5,934 research outputs found

    Latest Results on g1g_1 and g2g_2 at high xx

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    Recent progress from Jefferson Lab has significantly improved our understanding of the nucleon spin structure in the high-xx region. Results of a precision measurement of the neutron spin asymmetry, A1nA_1^n, in the high-xx (valence quark) region are discussed. The up and down quark spin distributions in the nucleon were extracted. A2nA_2^n was also measured. The results were used, in combination with existing data, to extract the second moment, d2nd_2^n. Preliminary results on A1pA_1^p and A1dA_1^d in the high-xx region have also become available. Finally, the results of a precision measurement of the g2g_2 structure function to study higher twist effects will be presented.Comment: 4 pages, 2 figures, to appear in the DIS2005 Proceedings (AIP

    Spin Sum Rules at Low Q2Q^2

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    Recent precision spin-structure data from Jefferson Lab have significantly advanced our knowledge of nucleon structure at low Q2Q^2. Results on the neutron spin sum rules and polarizabilities in the low to intermediate Q2Q^2 region are presented. The Burkhardt-Cuttingham Sum Rule was verified within experimental uncertainties. When comparing with theoretical calculations, results on spin polarizability show surprising disagreements with Chiral Perturbation Theory predictions. Preliminary results on first moments at very low Q2Q^2 are also presented.Comment: 4 pages, to be published in the Proceedings of the 10th Conference on Intersections of Nuclear and Particle Physics (CIPANP

    The consistency of estimator under fixed design regression model with NQD errors

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    In this article, basing on NQD samples, we investigate the fixed design nonparametric regression model, where the errors are pairwise NQD random errors, with fixed design points, and an unknown function. Nonparametric weighted estimator will be introduced and its consistency is studied. As special case, the consistency result for weighted kernel estimators of the model is obtained. This extends the earlier work on independent random and dependent random errors to NQD case

    Flux-lattice melting in LaO1x_{1-x}Fx_{x}FeAs: first-principles prediction

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    We report the theoretical study of the flux-lattice melting in the novel iron-based superconductor LaO0.9F0.1FeAsLaO_{0.9}F_{0.1}FeAs and LaO0.925F0.075FeAsLaO_{0.925}F_{0.075}FeAs. Using the Hypernetted-Chain closure and an efficient algorithm, we calculate the two-dimensional one-component plasma pair distribution functions, static structure factors and direct correlation functions at various temperatures. The Hansen-Verlet freezing criterion is shown to be valid for vortex-liquid freezing in type-II superconductors. Flux-lattice meting lines for LaO0.9F0.1FeAsLaO_{0.9}F_{0.1}FeAs and LaO0.925F0.075FeAsLaO_{0.925}F_{0.075}FeAs are predicted through the combination of the density functional theory and the mean-field substrate approach.Comment: 5 pages, 4 figures, to appear in Phys. Rev.

    Spin Sum Rules and Polarizabilities

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    The Gerasimov-Drell-Hearn sum rule and related dispersive integrals connect real and virtual Compton scattering to inclusive photo- and electroproduction. Being based on universal principles as causality, unitarity, and gauge invariance, these relations provide a unique testing ground to study the internal degrees of freedom that hold a system together. The present contribution reviews the spin-dependent sum rules and cross sections of the nucleon. At small momentum transfer, the data sample information on the long range phenomena (Goldstone bosons and collective resonances), whereas the primary degrees of freedom (quarks and gluons) become visible at large momentum transfer (short distance). The rich body of new data covers a wide range of phenomena from coherent to incoherent processes, and from the generalized spin polarizabilities on the low-energy side to higher twist effects in deep inelastic scattering.Comment: 15 pages, 7 figures, Proc. of Spin structure at long distance, Newport News, Virginia, 200