Showing papers by "Huey-Wen Lin published in 2015"

Flavor structure of the nucleon sea from lattice QCD

Abstract: We present the first direct lattice calculation of the isovector sea-quark distributions in the nucleon within the framework of the large-momentum effective field theory proposed recently. We use ${N}_{f}=2+1+1$ highly improved staggered quarks lattice gauge ensembles (generated by the MILC Collaboration) and clover valence fermions with pion mass 310 MeV. We establish the convergence of the result as the nucleon momentum increases within the uncertainty of the calculation. Although the lattice systematics are not yet fully under control, we obtain some qualitative features of the flavor structure of the nucleon sea: $\overline{d}(x)g\overline{u}(x)$ leading to the violation of the Gottfried sum rule, $\mathrm{\ensuremath{\Delta}}\overline{u}(x)g\mathrm{\ensuremath{\Delta}}\overline{d}(x)$ as indicated by the STAR data at large and small leptonic pseudorapidity.

Neutron Electric Dipole Moment and Tensor Charges from Lattice QCD

Abstract: We present lattice QCD results on the neutron tensor charges including, for the first time, a simultaneous extrapolation in the lattice spacing, volume, and light quark masses to the physical point in the continuum limit. We find that the "disconnected" contribution is smaller than the statistical error in the "connected" contribution. Our estimates in the modified minimal subtraction scheme at 2 GeV, including all systematics, are g_{T}^{d-u}=1.020(76), g_{T}^{d}=0.774(66), g_{T}^{u}=-0.233(28), and g_{T}^{s}=0.008(9). The flavor diagonal charges determine the size of the neutron electric dipole moment (EDM) induced by quark EDMs that are generated in many new scenarios of CP violation beyond the standard model. We use our results to derive model-independent bounds on the EDMs of light quarks and update the EDM phenomenology in split supersymmetry with gaugino mass unification, finding a stringent upper bound of d_{n}<4×10^{-28} e cm for the neutron EDM in this scenario.

Isovector and Isoscalar Tensor Charges of the Nucleon from Lattice QCD

Abstract: We present results for the isovector and flavor diagonal tensor charges ${g}_{T}^{u\ensuremath{-}d}$, ${g}_{T}^{u}$, ${g}_{T}^{d}$, and ${g}_{T}^{s}$ needed to probe novel tensor interactions at the TeV scale in neutron and nuclear $\ensuremath{\beta}$-decays and the contribution of the quark electric dipole moment (EDM) to the neutron EDM. The lattice QCD calculations were done using nine ensembles of gauge configurations generated by the MILC collaboration using the HISQ action with $2+1+1$ dynamical flavors. These ensembles span three lattice spacings $a\ensuremath{\approx}0.06$, 0.09 and 0.12 fm and three quark masses corresponding to the pion masses ${M}_{\ensuremath{\pi}}\ensuremath{\approx}130$, 220 and 310 MeV. Using estimates from these ensembles, we quantify all systematic uncertainties and perform a simultaneous extrapolation in the lattice spacing, volume and light quark masses for the connected contributions. The final estimates of the connected nucleon (proton) tensor charge for the isovector combination is ${g}_{T}^{u\ensuremath{-}d}=1.020(76)$ in the $\overline{\mathrm{MS}}$ scheme at 2 GeV. The additional disconnected quark loop contributions needed for the flavor-diagonal matrix elements are calculated using a stochastic estimator employing the truncated solver method with the all-mode-averaging technique. We find that the size of the disconnected contribution is smaller than the statistical error in the connected contribution. This allows us to bound the disconnected contribution and include it as an additional uncertainty in the flavor-diagonal charges. After a continuum extrapolation, we find ${g}_{T}^{u}=0.774(66)$, ${g}_{T}^{d}=\ensuremath{-}0.233(28)$ and ${g}_{T}^{u+d}=0.541(67)$. The strangeness tensor charge, that can make a significant contribution to the neutron EDM due to the large ratio ${m}_{s}/{m}_{u,d}$, is ${g}_{T}^{s}=0.008(9)$ in the continuum limit.

