A lattice study of the strangeness content of the nucleon (original) (raw)

Lattice calculation of the strangeness magnetic moment of the nucleon

Physical Review D, 1998

We report on a lattice QCD calculation of the strangeness magnetic moment of the nucleon. Our result is G s M (0) = −0.36 ± 0.20. The sea contributions from the u and d quarks are about 80% larger. However, they cancel to a large extent due to their electric charges, resulting in a smaller net sea contribution of −0.097 ± 0.037µ N to the nucleon magnetic moment. As far as the neutron to proton magnetic moment ratio is concerned, this sea contribution tends to cancel out the cloud-quark effect from the Z-graphs and result in a ratio of −0.68 ± 0.04 which is close to the SU(6) relation and the experiment. The strangeness Sachs electric mean-square radius r 2 s E is found to be small and negative and the total sea contributes substantially to the neutron electric form factor.

Strangeness content and structure function of the nucleon in a statistical quark model

European Physical Journal C, 1999

The strangeness content of the nucleon is determined from a statistical model using confined quark levels, and is shown to have a good agreement with the corresponding values extracted from experimental data. The quark levels are generated in a Dirac equation that uses a linear confining potential (scalar plus vector). With the requirement that the result for the Gottfried sum rule violation, given by the New Muon Collaboration (NMC), is well reproduced, we also obtain the difference between the structure functions of the proton and neutron, and the corresponding sea quark contributions.

Improved method for calculating nucleon strangeness

2010

The strange quark content of the nucleon, as well as other matrix elements, can be calculated on the lattice by examining correlations between the nucleon propagator and the quark condensate. The largest contribution to statistical error comes from fluctuations in the condensate far from the propagation region that contribute only noise. We will report on a technique for considering only the condensate near the propagation region, significantly reducing the statistical error.

Strangeness content in the nucleon

Journal of Physics G: Nuclear and Particle Physics, 2001

I will review recent studies of strangeness content in the nucleon pertaining to the flavor-singlet g 0 A , thess matrix element and the strangeness electric and magnetic form factors G s E (q 2) and G s M (q 2), based on lattice QCD calculations. I shall also discuss the relevance of incorporating the strangeness content in nuclei in regard to strange baryon-antibaryon productions from protonnucleus and nucleus-nucleus collisions at SPS and RHIC energies.

Flavor structure of the nucleon sea from lattice QCD

Physical Review D, 2015

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 HISQ lattice gauge ensembles (generated by 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 : d(x) > u(x) leading to the violation of the Gottfried sum rule; ∆u(x) > ∆d(x) as indicated by the STAR data at large and small leptonic pseudorapidity.

Strangeness matrix elements in the nucleon

Physics Letters B, 1992

We investigate the strangeness "content" of the proton in three nucleonic models: a simple relativistic meson-loop picture, a naive nonrelativistic quark model with mesons, and an extended cloudy bag model. In each case, pseudoscalar mesons are included. Nucleon matrix elements involving strange quarks are generated through the formation of a kaon cloud. We concentrate on the last two models, with the one free parameter chosen to reproduce the electromagnetic nucleon observables. We give theoretical predictions for F~(0), the strange quark contribution to the weak magnetic form factor, (r2)s, the strangeness radius of the nucleon, and g~, the strangeness axial vector matrix element. We observe a strong dependence of the strange quark matrix elements on the choice of the momentum cutoff or bag size.

Form factors and other measures of strangeness in the nucleon

Physical Review D, 2008

We discuss the phenomenology of strange-quark dynamics in the nucleon, based on experimental and theoretical results for electroweak form factors and for parton densities. In particular, we construct a model for the generalized parton distribution that relates the asymmetry s(x) −s(x) between the longitudinal momentum distributions of strange quarks and antiquarks with the form factor F s 1 (t), which describes the distribution of strangeness in transverse position space.

Polarisation of valence and non-strange sea quarks in the nucleon from semi-inclusive spin …

Physics Letters B

We present a measurement of semi-inclusive spin asymmetries for positively and negatively charged hadrons from deep inelastic scattering of polarised muons on polarised protons and deuterons in the range 0:003 < x < 0 : 7. From these asymmetries and the previously published inclusive spin asymmetries we determine, for the rst time, the x-dependent spin distributions for up and down valence quarks and for non-strange sea quarks. We nd that the rst moments of the valence quark spin distributions are u v = 1 : 01 0:19 0:14 and d v = 0:57 0:22 0:11. The spin distribution function of non-strange sea quarks is consistent with zero over the measured range of x and the rst moment i s u = d = 0 : 02 0:09 0:03.

Strangeness and glue in the nucleon from lattice QCD

2008

We study the strangeness contribution to nucleon matrix elements using N f = 2 + 1 dynamical clover fermion configurations generated by the CP-PACS/JLQCD collaboration. In order to evaluate the disconnected insertion (DI), we use the Z(4) stochastic method, along with unbiased subtraction from the hopping parameter expansion which reduces the off-diagonal noises in the stochastic method. Furthermore, we find that using many nucleon sources for each configuration is effective in improving the signal. Our results for the quark contribution to the first moment x q in the DI, and the strangeness magnetic moment show that the statistical errors are under control with these techniques. We also study the gluonic contribution to the nucleon using the overlap operator to construct the gauge field tensor, F µν . The application to the calculation of first moment, x G , gives a good signal in quenched lattice QCD.