Showing papers by "Huey-Wen Lin published in 2010"

Nucleon structure from mixed action calculations using 2+1 flavors of asqtad sea and domain wall valence fermions

Abstract: We present high statistics results for the structure of the nucleon from a mixed-action calculation using 2+1 flavors of asqtad sea and domain-wall valence fermions. We perform extrapolations of our data based on different chiral effective field theory schemes and compare our results with available information from phenomenology. We discuss vector and axial form factors of the nucleon, moments of generalized parton distributions, including moments of forward parton distributions, and implications for the decomposition of the nucleon spin.

Nucleon isovector structure functions in (2+1)-flavor QCD with domain wall fermions

Abstract: We report on numerical lattice QCD calculations of some of the low moments of the nucleon structure functions. The calculations are carried out with gauge configurations generated by the RBC and UKQCD Collaborations with ($2+1$)-flavors of dynamical domain-wall fermions and the Iwasaki gauge action ($\ensuremath{\beta}=2.13$). The inverse lattice spacing is ${a}^{\ensuremath{-}1}=1.73\text{ }\text{ }\mathrm{GeV}$, and two spatial volumes of $(2.7\text{ }\text{ }\mathrm{fm}{)}^{3}$ and $(1.8\text{ }\text{ }\mathrm{fm}{)}^{3}$ are used. The up and down quark masses are varied so the pion mass lies between 0.33 and 0.67 GeV, while the strange mass is about 12% heavier than the physical one. The structure function moments we present include the fully nonperturbatively renormalized isovector quark momentum fraction $⟨x{⟩}_{u\ensuremath{-}d}$, the helicity fraction $⟨x{⟩}_{\ensuremath{\Delta}u\ensuremath{-}\ensuremath{\Delta}d}$, and transversity $⟨1{⟩}_{\ensuremath{\delta}u\ensuremath{-}\ensuremath{\delta}d}$, as well as an unrenormalized twist-3 coefficient ${d}_{1}$. The ratio of the momentum to helicity fractions, $⟨x{⟩}_{u\ensuremath{-}d}/⟨x{⟩}_{\ensuremath{\Delta}u\ensuremath{-}\ensuremath{\Delta}d}$, does not show dependence on the light quark mass and agrees well with the value obtained from experiment. Their respective absolute values, fully renormalized, show interesting trends toward their respective experimental values at the lightest quark mass. A prediction for the transversity, $0.7l⟨1{⟩}_{\ensuremath{\delta}u\ensuremath{-}\ensuremath{\delta}d}l1.1$, in the $\overline{\mathrm{MS}}$ scheme at 2 GeV is obtained. The twist-3 coefficient, ${d}_{1}$, though yet to be renormalized, supports the perturbative Wandzura-Wilczek relation.

Nucleon, $\Delta$ and $\Omega$ excited states in $N_f=2+1$ lattice QCD

Abstract: The energies of the excited states of the Nucleon, $$\Delta$$ and $$\Omega$$ are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The calculation is performed at three values of the light quark mass, corresponding to pion masses $$m_{\pi}$$ = 392(4), 438(3) and 521(3) MeV. We employ the variational method with a large basis of interpolating operators enabling six energies in each irreducible representation of the lattice to be distinguished clearly. We compare our calculation with the low-lying experimental spectrum, with which we find reasonable agreement in the pattern of states. In addition, the need to include operators that couple to the expected multi-hadron states in the spectrum is clearly identified.

Singly and Doubly Charmed J=1/2 Baryon Spectrum from Lattice QCD

Abstract: We compute the masses of the singly and doubly charmed baryons in full QCD using the relativistic Fermilab action for the charm quark. For the light quarks we use domain-wall fermions in the valence sector and improved Kogut-Susskind sea quarks. We use the low-lying charmonium spectrum to tune our heavy-quark action and as a guide to understanding the discretization errors associated with the heavy quark. Our results are in good agreement with experiment within our systematics. For the {Xi}{sub cc}, we find the isospin-averaged mass to be M{sub {Xi}{sub c{sub c}}}=3665{+-}17{+-}14{sub -78}{sup +0} MeV; the three given uncertainties are statistical, systematic, and an estimate of lattice discretization errors, respectively. In addition, we predict the mass splitting of the (isospin-averaged) spin-1/2 {Omega}{sub cc} with the {Xi}{sub cc} to be M{sub {Omega}{sub c{sub c}}}-M{sub {Xi}{sub c{sub c}}}=98{+-}9{+-}22{+-}13 MeV (in this mass splitting, the leading discretization errors are also suppressed by SU(3) symmetry). Combining this splitting with our determination of M{sub {Xi}{sub c{sub c}}} leads to our prediction of the spin-1/2 {Omega}{sub cc} mass, M{sub {Omega}{sub c{sub c}}}=3763{+-}19{+-}26{sub -79}{sup +13} MeV.

Nucleon structure from mixed action calculations using 2+1 flavors of asqtad sea and domain wall valence fermions

Abstract: United States. Dept. of Energy (Contract No. DE-AC05-06OR23177) (Contract No. DE-FG03-97ER4014)

Lattice Calculations of Nucleon Electromagnetic Form Factors at Large Momentum Transfer

Abstract: In this work, we report a novel technique in lattice QCD for studying the high momentumtransfer region of nucleon form factors. These calculations could give important theoretical input to experiments, such as those of JLab’s 12-GeV program and studies of nucleon deformation. There is an extensive history of form-factor calculations on the lattice, primarily with ground states for both the initial and final state. However, determining form factors at large momentum transfer (Q 2 ) has been difficult due to large statistical and systematic errors in this regime. We study the nucleon form factors using three pion masses with both quenched and 2+1-flavor anisotropic lattice configurations with Q 2 as large as 6 GeV 2 . These form factors are further processed to obtain transverse charge and magnetization densities across 2-dimensional impact-parameter space. Our approach can be applied to isotropic lattices and lattices with smaller lattice spacing to calculate even larger-Q 2 form factors.

Nucleon, Delta and Omega excited state spectra at three pion mass values

Abstract: The energies of the excited states of the Nucleon, D and W are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The calculations are performed at three values of the pion mass: mp = 392(4), 438(3) and 521(3) MeV. We employ the variational method with a basis of about ten interpolating operators enabling six energies to be distinguished clearly in each irreducible representation of the octahedral group. We compare our calculations of nucleon excited states with the low-lying experimental spectrum. There is reasonable agreement for the pattern of states.

Nucleon, Delta and Omega excited state spectra at three pion mass values

Abstract: The energies of the excited states of the Nucleon, Delta and Omega are computed in lattice QCD, using two light quarks and one strange quark on anisotropic lattices. The calculations are performed at three values of the pion mass: 392(4), 438(3) and 521(3) MeV. We employ the variational method with a basis of about ten interpolating operators enabling six energies to be distinguished clearly in each irreducible representation of the octahedral group. We compare our calculations of nucleon excited states with the low-lying experimental spectrum. There is reasonable agreement for the pattern of states.