Semileptonic Charm Decays and QCD. Doris Y. Kim, University of Illinois Urbana-Champaign. Content Part I : Theories of Charm Semileptonic decays Part II : q 2 dependence in Pseudo-scalar l n decays . Part III : Vector l n decays . D + K* 0 m n analysis (not so simple!)
Doris Y. Kim, University of Illinois Urbana-Champaign
ISMD Sonoma July 27, 2004
The decay rates are computed from first principles (Feynman diagrams) using CKM matrix elements.
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.
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
The lattice community is actively fixing the situation and calculating f+ as a function of q2.
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.
The difference between these forms can be quite dramatic in pmndecays.
Especially since pmndecay gets quite close to the D* pole.
form factor f+(q²)
Based on 820 events
Preliminary K mn
q² / GeV²
q² / GeV²
Preliminary Cleo 2004 pen pole mass is
It disfavors ISGW2 form by ~4.2s
Clearly the data does not favor the simple Ds* pole
A big advance in precision!
Consistent w/ SU(3) breaking
Two amplitudes get sumed over W polarization using D-matrices
Helicity FF are combinations of one vector and two axial form factors.
Two observables parameterize the decay
H0(q2), H+(q2), H-(q2) are helicity-basis form factors computable by LQCD
-15% F-B asymmetry!
Focus “K*” signal
K* mn interferes with S- wave Kp and creates a forward-backward asymmetry in the K* decay angle with a mass variationdue to the varying BW phase.
The S-wave amplitude is about 7% of the (H0) K* BW with a 45o relative phase
It’s the same relative phase as the LASS (1988)
Precision tests of the model.
Due to interference
Results are getting very precise and unquenched calculations for incisive tests of the theory would be very desirable.
Old quark model
Use upstream Ks (~10%) so that both the numerator (Kpmn) and denominator (Ksmn) leave 3 tracks in FOCUS m-strip
Ds fmnversusD+ K*ln
Theoretically, the Dsflnform factors should be within 10% of D+ K*ln . The rV values were consistent, but r2 for Dsflnwas 2 higher than D+ K*ln .
But the (2004) FOCUS measurement obtained a consistent r2 value as well!
Extremely clean events!
Prelim. data (60 pb-1)
CLEO-c yellow book:1 fb-1
U = Emiss - Pmiss
U = Emiss - Pmiss
Yellow book1 fb-1 (MC)
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.
New CLEO 2004 Dpen/Ken result
V(q20) problem D+ K* mn
in D+ K* mn
Consistent FF for D+ K* mn&Ds+f mn
A dramatic mismatch is seen at very low q2 suggesting a V(q20) problem
Generally the model tracks the data rather well…
Focus has a preliminary analysis of the K*0 line shape. G(K*0)is seen as less than PDG by~1.6 MeV.