Showing papers on "Proton spin crisis published in 1989"
TL;DR: It is shown that the anomalous divergence equations constrain the size of the gluonic component due to the anomaly in the forward matrix element of the axial-vector current as measured in polarized deep-inelastic electroproduction.
Abstract: Several authors have noted that the forward matrix element of the axial-vector current as measured in polarized deep-inelastic electroproduction represents not only the quark contribution to the target proton spin but also the gluonic component due to the anomaly. We show that the anomalous divergence equations constrain the size of this gluonic contribution. In particular it is of such sign and magnitude that the resulting quark content of the proton spin deviates even further from the naive-quark-model expectations.
65 citations
TL;DR: Carbon-carbon and proton-carbon couplings can be used to bridge the aromatic and aliphatic parts of proton spin systems; this avoids possible ambiguities that may result from the use of nuclear Overhauser effects to assign aromatic amino acid signals.
Abstract: When used in concert, one-bond carbon-carbon correlations, one-bond and multiple-bond proton-carbon correlations, and multiple-bond proton-nitrogen correlations, derived from two-dimensional (2D) NMR spectra of isotopically enriched proteins, provide a reliable method of assigning proton, carbon, and nitrogen resonances. In contrast to procedures that simply extend proton assignments to carbon or nitrogen resonances, this technique assigns proton, carbon, and nitrogen resonances coordinately on the basis of their integrated coupling networks. Redundant spin coupling pathways provide ways of resolving overlaps frequently encountered in homonuclear {sup 1}H 2D NMR spectra and facilitate the elucidation of complex proton spin systems. Carbon-carbon and proton-carbon couplings can be used to bridge the aromatic and aliphatic parts of proton spin systems; this avoids possible ambiguities that may result from the use of nuclear Overhauser effects to assign aromatic amino acid signals. The technique is illustrated for Anabaena 7120 flavodoxin and cytochrome c-553, both uniformly enriched with carbon-13 (26%) or nitrogen-15 (98%).
51 citations
TL;DR: In this paper, the complementary advantages of high sensitivity and high chemical shift dispersion offered by 1H and 13C spins are exploited in experiments designed for indirect observation of the proton system through 13C resonances.
Abstract: The complementary advantages of high sensitivity and high chemical shift dispersion offered by 1H and 13C spins are exploited in experiments designed for indirect observation of the proton system through 13C resonances. Pulse sequences devised for indirect measurements of proton T 2 relaxation times and for indirect observation of proton spin diffusion (an extension of the Goldman-Shen experiment) are presented and compared to direct proton measurements. A proper image of the structural heterogeneity, manifested by three distinct physical regions, is deduced from indirect measurements on static and rotating samples of polyoxymethylene. The results are used as a model for illustrating the potential of the proposed sequences. Possible restrictions on the quantitative analysis of the extent of the different morphological regions are discussed in terms of their different cross-polarization characteristics.
44 citations
TL;DR: In this paper, it was concluded that electronic spin motion is dominated by a quasi-1-D diffusion and the diffusion rate along the chain is almost independent of the protonation rate.
31 citations
TL;DR: In this paper, the Skyrme model predictions for the quark contribution to the proton spin were presented, and an effective operator that corresponds to uγμγ5u+dγμg5d+sγμgam5s was introduced, and its matrix element was calculated in the Proton state in the form Δu+Δd+ Δs = 0.2±0.1.
31 citations
TL;DR: In this article, the authors investigated the strange quark helicity contribution Δs to the spin of the proton in a linear chiral model of quark and gluon confinement, incorporating the effects of SU(3) symmetry breaking.
26 citations
TL;DR: In this paper, a consistent treatment of the abelian axial anomaly in a two-phase model of the proton yields a flavor singlet axial current that is saturated by the anomaly at Q 2 = 0 in the chiral limit.
25 citations
TL;DR: In this article, the quark contributions to the proton spin in a hybrid chiral bag model interpolating between the naive quark model and the Skyrme model were analyzed.
23 citations
TL;DR: In this article, a new approach with a flavor-SU(3) classification only for the weak currents and not for hadron wavefunctions was proposed, which showed that hyperon decay data are essentially useless and do not give model independent information about proton spin distributions.
21 citations
TL;DR: In this paper, the contribution of the proton spin from its gluonic content was investigated by studying the inelastic photoproduction of J/ψ off polarized protons with polarized photons.
20 citations
TL;DR: In this paper, a comparison of the momentum sum rule for the structure function F 2 in unpolarized electroproduction and the spin-sum rule for G 1 in polarized electroproduction was made.
TL;DR: In this article, the proton matrix element of the flavor-singlet axial current (FSAC) is discussed in terms of the chiral bag model with due account of the axial anomaly and quantum number fractionization.
TL;DR: In this paper, the question of whether the constituents of polarized protons are rotating about their polarization axes is discussed and two collision experiments are proposed in which the effects due to rotating constituents should manifest themselves if such orbital motion exists.
Abstract: The question of whether the constituents of polarized protons are rotating about their polarization axes is discussed. Two collision experiments are proposed in which the effects due to rotating constituents should manifest themselves if such orbital motion exists.
