Semileptonic Charm Decays and QCD

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Semileptonic Charm Decays and QCD
Doris Y. Kim, University of Illinois
Urbana-Champaign

• Content
• Part I Theories of Charm Semileptonic decays
• Part II q2 dependence in Pseudo-scalar l n
  decays.
• Part III Vector l n decays.
• D ? K0 m n analysis (not so simple!)
• Form factors of Ds ? f m n
• Part V Future of Semileptonic decays.

ISMD Sonoma July 27, 2004
E791
E687
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I Charm semileptonic decay as tests of LQCD
The decay rates are computed from first
principles (Feynman diagrams) using CKM matrix
elements.
f, etc.
The hadronic complications are contained in the
form factors, which can be calculated via
non-perturbative Lattice QCD, HQET or quark
models.
Charm SL decays provide a high quality lattice
calibration, which is crucial in reducing
systematic errors in the Unitarity Triangle. The
techniques validated by charm decays can be
applied to beauty decays.
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II Pseudoscalar l n decays
Simple kinematics ? Easy to extract form factors.
is the easiest point for LQCD calculation.
But a major disconnection exists between
experiment and theory. In the past, theories
worked best where experiments worked worst.
P at rest in D frame
hep-lat/0309107 preliminary
The lattice community is actively fixing the
situation and calculating f as a function of q2.
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Comparing Pole versus ISGW forms in D?pln
f(q2) parameterization
Until quite recently one required a specific
parameterized form to bridge the gap between a
theory and an experiment, since neither an
experiment nor a theory had clean f(q2)
information.
pole
ISGW1
ISGW2
Updated one.
The difference between these forms can be quite
dramatic in pmn decays.
Especially since pmn decay gets quite close to
the D pole.
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Brand new q2 information in D?pln/Kln
Preliminary Cleo 2004 pen pole mass is
It disfavors ISGW2 form by 4.2s
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Summary of D?pln/Kln Results
Kln
BR
Consistent w/ SU(3) breaking
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III D?vector m n decays
H0(q2), H(q2), H-(q2) are helicity-basis form
factors computable by LQCD
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Interference in D? K mn
Focus K signal
Yield 31,254
DataMC
K mn interferes with S- wave Kp and creates a
forward-backward asymmetry in the K decay angle
with a mass variation due to the varying BW
phase.
The S-wave amplitude is about 7 of the (H0) K
BW with a 45o relative phase
Its the same relative phase as the LASS (1988)
(2002)
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Kmn form factors
Results are getting very precise and unquenched
calculations for incisive tests of the theory
would be very desirable.
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Direct measurement of G (D?Kmn / Kmn)
Old quark model
Use upstream Ks (10) so that both the
numerator (Kpmn) and denominator (Ks mn) leave
3 tracks in FOCUS m-strip
S-wave corrected
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The Ds ? fmn form factor enigma
Ds ? fmn versus D ?Kln
circa 1999
circa 2004
Theoretically, the Ds?fln form factors should be
within 10 of D ?Kln . The rV values were
consistent, but r2 for Ds?fln was 2 ? higher
than D ?Kln .
But the (2004) FOCUS measurement obtained a
consistent r2 value as well!
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The future of charm SL physics
Cleo-c and Bes III Run at Y(3770) with high
luminosity and modern detectors.
Precision neutrino closure in D ?pen.
The q2 impasse afflicting SL data for the last 20
years shall be solved, finally.
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Summary
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G (D?Kmn / Kmn) circa 1993
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Some more tests of the Kmn model
Generally the model tracks the data rather well
Focus has a preliminary analysis of the K0 line
shape. G(K0) is seen as less than PDG by 1.6
MeV.