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Register a new userConstraints on charm-anticharm asymmetry in the nucleon from lattice QCD
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We present the first lattice QCD calculation of the charm quark contribution to the nucleon electromagnetic form factors $G^c_{E,M}(Q^2)$ in the momentum transfer range $0leq Q^2 leq 1.4$ $rm GeV^2$. The quark mass dependence, finite lattice spacing and volume corrections are taken into account simultaneously based on the calculation on three gauge ensembles including one at the physical pion mass. The nonzero value of the charm magnetic moment $mu^c_M=-0.00127(38)_{rm stat}(5)_{rm sys}$, as well as the Pauli form factor, reflects a nontrivial role of the charm sea in the nucleon spin structure. The nonzero $G^c_{E}(Q^2)$ indicates the existence of a nonvanishing asymmetric charm-anticharm sea in the nucleon. Performing a nonperturbative analysis based on holographic QCD and the generalized Veneziano model, we study the constraints on the $[c(x)-bar{c}(x)]$ distribution from the lattice QCD results presented here. Our results provide complementary information and motivation for more detailed studies of physical observables that are sensitive to intrinsic charm and for future global analyses of parton distributions including asymmetric charm-anticharm distribution.
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A pair of triply charmed baryons, $Omega_{ccc}Omega_{ccc}$, is studied as an ideal dibaryon system by (2+1)-flavor lattice QCD with nearly physical light-quark masses and the relativistic heavy quark action with the physical charm quark mass. The spatial baryon-baryon correlation is related to their scattering parameters on the basis of the HAL QCD method. The $Omega_{ccc}Omega_{ccc}$ in the ${^1S_0}$ channel taking into account the Coulomb repulsion with the charge form factor of $Omega_{ccc}$ leads to the scattering length $a^{rm C}_0simeq -19~text{fm}$ and the effective range $r^{rm C}_{mathrm{eff}}simeq 0.45~text{fm}$. The ratio $r^{rm C}_{mathrm{eff}}/a^{rm C}_0 simeq -0.024$, whose magnitude is considerably smaller than that of the dineutron ($-0.149$), indicates that $Omega_{ccc}Omega_{ccc}$ is located in the unitary regime.
We determine within lattice QCD, the nucleon spin carried by valence and sea quarks, and gluons. The calculation is performed using an ensemble of gauge configurations with two degenerate light quarks with mass fixed to approximately reproduce the physical pion mass. We find that the total angular momentum carried by the quarks in the nucleon is $J_{u+d+s}{=}0.408(61)_{rm stat.}(48)_{rm syst.}$ and the gluon contribution is $J_g {=}0.133(11)_{rm stat.}(14)_{rm syst.}$ giving a total of $J_N{=}0.54(6)_{rm stat.}(5)_{rm syst.}$ consistent with the spin sum. For the quark intrinsic spin contribution we obtain $frac{1}{2}Delta Sigma_{u+d+s}{=}0.201(17)_{rm stat.}(5)_{rm syst.}$. All quantities are given in the $overline{textrm{MS}}$ scheme at 2~GeV. The quark and gluon momentum fractions are also computed and add up to $langle xrangle_{u+d+s}+langle xrangle_g{=}0.804(121)_{rm stat.}(95)_{rm syst.}+0.267(12)_{rm stat.}(10)_{rm syst.}{=}1.07(12)_{rm stat.}(10)_{rm syst.}$ satisfying the momentum sum.
In the past year, we calculated with lattice QCD three quantities that were unknown or poorly known. They are the $q^2$ dependence of the form factor in semileptonic $Dto Kl u$ decay, the decay constant of the $D$ meson, and the mass of the $B_c$ meson. In this talk, we summarize these calculations, with emphasis on their (subsequent) confirmation by experiments.
We present results for the moments of nucleon isovector vector and axial generalised parton distribution functions computed within lattice QCD. Three ensembles of maximally twisted mass clover-improved fermions simulated with a physical value of the pion mass are analyzed. Two of these ensembles are generated using two degenerate light quarks. A third ensemble is used having, in addition to the light quarks, strange and charm quarks in the sea. A careful analysis of the convergence to the ground state is carried out that is shown to be essential for extracting the correct nucleon matrix elements. This allows a controlled determination of the unpolarised, helicity and tensor second Mellin moments. The vector and axial-vector generalised form factors are also computed as a function of the momentum transfer square up to about 1 GeV$^2$. The three ensembles allow us to check for unquenching effects and to assess lattice finite volume effects.
In this study, we present a determination of the unpolarized gluon Ioffe-time distribution in the nucleon from a first principles lattice quantum chromodynamics calculation. We carry out the lattice calculation on a $32^3times 64$ ensemble with a pion mass of $358$ MeV and lattice spacing of $0.094$ fm. We construct the nucleon interpolating fields using the distillation technique, flow the gauge fields using the gradient flow, and solve the summed generalized eigenvalue problem to determine the glounic matrix elements. Combining these techniques allows us to provide a statistically well-controlled Ioffe-time distribution and unpolarized gluon PDF. We obtain the flow time independent reduced Ioffe-time pseudo-distribution, and calculate the light-cone Ioffe-time distribution and unpolarized gluon distribution function in the $overline{rm MS}$ scheme at $mu = 2$ GeV, neglecting the mixing of the gluon operator with the quark singlet sector. Finally, we compare our results to phenomenological determinations.
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