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 , 2010.4.17-21, 南昌

Introduction

fDs puzzle

f0(980) from Ds decays

η-η’ mixing from D and Ds decays

Summary

H.W. Ke, X.Q. Li, Wei, PRD 80, 015002 (2009); PRD 80, 074030 (2009); arXiv:0912.4094.

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)

Leptonic decays of D(Ds)->lν

Simple in theory, tree dominated, one mesondecay constants Clean in experiment.

Precision test of lattice QCD.

HPQCD+UKQCD (unquenched) in 2007 PRL (2008)

Experiment Rosner, et al., PDG08

A Puzzle?

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

Light-front method

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

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.

Advantage of LF framework

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.

with

The pseudoscalar meson decay constant is

)1(21 xmxmA

Model I: fD=200 MeV, fDs=230 MeV;

Model II: fD=221 MeV, fDs=270 MeV.

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.

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

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).

Structure of f0(980) from Ds decays

Mass: below 1GeVIsosinglet scalar meson state.

(1) Four quark state: qq qbarqbar; Jaffe (1977) φ->f0γ;

(2) 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.

(3) glueball? Jaffe, et al., (1976). lattice calculation does not support it.

(4)Conventional quark model with qqbar component, mix with σ(f0(600)).

What are the components of f0(980)?

c s

sbar sbar

f0(980)Ds

Advantages of using Ds semi-leptonic decays

Ideal place to determine the ssbar component of f0(980).

Small strong uncertainties compared to the exclusive modes.

Scenario of quark-antiquark structure

In literature, the mixing angle φ

φ=

(233)o, f0->ππ, Scadron et al. (2009)

(1426)o , φ->f0γ, f0->γγ, Anisovich et al. (2002)

(325)o , Ds->f0+M, El-Bennich et al. (2009)

They favor that ssbar is dominant.

Using LFQM, Ds->f0(980) form factors are calculated.

The ssbar is not the dominant component.

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.

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)

The mixing angle (by fit):

φ=(39.31.0)o, Feldmann (1999)

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.

Summary