The lowest-lying glueballs are investigated in lattice QCD using N f = 2 clover Wilson fermion on anisotropic lattices. We simulate at two different and relatively heavy quark masses, corresponding to physical pion mass of mπ ∼ 938 MeV and 650 MeV. The quark mass dependence of the glueball masses have not been investigated in the present study. Only the gluonic operators built from Wilson loops are utilized in calculating the corresponding correlation functions. In the tensor channel, we obtain the ground state mass to be 2.363(39) GeV and 2.384(67) GeV at mπ ∼ 938 MeV and 650 MeV, respectively. In the pseudoscalar channel, when using the gluonic operator whose continuum limit has the form of ijk T rBiDjB k , we obtain the ground state mass to be 2.573(55) GeV and 2.585(65) GeV at the two pion masses. These results are compatible with the corresponding results in the quenched approximation. In contrast, if we use the topological charge density as field operators for the pseudoscalar, the masses of the lowest state are much lighter (around 1GeV) and compatible with the expected masses of the flavor singlet qq meson. This indicates that the operator ijk T rBiDjB k and the topological charge density couple rather differently to the glueball states and qq mesons. The observation of the light flavor singlet pseudoscalar meson can be viewed as the manifestation of effects of dynamical quarks. In the scalar channel, the ground state masses extracted from the correlation functions of gluonic operators are determined to be around 1.4-1.5 GeV, which is close to the ground state masses from the correlation functions of the quark bilinear operators. In all cases, the mixing between glueballs and conventional mesons remains to be further clarified in the future.
We propose a strategy to access the qq component of the ρ resonance in lattice QCD. Through a mixed action formalism (overlap valence on domain wall sea), the energy of the qq component is derived at different valence quark masses, and shows a linear dependence on m 2 π . The slope is determined to be c1 = 0.505(3) GeV −1 , from which the valence πρ sigma term is extracted to be σ (val) πρ = 9.82(6) MeV using the Feynman-Hellman theorem. At the physical pion mass, the mass of the qq component is interpolated to be mρ = 775.9 ± 6.0 ± 1.8 MeV, which is close to the ρ resonance mass. We also obtain the leptonic decay constant of the qq component to be f ρ − = 208.5 ± 5.5 ± 0.9 MeV, which can be compared with the experimental value f exp ρ ≈ 221 MeV through the relation f exp ρ = Zρf ρ ± with Zρ ≈ 1.13 being the on-shell wavefunction renormalization of ρ owing to the ρ − π interaction. We emphasize that mρ and fρ of the qq component, which are obtained for the first time from QCD, can be taken as the input parameters of ρ in effective field theory studies where ρ acts as a fundamental degree of freedom.
The Ω baryons with J P = 3/2 ± , 1/2 ± are studied on the lattice in the quenched approximation. Their mass levels are ordered as M 3/2 + < M 3/2 − ≈ M 1/2 − < M 1/2 + , as is expected from the constituent quark model. The mass values are also close to those of the four Ω states observed in experiments, respectively. We calculate the Bethe-Salpeter amplitudes of Ω(3/2 + ) and Ω(1/2 + ) and find there is a radial node for the Ω(1/2 + ) Bethe-Salpeter amplitude, which may imply that Ω(1/2 + ) is an orbital excitation of Ω baryons as a member of the (D, L P N ) = (70, 0 + 2 ) supermultiplet in the SU (6) O(3) quark model description. Our results are helpful for identifying the quantum numbers of experimentally observed Ω states.
While the standard model is the most successful theory to describe all the interactions and constituents of elementary particle physics, it has been constantly scrutinized for over four decades. Weak decays of charm quarks can be used to measure the coupling strength between quarks in different families and serve as an ideal probe for CP violation. As the lowest charm-strange baryons with three different flavors,
baryons (composed of
or
) have been extensively studied in experiments. In this study, we use state-of-the-art lattice QCD techniques to generate 2+1 clover fermion ensembles with two lattice spacings,
. Then, we present the first ab-initio lattice QCD calculation of the
form factors. Our theoretical results for the
decay widths are consistent with and approximately two times more precise than the latest measurements by the ALICE and Belle collaborations. Based on the latest experimental measurements, we independently obtain the quark-mixing matrix element
, which is in good agreement with results from other theoretical approaches.
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