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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 : 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

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  1. 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 E687 E791

  2. 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.

  3. 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.

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

  5. Brand new q2 information in Dpln/Kln pen Ken form factor f+(q²) Based on 820 events Kln single-pole model Preliminary K mn pln q² / GeV² single-pole model q² / GeV² Preliminary Cleo 2004 pen pole mass is It disfavors ISGW2 form by ~4.2s

  6. Summary of Dpln/Kln Results Clearly the data does not favor the simple Ds* pole A big advance in precision! Kln BR Consistent w/ SU(3) breaking

  7. 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

  8. Interference in D+ K* mn F-B asymmetry -15% F-B asymmetry! matches model 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 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) (2002)

  9. K*mn form factors Precision tests of the model. Due to interference acoplanarity Results are getting very precise and unquenched calculations for incisive tests of the theory would be very desirable.

  10. Direct measurement of G (D+K*mn / Kmn) Theory 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

  11. 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!

  12. The future of charm SL physics yDoDo, DoK-p+ Extremely clean events! K+ Prelim. data (60 pb-1) CLEO-c yellow book:1 fb-1 p+ K- p- MC 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.

  13. Summary 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

  14. G (D+K*mn / Kmn) circa 1993 circa 1993

  15. 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.

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