Some topics on D and Ds decays

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

H.W. Ke, X.Q. Li, Wei, PRD 80, 015002 (2009); PRD 80, 074030 (2009); arXiv:0912.4094. • Introduction • fDs puzzle • f0(980) from Ds decays • η-η’ mixing from D and Ds decays • Summary

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 mesondecay 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 )

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.

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.

The pseudoscalar meson decay constant is with 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 1GeV Isosinglet scalar meson state.

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)).

Advantages of using Ds semi-leptonic decays c s Ds f0(980) sbar sbar • 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 (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.

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=(39.31.0)o, Feldmann (1999)

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.

Some topics on D and Ds decays