We present high statistics results for the isovector charges g u−dA , g u−dS and g u−dT of the nucleon. Calculations were carried out on eleven ensembles of gauge configurations generated by the MILC collaboration using highly improved staggered quarks action with 2 þ 1 þ 1 dynamical flavors. These ensembles span four lattice spacings a ≈ 0.06, 0.09, 0.12 and 0.15 fm and light-quark masses corresponding to M π ≈ 135, 225 and 315 MeV. Excited-state contamination in the nucleon three-point correlation functions is controlled by including up to three-states in the spectral decomposition. Remaining systematic uncertainties associated with lattice discretization, lattice volume and light-quark masses are controlled using a simultaneous fit in these three variables. Our final estimates of the isovector charges in the MS scheme at 2 GeV are T with precision low-energy nuclear experiments, and find them comparable to those from the ATLAS and the CMS experiments at the LHC.
We present results for the isovector axial, scalar and tensor charges g 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 ≈ 0.06, 0.09 and 0.12 fm and light-quark masses corresponding to the pion masses Mπ ≈ 135, 225 and 315 MeV. High-statistics estimates on five ensembles using the all-mode-averaging method allow us to quantify all systematic uncertainties and perform a simultaneous extrapolation in the lattice spacing, lattice volume and light-quark masses for the connected contributions. Our final estimates, in the MS scheme at 2 GeV, of the isovector charges are g (51)(20). The first error includes statistical and all systematic uncertainties except that due to the extrapolation Ansatz, which is given by the second error estimate. Combining our estimate for g 194(14). Combining our new estimates with precision low-energy experiments, we present updated constraints on novel scalar and tensor interactions, S,T , at the TeV scale.
We present results for the isovector and flavor diagonal tensor charges g needed to probe novel tensor interactions at the TeV scale in neutron and nuclear β-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 ≈ 0.06, 0.09 and 0.12 fm and three quark masses corresponding to the pion masses Mπ ≈ 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 u−d T = 1.020(76) in the 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
We present lattice-QCD results on the nucleon isovector axial, scalar and tensor charges, the isovector electromagnetic Dirac and Pauli form factors, and the connected parts of the isoscalar charges. The calculations have been done using two ensembles of HISQ lattices generated by the MILC Collaboration with 2+1+1 dynamical flavors at a lattice spacing of 0.12 fm and with lightquark masses corresponding to pions with masses 310 and 220 MeV. We perform a systematic study including excited-state degrees of freedom and examine the dependence of the extracted nucleon matrix elements on source-sink separation. This study demonstrates with high-statistics data that including excited-state contributions and generating data at multiple separations is necessary to remove contamination that would otherwise lead to systematic error. We also determine the renormalization constants of the associated quark bilinear operators in the RI-sMOM scheme and make comparisons of our renormalized results with previous dynamical-lattice calculations.
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 MS scheme at 2 GeV, including all systematics, are g . 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 (BSM). 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 dn < 4 × 10 −28 e cm for the neutron EDM in this scenario. , one needs to accurately calculate matrix elements of appropriate low-energy effective operators within neutron states. In this paper we describe lattice QCD calculations of the neutron tensor charges. In the future, these charges will be extracted with competitive precision from various measurements of the quark transversity distributions at JLab [2], and provide robust tests of the lattice results.The flavor diagonal charges g u,d,s T are needed to quantify the contribution of the quark EDM to the neutron EDM and thus set bounds on BSM sources of CP violation. We find that the contribution of the "disconnected" diagrams to g is needed in the analysis of precision neutron β-decay. In Ref.[3] we showed that to complement experimental measurements of the helicity flip contributions to neutron β-decay at the precision of planned experiments (10 −3 level), we need to calculate the iso-vector scalar and tensor charges, g Table I. On these ensembles, we construct correlation functions using Wilson-clover fermions, as these preserve the continuum spin structure. To reduce short-distance noise, all lattices were "HYP" smeared [7]. Extensive tests were carried out on these nine HYP smeared ensembles to look for the presence of exceptional configurations The zero-momentum projection of χ(x) couples to the ground state, all radially excited states of the neutron, and multiparticle states. To reduce the coupling to radially excited states we Gaussian smear the quark fields in χ(x). To isolate the remaining excited state contamination, we include two states in the analysis of the two-and three-point functions at zero momentum [4]. Even though the excited state contribution is exponentially suppressed, we were able to isolate the leading two unwanted matrix elements 0|O Γ |1 and 1|O Γ |1 , where |0 and |1 represent the ground and first excited neutron states. We find that the magnitude of 0|O Γ |1 is about 16% of 0|O Γ |0 and is determined with about 20% uncertainty on all the ensembles, whereas arXiv:1506.04196v4 [hep-lat]
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