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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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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.
We evaluate the spin-$3/2 to$ spin-$1/2$ electromagnetic transitions of the doubly charmed baryons on 2+1 flavor, $32^3 times 64$ PACS-CS lattices with a pion mass of $156(9)$ MeV/c$^2$. A relativistic heavy quark action is employed to minimize the associated systematic errors on charm-quark observables. We extract the magnetic dipole, $M1$, and the electric quadrupole, $E2$, transition form factors. In order to make a reliable estimate of the $M1$ form factor, we carry out an analysis by including the effect of excited-state contributions. We find that the $M1$ transition is dominant and light degrees of freedom ($u/d$- or $s$-quark) play the leading role. $E2$ form factors, on the other hand, are found to be negligibly small, which in turn, have minimal effect on the helicity and transition amplitudes. We predict the decay widths and lifetimes of $Xi_{cc}^{ast +,++}$ and $Omega_{cc}^{ast +}$ based on our results. Finite size effects on these ensembles are expected to be around 1%. Differences in kinematical and dynamical factors with respect to the $NgammatoDelta$ transition are discussed and compared to non-lattice determinations as well keeping possible systematic artifacts in mind. A comparison to $Omega_c gamma rightarrow Omega_c^ast$ transition and a discussion on systematic errors related to the choice of heavy quark action are also given. Results we present here are particularly suggestive for experimental facilities such as LHCb, PANDA, Belle II and BESIII to search for further states.
We explore the use of optimized operators, designed to interpolate only a single meson eigenstate, in three-point correlation functions with a vector-current insertion. These operators are constructed as linear combinations in a large basis of meson interpolating fields using a variational analysis of matrices of two-point correlation functions. After performing such a determination at both zero and non-zero momentum, we compute three-point functions and are able to study radiative transition matrix elements featuring excited state mesons. The required two- and three-point correlation functions are efficiently computed using the distillation framework in which there is a factorization between quark propagation and operator construction, allowing for a large number of meson operators of definite momentum to be considered. We illustrate the method with a calculation using anisotopic lattices having three flavors of dynamical quark all tuned to the physical strange quark mass, considering form-factors and transitions of pseudoscalar and vector meson excitations. The dependence on photon virtuality for a number of form-factors and transitions is extracted and some discussion of excited-state phenomenology is presented.
We study hadron properties near the deconfining transition in the finite temperature lattice QCD. This paper focus on the heavy quarkonium states, such as $J/psi$ meson. We compare the meson correlators above and below $T_c$ and discuss the possibility of the $cbar{c}$ bound state by observing the wave function.
Working with a large basis of covariant derivative-based meson interpolating fields we demonstrate the feasibility of reliably extracting multiple excited states using a variational method. The study is performed on quenched anisotropic lattices with clover quarks at the charm mass. We demonstrate how a knowledge of the continuum limit of a lattice interpolating field can give additional spin-assignment information, even at a single lattice spacing, via the overlap factors of interpolating field and state. Excited state masses are systematically high with respect to quark potential model predictions and, where they exist, experimental states. We conclude that this is most likely a result of the quenched approximation.
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