Lattice study of quark and glue momenta and angular momenta in the nucleon

Abstract: We report a complete calculation of the quark and glue momenta and angular momenta in the proton. These include the quark contributions from both the connected and disconnected insertions. The quark disconnected insertion loops are computed with ${Z}_{4}$ noise, and the signal-to-noise ratio is improved with unbiased subtractions. The glue operator is comprised of gauge-field tensors constructed from the overlap operator. The calculation is carried out on a $1{6}^{3}\ifmmode\times\else\texttimes\fi{}24$ quenched lattice at $\ensuremath{\beta}=6.0$ for Wilson fermions with $\ensuremath{\kappa}=0.154$, 0.155, and 0.1555, which correspond to pion masses at 650, 538, and 478 MeV, respectively. The chirally extrapolated $u$ and $d$ quark momentum/angular momentum fraction is found to be $0.64(5)/0.70(5)$, the strange momentum/angular momentum fraction is $0.024(6)/0.023(7)$, and that of the glue is $0.33(6)/0.28(8)$. The previous study of quark spin on the same lattice revealed that it carries a fraction of 0.25(12) of proton spin. The orbital angular momenta of the quarks are then obtained from subtracting the spin from their corresponding angular momentum components. We find that the quark orbital angular momentum constitutes 0.47(13) of the proton spin with almost all of it coming from the disconnected insertions.

Quarkonium-nucleus bound states from lattice QCD

Abstract: Quarkonium-nucleus systems are composed of two interacting hadronic states without common valence quarks, which interact primarily through multi-gluon exchanges, realizing a color van der Waals force. We present lattice QCD calculations of the interactions of strange and charm quarkonia with light nuclei. Both the strangeonium-nucleus and charmonium-nucleus systems are found to be relatively deeply bound when the masses of the three light quarks are set equal to that of the physical strange quark. Extrapolation of these results to the physical light-quark masses suggests that the binding energy of charmonium to nuclear matter is B < 40 MeV.

Lattice QCD for nuclear physics

Abstract: Lattice QCD: a Brief Introduction.- Lattice Methods for Hadron Spectroscopy.- Hadron Structure on the Lattice.- Chiral Perturbation Theory.- Nuclear Physics From Lattice QCD.- High Temperature and Density in Lattice QCD.- References.

Quarkonium-nucleus bound states from lattice QCD

Abstract: Dept. d’Estructura i Constituents de la Materia. Institut de Ciencies del Cosmos (ICC),Universitat de Barcelona, Mart Franques 1, E08028-Spain(Dated: October 30, 2014)Quarkonium-nucleus systems are composed of two interacting hadronic states without commonvalence quarks, which interact primarily through multi-gluon exchanges, realizing a color van derWaals force. We present lattice QCD calculations of the interactions of strange and charm quarkoniawith light nuclei. Both the strangeonium-nucleus and charmonium-nucleus systems are found to berelatively deeply bound when the masses of the three light quarks are set equal to that of the physicalstrange quark. Extrapolation of these results to the physical light-quark masses suggests that thebinding energy of charmonium to nuclear matter is B

Bjorken-x Dependence of Hadronic Structure from Lattice QCD

Abstract: I present a first direct lattice-QCD calculation of the Bjorken-x dependence of hadron structure functions. By taking a hadron with a large momentum boost, we are able to connect light-cone quantities to lattice-QCD nonlocal but time-independent matrix elements. Since the largest attainable momentum is limited, we correct for the sizable leading momentum dependence systematically. In this talk, I present an exploratory study of the nucleon quark density, helicity and transversity distributions.

Precision calculations of nucleon charges $g_A$, $g_S$, $g_T$

Abstract: We present a detailed analysis of statistical and systematic errors in the calculation of matrix elements of iso-vector scalar, axial and tensor charges between a neutron and a proton state. These analyses are being done on dynamical $N_f=2+1+1$ HISQ configurations generated by the MILC Collaboration using valence clover fermions. Using ensembles at three values of the lattice spacing ($a=0.12,\ 0.09,$ and $0.06$ fm) and three values of the quark mass ($M_\pi \approx 310,\ 220$ and $130$ MeV) we find that the estimates of the tensor charge are stable and it can be extracted with $5\%$ precision with O(10,000) measurements. We also find that higher statistics are needed to resolve the various uncertainties in the calculation of $g_A$ and improve the signal in $g_S$, which with present data has large errors. A brief status report on the mixing and renormalization of novel operators contributing to nEDM is also given.

Precision calculations of nucleon charges $g_A$, $g_S$, $g_T$

Abstract: We present a detailed analysis of statistical and systematic errors in the calculation of matrix elements of iso-vector scalar, axial and tensor charges between a neutron and a proton state. These analyses are being done on dynamical $N_f=2+1+1$ HISQ configurations generated by the MILC Collaboration using valence clover fermions. Using ensembles at three values of the lattice spacing ($a=0.12,\ 0.09,$ and $0.06$ fm) and three values of the quark mass ($M_\pi \approx 310,\ 220$ and $130$ MeV) we find that the estimates of the tensor charge are stable and it can be extracted with $5\%$ precision with O(10,000) measurements. We also find that higher statistics are needed to resolve the various uncertainties in the calculation of $g_A$ and improve the signal in $g_S$, which with present data has large errors. A brief status report on the mixing and renormalization of novel operators contributing to nEDM is also given.