Some topics on D and Ds decays
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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
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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.
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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)
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Leptonic decays of D(Ds)->lν
Simple in theory, tree dominated, one mesondecay constants Clean in experiment.
Precision test of lattice QCD.
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HPQCD+UKQCD (unquenched) in 2007 PRL (2008)
Experiment Rosner, et al., PDG08
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A Puzzle?
Most model predictions are smaller than exp. 3σ deviations between experiment and lattice results.
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Light-front method
Dirac’s three forms of Hamiltonian dynamics( S. Brodsky et al., Phys.Rep.301(1998) 299 )
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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
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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.
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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.
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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.
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The semi-leptonic modes are chosen to have the same quark diagrams as the leptonic decays.
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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).
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Structure of f0(980) from Ds decays
Mass: below 1GeVIsosinglet scalar meson state.
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(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)?
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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.
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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.
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Using LFQM, Ds->f0(980) form factors are calculated.
The ssbar is not the dominant component.
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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.
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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)
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The mixing angle (by fit):
φ=(39.31.0)o, Feldmann (1999)
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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