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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 : q 2 dependence in Pseudo-scalar l n decays . Part III : Vector l n decays . D +  K* 0 m n analysis (not so simple!)

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semileptonic charm decays and qcd
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+  K*0mn analysis (not so simple!)
    • Form factors ofDs  f mn
  • Part V: Future of Semileptonic decays.

ISMD Sonoma July 27, 2004



i charm semileptonic decay as tests of lqcd
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.

ii pseudoscalar l n decays
II: Pseudoscalar ln decays

cleanest theory

highest rate

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.

comparing pole versus isgw forms in d p l n
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.




Updated one.

The difference between these forms can be quite dramatic in pmndecays.

Especially since pmndecay gets quite close to the D* pole.

brand new q 2 information in d p l n kl n
Brand new q2 information in Dpln/Kln



form factor f+(q²)

Based on 820 events


single-pole model

Preliminary K mn


q² / GeV²

single-pole model

q² / GeV²

Preliminary Cleo 2004 pen pole mass is

It disfavors ISGW2 form by ~4.2s

summary of d p l n kl n results
Summary of Dpln/Kln Results

Clearly the data does not favor the simple Ds* pole

A big advance in precision!



Consistent w/ SU(3) breaking

iii d vector m n decays
III: Dvector mn decays

left-handed m+

Two amplitudes get sumed over W polarization using D-matrices

right-handed m+

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

interference in d k mn
Interference in D+ K* mn

F-B asymmetry

-15% F-B asymmetry!

matches model

Focus “K*” signal

Yield 31,254


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)


k mn form factors
K*mn form factors

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.

direct measurement of g d k mn k mn
Direct measurement of G (D+K*mn / Kmn)


Old quark model

Use upstream Ks (~10%) so that both the numerator (Kpmn) and denominator (Ksmn) leave 3 tracks in FOCUS m-strip

S-wave corrected

the d s fmn form factor enigma
The Ds fmn form factor enigma

Ds fmnversusD+ K*ln

circa 1999

circa 2004

Theoretically, the Dsflnform factors should be within 10% of D+ K*ln . The rV values were consistent, but r2 for Dsflnwas 2  higher than D+ K*ln .

But the (2004) FOCUS measurement obtained a consistent r2 value as well!

the future of charm sl physics
The future of charm SL physics

yDoDo, DoK-p+

Extremely clean events!


Prelim. data (60 pb-1)

CLEO-c yellow book:1 fb-1





Pavlunin APS(2004)

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 Dpen/Ken result

q2< 0.2

F-B asymmetry

V(q20) problem D+ K* mn

s-wave interference

in D+ K* mn

V/PS ratio

Consistent FF for D+ K* mn&Ds+f mn

some more tests of the k mn model
Some more tests of the K*mn model

A dramatic mismatch is seen at very low q2 suggesting a V(q20) 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.