Showing papers on "Proton spin crisis published in 1993"
TL;DR: A review of various approaches to the problem of the proton spin is presented in this article, where arguments are given in favor of the idea that the answer to the spin crisis is to be found in fundamental nonperturbative properties of the QCD vacuum.
Abstract: A review of various approaches to the problem of the proton spin is presented. Arguments are given in favor of the idea that the answer to the “spin crisis” is to be found in fundamental nonperturbative properties of the QCD vacuum.
56 citations
TL;DR: In this article, it was shown that in both the gluonic and strange sea explanations of the Ellis-Jaffe sum rule violation discovered by the European Muon Collaboration (EMC), the spin of the proton, when viewed in its rest reference frame, could be fully provided by quarks and antiquarks within a simple quark model picture, taken into account the relativistic effect from the Wigner rotation.
Abstract: It is shown that in both the gluonic and strange sea explanations of the Ellis-Jaffe sum rule violation discovered by the European Muon Collaboration (EMC), the spin of the proton, when viewed in its rest reference frame, could be fully provided by quarks and antiquarks within a simple quark model picture, taken into account the relativistic effect from the Wigner rotation.
49 citations
TL;DR: A method is described for investigating local proton "spin diffusion" by means of a 13C spin probe and the spin-diffusion rate constant is found to be proportional to the spinning speed in the range from 1 to 8 kHz.
36 citations
TL;DR: In this article, a reinterpretation of the experimental NMR proton spin-lattice dispersion curve of the Ni2+(H2O)6 complex is presented within a general slow-motion theory.
Abstract: A reinterpretation of the experimental NMR proton spin-lattice dispersion curve of the Ni2+(H2O)6 complex is presented within a general slow-motion theory. The extended pseudo rotation (PR) model developed allows for cross-correlation effects between the nuclear spin-electron spin dipole-dipole and zero field splitting (ZFS) interaction. It is shown that the decomposition approach, treating the electron spin relaxation and the reorientational dynamic of the dipole-dipole correlation function as independent processes is not generally valid. For the Ni-hexa-aquo complex the transient ZFS interaction and the reorientational correlation time change by about 20 per cent due to the correlation effects. Molecular dynamics (MD) simulation of a divalent ion in water provided the timescale of the dynamics present in the PR and the Smoluchowsky models. The structure and dynamics of the octahedral complex is described. The transient ZFS interaction generated by the low frequency vibration modes n(M ↔ OH2) is characte...
26 citations
TL;DR: In this paper, the experimental results were analyzed to obtain the electronic (Korringa) contributions to the relaxation rates and the parameters of hydrogen motion, and the average activation energies for hydrogen diffusion in ZrCr2Hx (81 and 84 meV for x=0.2 and 0.5, respectively) were lower than in the other studied hydrides of intermetallic compounds.
Abstract: Nuclear magnetic resonance (NMR) measurements of the proton spin-lattice relaxation times in the C15-type compounds ZrCr2Hx (x=0.2 and 0.5) have been performed over the temperature range 11-440 K. The experimental results are analysed to obtain the electronic (Korringa) contributions to the relaxation rates and the parameters of hydrogen motion. For both samples hydrogen is found to retain high mobility on the NMR frequency scale down to 78 K. The average activation energies for hydrogen diffusion in ZrCr2Hx (81 and 84 meV for x=0.2 and 0.5, respectively) are lower than in the other studied hydrides of intermetallic compounds.
26 citations
TL;DR: In this article, NMR field-cycling measurements of the deuteron spin relaxation dispersion for the fully deuteriated nematic liquid crystal 4n-pentyl-4′-cyanobiphenyl (5CB-d 19) over a broader Larmor frequency range (v≈10 kHz to 30 MHz) than reported so far in the literature basically confirm the magnetic relaxation mechanisms previously observed by frequency dependent proton spin studies of various nematogenic molecules.
Abstract: NMR field-cycling measurements of the deuteron spin relaxation dispersion T 1(v) for the fully deuteriated nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl (5CB-d 19) over a broader Larmor frequency range (v≈10 kHz to 30 MHz) than reported so far in the literature basically confirm the magnetic relaxation mechanisms previously observed by frequency dependent proton spin studies of various nematogenic molecules, namely collective nematic modes of the director field in the kilohertz regime, and anisotropic reorientations of individual molecules (mainly self-diffusion for the protons and mainly rotations about the long axis for the deuterons) in the megahertz range. Within the experimental error limits such a model allows a self-consistent interpretation of the available deuteron and proton T 1(v) results for deuteriated or protonated 5CB, respectively. In particular, the magnitudes of the measured order fluctuation contributions are in approximate accordance, i.e. within a factor of less than two...
