Showing papers on "Proton spin crisis published in 1988"

Proton spin–lattice relaxation in nematic microdroplets

Abstract: The frequency and temperature dependences of the proton spin–lattice relaxation rate have been studied in nematic droplets embedded in a solid polymer matrix. The comparison of these data to those for bulk nematic and pure polymer samples shows that cross‐relaxation between liquid crystal and polymer protons dominates the liquid crystal relaxation in the MHz frequency region, while at low frequencies the translationally induced molecular rotation becomes important. The cross‐relaxation rate is found to be ≈103 s−1 giving an order of magnitude estimate 10−4–10−3 s for the time for which a liquid crystal molecule is bonded to the surface.

Quark contribution to the proton spin in the chiral quark-meson model

Abstract: It has been argued that, to leading order in the 1/Nc expansion, very little of the spin of the proton is carried by the helicities of its constituent quarks, in accordance with the results of a recent EMC experiment. We investigate this question by a direct computation in the chiral quark-meson model, where the proton spin is generated by cranking a mean field hedgehog baryon. For not too small values of the quark-meson coupling constant, our results are consistent with the EMC data.

Proton spin–lattice relaxation study of a partial bilayer smectic A phase

Abstract: Measurements of proton spin-lattice relaxation rates for the partial bilayer smectic A phase of 4-((4′-n-hexadecyloxybenzylidene)-amino) benzonitrile obtained at different Larmor frequencies and temperatures show that the essential relaxation mechanisms in the MHz frequency region are translational self-diffusion and local molecular reorientations similar to those in monolayer smectics. The values of the diffusion constant obtained from the fit of the theory to the experimental data show a range from 2.6 × 10−11 m2 s−1 at 95°C to 1.7 × 10−11 m2 s−1 at 75°C. A dynamic process specific to the partial bilayer smectic A phase seems to influence relaxation below 10 MHz. It can be associated either with the dimerization of molecules in the layers or with a higher value of the low cut-off frequency of order director fluctuations than that found in monolayer smectic A phases.

Nuclear magnetic resonance in solid ethane at high pressure: III. Proton spin relaxation experiments and molecular motion

Abstract: This article is the last in a series of three papers on an NMR investigation of the effects of hydrostatic pressure up to 10 kbar on the phase transitions and the molecular motion in the three solid phases of ethane. In this paper the experimental results on the spin relaxation times T1 and T2 and on the line shape second moment M2 are presented. In the two ordered solid phases the symmetry and the time scale of the molecular motion is derived by comparing the experimental data with the jump-reorientational model presented in the first paper. In the monoclinic ordered phase III the molecular motions observed are uniaxial 120° jumps about the molecular C3 axis, while in phase II reorientations about the C2 axis become important. In the orientationally disordered phase I, where translational diffusion dominates in the spin-lattice relaxation process, the results are analyzed in terms of an encounter model.

Polarization monitors for proton and deuteron beams below 20 MeV

Abstract: Two polarimeters for proton and deuteron beams using the p+ 4 He scattering and the 3 He(d, p) reaction, respectively, are described. They are placed downstream from a scattering chamber so as to monitor the beam polarization throughout an experiment. Two of the three components of proton spin and six of the eight components of deuteron spin can be measured simultaneously.

Seed proton NMR spin‐grouping

Abstract: Proton spin grouping in the rotating frame allows for a distinction between oil, water and starch protons with a resolution which exceeds the one with the standard proton T1 or T2 oil and water separation experiments. Hence, it has clear advantages in plant breeding programs in those situations where, because of the relatively high oil and water content, the standard NMR technique fails unless the seeds are dried artificially. This technique is just as fast as the standard technique.

Recent EMC results on the spin‐dependent structure function g1 of the proton

Abstract: The NA2’ experiment at CERN has measured the spin asymmetry in deep‐inelastic polarized muon‐proton scattering and extracted the spin‐dependent structure function g1 of the proton The integral of g1 over x was found to be 0114±0012±0026, in disagreement with the Ellis‐Jaffe sum rule An implication is that the quarks account for only a small fraction of the proton spin

Flavor symmetry and the spin of the proton

Abstract: The analysis of the EMC result on the quark contribution to the spin of the proton has been challenged because of the use of SU(3) symmetry is shown not to be needed to obtain peculiar results about these quark contributions. The analysis without assuming flavor symmetry allows the quark contribution to the proton spin to be large, but only if it is due to the strange quarks, with the nonstrange quark contribution opposite to the spin of the proton. Recent data from the European Muon Collaboration have been interpreted to suggest that the spin of the proton does not come from the quarks but from the some other source. This interpretation has been questioned, both because of the errors in extrapolating to x = O and because of the use of flavor SU(3) symmetry to relate spin distributions within the proton to weak semileptonic axial vector decays of hyperons. We consider here the use of flavor symmetry. 3 refs.

Measurements of the order parameter by proton N.M.R. on N-(4-alkoxybenzylidene)4′-toluidines

Abstract: N-(4-alkoxybenzylidene)4′-toluidines are a family of organic compounds which present a nematic and (depending on the chain length) a smectic mesophase. We have performed proton spin echo measurements on some members of the family in these mesophases. N.M.R. spectra present well-defined structures that can be assigned to one of the two end methyl groups on the basis of phenomenological as well as analytical discussion, despite the large number of protons contributing to the total line shape. The order parameter derived from this analysis is compared with optical data on the same compounds.

Spin Dynamics in the Classical Easy-Plane Antiferromagnet Proton Spin-Lattice Relaxation in TMMC

Abstract: A spin wave calculation of the memory function for the classical anisotropic one-dimensional antiferromagnetic Heisenberg model is applied in a calculation of the temperature dependence of the spin–lattice relaxation rate in TMMC [(CH3)4N]MnCl3. Comparison with experiment is made. Eine Spinwellen-Berechnung der Speicherfunktion fur das klassische anisotrope eindimensionale antiferromagnetische Heisenbergmodell wird auf die Berechnung der Temperaturabhangigkeit der Spin–Gitterrelaxationsrate in TMMC[(CH3)4N]MnCl3 angewendet und ein Vergleich mit dem Experiment durchgefuhrt.

Why the proton spin is not due to quarks

Abstract: Recent EMC data on the spin-dependent proton structure function suggest that very little of the proton spin is due to the helicity of the quarks inside it. We argue that, at leading order in the 1/N/sub c/ expansion, none of the proton spin would be carried by quarks in the chiral limit where mq = 0. This model-independent result is based on a physical picture of the nucleon as a soliton solution of the effective chiral Lagrangian of large-N/sub c/ QCD. The Skyrme model is then used to estimate quark contribution to the proton spin when chiral symmetry and flavor SU(3) are broken: this contribution turns out to be small, as suggested by the EMC. Next, we discuss the other possible contributions to the proton helicity in the infinite-momentum frame--polarized gluons (..delta..G), and orbital angular momentum (L/sub z/). We argue on general grounds and by explicit example that ..delta..G = 0 and that if the parameters of the chiral Lagrangian are adjusted so that gluons carry /similar to/50% of the proton momentum, most of the orbital angular momentum L/sub z/ is carried by quarks. We mention several experiments to test the EMC results and their interpretation.