TL;DR: The evolution in Q/sup 2/ of the fraction of proton spin carried by gluons depends on the initial spin fractions and it is possible to avoid the introduction of large orbital angular momentum by adopting a ''hybrid'' quark-Skyrme picture of the proton suggested by the EMC results.
Abstract: New data from the European Muon Collaboration (EMC) on the spin-spin asymmetry in deep-inelastic lepton-proton scattering suggests that the total spin carried by valence quarks in a polarized proton may be approximately canceled by a strong negative polarization of the sea of q-barq pairs. The evolution in Q/sup 2/ of the fraction of proton spin carried by gluons depends on the initial spin fractions and it is possible to avoid the introduction of large orbital angular momentum by adopting a ''hybrid'' quark-Skyrme picture of the proton suggested by the EMC results.
TL;DR: In this paper, the Hartree-Fock wave function was used to calculate the carbon-proton 1 J and protonproton 2 J spin-spin coupling surfaces for the methane molecule.
Abstract: Carbon-proton 1 J and proton-proton 2 J spin-spin coupling surfaces for the methane molecule have been calculated using a Hartree-Fock wavefunction. The dependences of all four contributions—Fermi contact, spin-dipolar, orbital paramagnetic and orbital diamagnetic—upon a set of four internal symmetry coordinates are presented. All first order derivatives and many of the second order derivatives of both surfaces have been obtained. The principal feature of the results is the very great dependence of the magnitudes (and often the signs) of the contributions upon the molecular geometry.
TL;DR: In this paper, the suppression of nonsinglet axial vector couplings gA/gV from the naive quark model value can easily be understood as an effect of the mesonic cloud around the proton.
CERN1
TL;DR: In this paper, it was shown that a large part of the proton spin is carried by gluons and the gluon component can be determined by a measurement of the polarized structure functions at very high energies.
TL;DR: In this paper, the structure of non-strange baryons is investigated in a field-theoretical model which minimally incorporates soft confinement of quarks and gluons and approximate chiral symmetry.
TL;DR: This work analyzes the recent European Muon Collaboration data on the proton spin asymmetry in a relativistic constituent-quark model of the nucleon and estimates the size of orbital angular momentum carried by the valence constituents.
Abstract: We analyze the recent European Muon Collaboration (EMC) data on the proton spin asymmetry in a relativistic constituent-quark model of the nucleon. In a convolution approach we calculate the /ital x/ dependence of the spin-weighted and spin-averaged quark distributions. We estimate the size of orbital angular momentum carried by the valence constituents, , to be sizable (about 20--25 % of the proton spin). This depletes the valence-quark contribution to the proton spin, but not enough to account for the spin deficit claimed by the EMC.
TL;DR: In this paper, Proton NMR has been studied between 0.01 and 1 K in various hydrates of CaSO 4 as part of a program to investigate spin-lattice relaxation mechanisms at low temperatures.
TL;DR: In this paper, the mean flip-flop time of proton spin diffusion in solid-state samples can be directly measured by using depolarization of rare spins in CP MAS NMR.
TL;DR: Measurement of the spin carried by the quarks in the proton can be very important in distinguishing between low-energy models of the hadron.
Abstract: Measurement of the spin carried by the quarks in the proton can be very important in distinguishing between low-energy models of the hadron. Topological soliton models have rather little or no spin in the quarks, in agreement with present experimental indications.
TL;DR: In this article, the authors compute the nonstrange quark contribution Δu+Δd to the proton spin in a chiral field-theoretical model of quark and gluon confinement.
TL;DR: In this article, structural properties of isotactic polypropylene film during stretching were investigated mainly by the measurements of proton spin-lattice, T1 and spin-spin, T2, relaxation times.
Abstract: Structural properties of isotactic polypropylene film during stretching were investigated mainly by the measurements of proton spin-lattice, T1 and spin-spin, T2, relaxation times. Both T1 and T2a, T2 of the most mobile amorphous regions, of the sample stretched at 150°C are longer than those of the sample stretched at 130°C. These results indicate that in the sample stretched at 150°C the proportion of mobile amorphous region decreases, while the amorphous region achieves enhanced molecular mobility.
TL;DR: In this paper, the proton spin-lattice relaxation times were measured for HDO in the dipalmitoylphosphatidylcholine-D 2 O system at fine temperature intervals.
TL;DR: In this article, the effects of nonspecific solute-solvent interactions on the directly bonded carbon-proton couplings in acetaldehyde, acetone and acrylonitrile were investigated.
Abstract: A theoretical study of the effects of non-specific solute-solvent interactions on the directly bonded carbon-proton couplings1
J(C–H), in acetaldehyde, acetone and acrylonitrile is presented. The solvent induced changes in these couplings calculated by an INDO-SCPT procedure incorporating a modified solvaton model are in satisfactory agreement with experiment and show significant improvement over the INDO-FPT calculations using the Klopman-Germer solvaton model.
TL;DR: The MLEV‐17 proton spin locking pulse is applied to 1H‐31P 2D heteronuclear correlation spectroscopy and the 3′‐, 4′‐ and 5′‐proton resonances can be traced ‘sequentially’ along the chain on the 2D NMR chart.