Lattice QCD evaluation of the Compton amplitude employing the Feynman-Hellmann theorem

The forward Compton amplitude describes the process of virtual photon scattering from a hadron and provides an essential ingredient for the understanding of hadron structure. As a physical amplitude, the Compton tensor naturally includes all target mass corrections and higher twist effects at a fixed virtuality, $Q^2$. By making use of the second-order Feynman-Hellmann theorem, the nucleon Compton tensor is calculated in lattice QCD at an unphysical quark mass across a range of photon momenta $3 lesssim Q^2 lesssim 7$ GeV$^2$. This allows for the $Q^2$ dependence of the low moments of the nucleon structure functions to be studied in a lattice calculation for the first time. The results demonstrate that a systematic investigation of power corrections and the approach to parton asymptotics is now within reach.

Radiative transitions of doubly charmed baryons in lattice QCD

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.

$Xi_c gamma rightarrowXi^prime_c$ transition in lattice QCD

We evaluate the electromagnetic $Xi_c gamma rightarrowXi_c^prime$ transition on 2+1 flavor lattices corresponding to a pion mass of $sim 156$ MeV. We extract the magnetic Sachs and Pauli form factors which give the $Xi_c$-$Xi_c^prime$ transition magnetic moment and the decay rates of $Xi_c^prime$ baryons. We did not find a signal for the magnetic form factor of the neutral transition $Xi_c^0 gamma rightarrowXi_c^{prime 0}$, which is suppressed by the U-spin flavor symmetry. As a byproduct, we extract the magnetic form factors and the magnetic moments of $Xi_c$ and $Xi_c^prime$ baryons, which give an insight to the dynamics of $u/d$, $s$ and $c$ quarks having masses at different scales.

$Lambda_cSigma_cpi$ coupling and $Sigma_c rightarrowLambda_c pi$ decay in lattice QCD

We evaluate the $Lambda_cSigma_cpi$ coupling constant ($G_{Lambda_c Sigma_c pi}$) and the width of the strong decay $Sigma_c rightarrowLambda_c pi$ in 2+1 flavor lattice QCD on four different ensembles with pion masses ranging from 700 MeV to 300 MeV. We find $G_{Lambda_c Sigma_c pi}=18.332(1.476)_{rm{stat.}}(2.171)_{rm{syst.}}$ and the decay width $Gamma(Sigma_c rightarrowLambda_c pi)=1.65(28)_{rm{stat.}}(30)_{rm{syst.}}$~MeV on the physical quark-mass point, which is in agreement with the recent experimental determination.

A look inside charmed-strange baryons from lattice QCD

The electromagnetic form factors of the spin-3/2 $Omega$ baryons, namely $Omega$, $Omega_c^ast$, $Omega_{cc}^ast$ and $Omega_{ccc}$, are calculated in full QCD on $32^3times 64$ PACS-CS lattices with a pion mass of 156(9) MeV. The electric charge radii and magnetic moments from the $E0$ and $M1$ multipole form factors are extracted. Results for the electric quadrupole form factors, $E2$, are also given. Quark sector contributions are computed individually for each observable and then combined to obtain the baryon properties. We find that the charm quark contributions are systematically smaller than the strange-quark contributions in the case of the charge radii and magnetic moments. $E2$ moments of the $Omega_{cc}^ast$ and $Omega_{ccc}$ provide a statistically significant data to conclude that their electric charge distributions are deformed to an oblate shape. Properties of the spin-1/2 $Omega_c$ and $Omega_{cc}$ baryons are also computed and a thorough comparison is given. This complete study gives valuable hints about the heavy-quark dynamics in charmed hadrons.

$Omega_c gamma rightarrowOmega_c^ast$ transition in lattice QCD

We study the electromagnetic $Omega_c gamma rightarrowOmega_c^ast$ transition in 2+1 flavor lattice QCD, which gives access to the dominant decay mode of $Omega_c^ast$ baryon. The magnetic dipole and the electric quadrupole transition form factors are computed. The magnetic dipole form factor is found to be mainly determined by the strange quark and the electric quadrupole form factor to be negligibly small, in consistency with the quark model. We also evaluate the helicity amplitudes and the decay rate.

Electromagnetic structure of charmed baryons in Lattice QCD

As a continuation of our recent work on the electromagnetic properties of the doubly charmed $Xi_{cc}$ baryon, we compute the charge radii and the magnetic moments of the singly charmed $Sigma_c$, $Omega_c$ and the doubly charmed $Omega_{cc}$ baryons in 2+1 flavor Lattice QCD. In general, the charmed baryons are found to be compact as compared to the proton. The charm quark acts to decrease the size of the baryons to smaller values. We discuss the mechanism behind the dependence of the charge radii on the light valence- and sea-quark masses. The magnetic moments are found to be almost stable with respect to changing quark mass. We investigate the individual quark sector contributions to the charge radii and the magnetic moments. The magnetic moments of the singly charmed baryons are found to be dominantly determined by the light quark and the role of the charm quark is significantly enhanced for the doubly charmed baryons.

Electromagnetic properties of doubly charmed baryons in Lattice QCD

We compute the electromagnetic properties of Xi_cc baryons in 2+1 flavor Lattice QCD. By measuring the electric charge and magnetic form factors of Xi_cc baryons, we extract the magnetic moments, charge and magnetic radii as well as the Xi_cc Xi_cc rho coupling constant, which provide important information to understand the size, shape and couplings of the doubly charmed baryons. We find that the two heavy charm quarks drive the charge radii and the magnetic moment of Xi_cc to smaller values as compared to those of, e.g., the proton.

Vector and axial-vector couplings of D and D* mesons in 2+1 flavor Lattice QCD

Using the axial-vector coupling and the electromagnetic form factors of the D and D* mesons in 2+1 flavor Lattice QCD, we compute the D*Dpi, DDrho and D*D*rho coupling constants, which play an important role in describing the charm hadron interactions in terms of meson-exchange models. We also extract the charge radii of D and D* mesons and determine the contributions of the light and charm quarks separately.