1. Some topics on D and Ds decays
Zheng-Tao Wei
Nankai University
2010高能物理学会第八届全国会员代表大会, , 南昌

2. η-η’ mixing from D and Ds decays Summary
H.W. Ke, X.Q. Li, Wei,
PRD 80, (2009);
PRD 80, (2009);
arXiv:
Introduction
fDs puzzle
f0(980) from Ds decays
η-η’ mixing from D and Ds decays
Summary

3. Introduction Charm physics has been entered into a
second “Golden age” .
1. D0-D0bar mixing (2007)
2. New charmed resonances, DsJ, X, Y , Z….
Non-pertuebative QCD and New Physics
X. Li, X. Liu, Wei, FP (2009)

4. Leptonic decays of D(Ds)->lν
Simple in theory, tree dominated,
one mesondecay constants
Clean in experiment.
 Precision test of lattice QCD.

5. Experiment HPQCD+UKQCD (unquenched) in 2007 PRL (2008)
Rosner, et al., PDG08

6. A Puzzle? Most model predictions are smaller than exp.
3σ deviations between experiment and lattice results.

7. Light-front method
Dirac’s three forms of Hamiltonian dynamics ( S. Brodsky et al., Phys.Rep.301(1998) 299 )

8. Advantage of LF framework
LF method provides an appropriate non-perturbative
method to treat the low energy hadron phenomenon.
LF Fock space expansion provides a convenient description
of a hadron in terms of the fundamental quark and gluon
degrees of freedom.
The LF wave functions is Lorentz invariant.
ψ(xi, k┴i ) is independent of the bound state momentum.

9. Basic assumptions of LF quark model
Valence quark contribution dominates.
The quark mass is constitute mass which absorbs
some dynamic effects.
LC wave functions are Gaussian.
Choose Gaussian-type wave function
The parameter β determines the confinement scale.

10. The pseudoscalar meson decay constant is
with
Model I: fD=200 MeV, fDs=230 MeV;
Model II: fD=221 MeV, fDs=270 MeV.

11. It is not difficult to adjust parameters β to fit the data.
One prediction is that D->τν is 1.2*10^{-3 },
which will be observed soon.

12. The semi-leptonic modes are chosen to have the
same quark diagrams as the leptonic decays.

13. Chared Higgs model in 2HDM is excluded due to
New physics scenarios
Chared Higgs model in 2HDM is excluded due to
its destructive interference effects.
Lepto-quark model
Unparticle physics
Dobrescu, et al., PRL (2008);
Chen, et al., PRD (2007).

14. Structure of f0(980) from Ds decays
Mass: below 1GeV
Isosinglet scalar meson state.

15. What are the components of f0(980)?
Four quark state: qq qbarqbar; Jaffe (1977)
φ->f0γ;
Kkbar molecular state; Weinstein and Isgar (1982)
close to the threshold of Kkbar, J/ψ->φππ and Ds decays.
f0 has a large ssbar component.
glueball? Jaffe, et al., (1976).
lattice calculation does not support it.
Conventional quark model with qqbar component,
mix with σ(f0(600)).

16. Advantages of using Ds semi-leptonic decays
sbar
sbar
Ideal place to determine the ssbar component of f0(980).
Small strong uncertainties compared to the exclusive modes.

17. Scenario of quark-antiquark structure
In literature, the mixing angle φ
(233)o, f0->ππ, Scadron et al. (2009) φ=
(1426)o , φ->f0γ, f0->γγ, Anisovich et al. (2002)
(325)o , Ds->f0+M, El-Bennich et al. (2009)
They favor that ssbar is dominant.

18. Using LFQM, Ds->f0(980) form factors are calculated.
The ssbar is not the dominant component.

20. η- η’ mixing from D and Ds decays
η- η’ mixing plays an important role:
Chiral symmetry breaking
QCD anomaly
1997, B->η’K anomaly.
In the SU(3) quark model,
where θ is the nonet mixing angle with the range of -10o to -23o.

21. Another form is also widely used,
The relation between the two mixing form
Mixing angle θ=-11.7o corresponds to φ=43.0o.
Rosner (2009)

22. The mixing angle (by fit):
φ=(39.31.0)o, Feldmann (1999)

25. Summary The “fDs puzzle” can be explained in SM with the
light-front approach.
The semi-leptonic decay of D and Ds provides a clean
way to determine the mixing parameter in f0(980)
and η-η’ mixing .
The ssbar component is not dominant in f0(980).
Our result on η-η’ mixing is consistent with the
previous study.