 ) and nonperturbative (1/M3B) expansions and mass scheme.
Consistency required. |Vcb| is what counts!
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MOMENTS, INC. – CLEO Branch
• BXs Photon-Energy Moments• BXl Lepton-Energy Moments• BXl 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.
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• Use all available tools!– Traditional shape variables.– Pseudo-reconstruction: demand
consistency with BK(n)– Use neural net to compute signal
probability and measure spectrum of “weights.”
– Subtract continuum with below-(4S) data.
– Subtract backgrounds with Monte Carlo, informed by data wherever possible.
Photon-energy spectrum at (4S)
Continuum must be suppressed.
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Measuring BXs• 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 (4S)
– <E> gives nearly direct access to .
Next, measure the moments of the E spectrum by fitting to model of Ali-Greub or HQT calculation of Kagan-Neubert:
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Hadronic Mass Moments in BXcl
• Select events with leptons with– 1.5 < pl < 2.5 GeV/c
• “ reconstruction” to measure p.• Calculate approximate hadronic
recoil mass using l (take advantage of pB small):
• Construct continuum-subtracted spectrum and fit to mixture:– BDl (CLEO FF’s)– BD*l (CLEO FF’s)– High-mass, nonresonant by models
• Use fit components to compute moments:
= 0.2510.023 0.062 GeV2
= 0.6390.056 0.178 GeV2
PRL 88, 251808 (2001)
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Interpreting the Moments
• First moments E and MX2-
MD2 fitted to extract and 1.
• Combined solution is = 0.350.0700.10 GeV1 = -0.2360.0710.078 GeV2
• Precise meaning of parameters is scheme- and order-dependent; these are to order 1/MB
3, order 0s
2 in MS scheme.
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Extracting |Vcb| from (BXcl)
• Ingredients: (BXcl) = (10.80.3)% (CLEO) B0 and B (PDG), f+/ f00 (CLEO) SL = (0.44 0.02) 10-10 MeV
• Result:|Vcb| = 0.041 0.0005 0.0007 0.0009
Overall precision: ~3% + quark-hadron duality.
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|Vcb| from BD*l d/dw
PRL 88, 251808 (2001)
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New and Improved Measurement of the Hadronic Mass Moments in BXcl
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).
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Fit Projections• Selection criteria:
– Cuts to enhance reconstruction– Continuum suppression– Efficiency ~2% for BXcl
• Sample to fit: 122K events• Components of fit:
– BDl– BD*l– BD**l ISGW2
– B(Xc)NRl Goity/Roberts
– BXul ISGW2+NR– Secondaries CLEO MC– Fake Leptons, Continuum fixed
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Fits Mode-by-Mode BRs
(Fraction above pl cut, moment value for that cut.)
Moment Value for BXcl
• 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
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BXcl Energy Moments PRD 67, 072001 (2003)
Pending…El moments down to 0.6 GeV
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Improved Inclusive Measurement of |Vub|
• End-point technique:– Isolate BXul by looking above
(and just below) the BXcl kinematic limit.
– Used for bu discovery (CLEO, ARGUS) and CLEO 93: |Vub|/|Vcb|= 0.080.02
Significant model dependence.
• Can now do better:– Better knowledge of BXcl.
– BXs helps determine fraction of spectrum in end point.
BXs spectrum shape function fu
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2.0 < pl <2.6 GeV/c Suppress continuum with neural
net (energy flow w.r.t. lepton). Less q2- and M(Xu)-dependent.
Estimate BXcl by fitting inclusive spectrum. Components reflect state-of-the-art on form factors, b.r.’s, etc.
Trade-off: BXcl uncertainty vs. spectral-fraction uncertainty.
PRL 88, 231803 (2002)
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• Hoang, Ligeti, Manohar; Uraltsev:
• Determine from B Xs shape-function fits (Kagan-Neubert).
In preparation: Paper with details of fits for shape-function parameters and fu values for phase-space regions other than just end point.
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Branching Fractions and q2 Dependenceof Bl and B()l
and Extraction of |Vub|
• Exclusive reconstruction of B(///)l through neutrino “detection.”
• Near hermeticity of CLEO II Neutrino=“What’s missing”
hep-ex/0304019 to be published
Signal defined by…
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Bl (pl > 1.0 GeV/c) Bl (pl > 1.5 GeV/c)
• CLEO II 10 fb-1
• Event selection to enhance reconstruction, suppress continuum
• Fit Mml and E in three bins in q2 to find branching fractions
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• Extracting |Vub|
– Fit d/dq2
– Discriminates among FFs• Bl
– FF dependence is small– Disfavors ISGW2
• Bl– Larger FF
dependencegreater model uncertainty in |Vub|
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Ron Poling WIN03 October 7, 2003 26
Comparisons and CKM Impact
90% c. l. contours
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• 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 bul 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 Prospects