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Register a new userRadiative transitions of charmonium states in the covariant confined quark model
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We have studied the dominant radiative transitions of the charmonium $S$- and $P$-wave states within the CCQM. The gauge invariant leading-order transition amplitudes have been expressed by using either the conventional Lorentz structures, or the helicity amplitudes, where it was effective. The renormalization couplings of the charmonium states have been strictly fixed by the compositeness conditions that excludes the constituent degrees of freedom from the space of physical states. We use the basic model parameters for the constituent c-quark mass $m_c=1.80$ GeV and the global infrared cutoff $lambda=0.181$ GeV. We additionally introduce only one adjustable parameter $varrho>0$ common for the the charmonium states $eta_c({}^1!S_0)$, $J/psi({}^3!S_1)$, $chi_{c0}({^{3}}!P_{0})$, $chi_{c1}({^{3}}!P_{1})$, $h_c({^{1}}!P_{1})$, and $chi_{c2}({^{3}}!P_{2})$ to describe the quark distribution inside the hadron. This parameter describes the ratio between the charmonium size and its physical mass. The optimal value $varrho=0.485$ has been fixed by fitting the latest data for the partial widths of the one-photon radiative decays of the triplet $chi_{cJ}({^{3}}!P_{J}),~J={0,1,2}$. Then, we calculate corresponding fractional widths for states $J/psi({}^3!S_1)$ and $h_c({^{1}}!P_{1})$. Estimated results are in good agreement with the latest data. By using the fraction data from PDG2020 and our estimated partial decay width for $h_c({^{1}}!P_{1})$ we recalculate the theoretical full width $Gamma^{rm theor}_{h_c} simeq ( 0.57 pm 0.12 )$ MeV in comparison with latest data $Gamma^{rm exp}_{h_c} simeq (0.7pm 0.4)$ MeV. We also repeated our calculations by gradually decreasing the global cutoff parameter and revealed that the results do not change for any $lambda<0.181$ GeV up to the deconfinement limit.
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The form factors for the radiative transitions between charmonium mesons are investigated. We employ an anisotropic lattice using a Wilson gauge action, and domain-wall fermion action. We extrapolate the form factors to $Q^2 = 0$, corresponding to a real photon, using quark-model-inspired functions. Finally, comparison is made with photocouplings extracted from the measured radiative widths, where known. Our preliminary results find photocouplings commensurate with these experimentally extracted values.
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Recently, the BESIII collaboration has reported numerous measurements of various $D_{(s)}$ meson semileptonic decays with significantly improved precision. Together with similar studies carried out at BABAR, Belle, and CLEO, new windows to a better understanding of weak and strong interactions in the charm sector have been opened. In light of new experimental data, we review the theoretical description and predictions for the semileptonic decays of $D_{(s)}$ to a pseudoscalar or a vector meson. This review is essentially an extended discussion of our recently published results obtained in the framework of the covariant confining quark model.
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