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Register a new userNucleon and $Omega$ Baryon Masses with All-HISQ Fermions at the Physical Point
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We present the results of the nucleon and $Omega$ baryon masses using staggered action for both valence and sea quarks. Three ensembles with the physical pion mass at approximate lattice spacings of $0.15$, $0.12$, and $0.088$fm are employed to extrapolate the masses to continuum and we obtain $M_N = 964(16)$ MeV and $M_Omega = 1678(9)$. Both statistical and systematic uncertainties are included in the nucleon mass, whereas only the statistical uncertainty is accounted for in the $Omega$ baryon mass.
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In lattice QCD, both direct method and HAL QCD method are used to investigate the two-baryon systems. We show that due to the contamination of the scattering excited states, it is challenging to measure the eigenenergy from the temporal correlation in the direct method, while the HAL QCD method can extract the information of the interaction from both scattering states and ground state by using the spatial correlation. We examine the systematic uncertainty of the derivative expansion in the HAL QCD method, which is found to be well under control at the low energies. By using the time-dependent HAL QCD method, we study the nucleon($N$)-Omega($Omega$) system in the $^5$S$_2$ channel with almost physical quark masses at $m_pi simeq 146$ MeV. We find the interaction is attractive at all distances, which produces a quasi-bound state with the binding energy 1.54(0.30)($^{+0.04}_{-0.10}$) MeV. We also consider the extra Coulomb interaction in the $pOmega^{-}$($^5$S$_2$) system, whose binding energy becomes 2.46(0.34)($^{+0.04}_{-0.01}$) MeV. $NOmega$($^5$S$_2$) dibaryon could be searched through two-particle correlations in the heavy ion collision experiments.
We discuss the reduction of errors in the calculation of the form factor $f_+^{K pi}(0)$ with HISQ fermions on the $N_f=2+1+1$ MILC configurations from increased statistics on some key ensembles, new data on ensembles with lattice spacings down to 0.042 fm and the study of finite-volume effects within staggered ChPT. We also study the implications for the unitarity of the CKM matrix in the first row and for current tensions with leptonic determinations of $vert V_{us}vert$.
We present results for the nucleon electromagnetic and axial form factors using an N$_f$=2 twisted mass fermion ensemble with pion mass of about 131 MeV. We use multiple sink-source separations to identify excited state contamination. Dipole masses for the momentum dependence of the form factors are extracted and compared to experiment, as is the nucleon magnetic moment and charge and magnetic radii.
We present results on the spin and quark content of the nucleon using $N_f=2$ twisted mass clover-improved fermion simulations with a pion mass close to its physical value. We use recently developed methods to obtain accurate results for both connected and disconnected contributions. We provide results for the axial charge, quark and gluon momentum fraction as well as the light, strange and charm $sigma$-terms.
The quark flavor sector of the Standard Model is a fertile ground to look for new physics effects through a unitarity test of the Cabbibo-Kobayashi-Maskawa (CKM) matrix. We present a lattice QCD calculation of the scalar and the vector form factors (over a large $q^2$ region including $q^2 = 0$) associated with the $D rightarrow Kl{ u}$ semi-leptonic decay. This calculation will then allow us to determine the central CKM matrix element, $V_{cs}$ in the Standard Model, by comparing the lattice QCD results for the form factors and the experimental decay rate. This form factor calculation has been performed on the $N_f =2+1+1$ MILC HISQ ensembles with the physical light quark masses.
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