24 citations
TL;DR: In this article, the authors deal with the complete interpretation of the HOESY two dimensional nuclear magnetic resonance (NMR) experiment, aiming at the determination of cross relaxation rates between two different nuclear species, here proton and carbon 13.
Abstract: This paper deals with the complete interpretation of the heteronuclear Overhauser effect spectroscopy (HOESY) two dimensional nuclear magnetic resonance (NMR) experiment. This experiment aims at the determination of cross relaxation rates (having their origin in dipolar interactions) between two different nuclear species, here proton and carbon‐13. Extra correlation peaks observed in the 2D map of the system under investigation (micellized sodium octanoate) are shown to arise from remote dipolar interactions and not from strong (J) coupling effects. Several experiments have been performed at different mixing times (during which the nuclear Overhauser effect builds up), allowing the observation of the whole carbon‐13 magnetization evolution. Their analysis yields cross‐relaxation rates, refined with respect to those derived from initial behavior. However, this requires inclusion of the effect of spin diffusion, within the proton spin system, in the data treatment. A novel approach is proposed which models ...
18 citations
TL;DR: In this article, the authors studied the time and temperature dependence of spin conversion in rotational tunneling molecules and showed that a change in neutron scattering cross section after a rapid change in lattice temperature is the unequivocal signature of spin species conversion.
Abstract: The total proton spin of rotational tunneling molecules like CH3, NH3 or NH4+ groups has a strong influence on the total incoherent scattering cross section of long wavelength neutrons. At sufficiently low temperatures, a change in neutron scattering cross section after a rapid change in lattice temperature is the unequivocal signature of spin species conversion. This effect is used to study the time and temperature dependence of spin conversion. In a simple transmission experiment, we have screened 30 candidate substances of which 13 did not convert on a timescale of days. The other 17 converted: 10 contain paramagnetic ions and their spin temperature follows quasi instantaneously the lattice temperature. Seven substances convert slowly on a time scale of hours. Experimental results are presented and the advantages and limitations of the method are discussed.
14 citations
TL;DR: In this article, the relative spin structure of the nucleon generated by soft mesonic radiative corrections is studied within the light-cone perturbation theory, and the axial-vector current matrix elements are shown to receive large corrections from beyond the conventional static limit.
Abstract: Peripheral spin structure of the nucleon generated by the soft mesonic radiative corrections is studied within the light-cone perturbation theory. Starting with the tree-levelSU (6) symmetry, we find good description of the axial-vector couplings in β-decay of hyperons. We study the proton helicity flow from the baryonic core to the angular momentum of the pionic cloud. It is found that in the relativistic light-cone approach the spin-flip pattern is different from that in the conventional nonrelativistic models. The axial-vector current matrix elements are shown to receive large corrections from beyond the conventional static limit. The important virtue of using the light-cone vertex functions of the meson-baryon Fock components of the proton is that the local gauge invariance and the energy-momentum sum rule are satisfied automatically. We infer the radius of the light-cone form factor from an analysis of the experimental data on the fragmentation of high-energy protons into nucleons and hyperons-the process dominated by stripping off the mesons of the meson-baryon Fock states.
13 citations
TL;DR: An experimental value for the g-factor of the 7 2 proton was derived from the measured magnetic moment of the 141+ state in 214Ra (nominal configuration |( h 9 2 5 21 2 f 7 2 ; 14 + 〉) using the multiparticle octupole-coupling model.
9 citations
TL;DR: In this article, the temperature dependence of the solid-state proton Zeeman relaxation rate in polycrystalline 1,2,4,5-tetraisopropylbenzene has been measured at Larmor frequencies of 8.5 and 53 MHz.
Abstract: The temperature dependence of the solid-state proton Zeeman relaxation rate in polycrystalline 1,2,4,5-tetraisopropylbenzene has been measured at Larmor frequencies of 8.5 and 53 MHz. The isopropyl groups are immobile on the NMR timescale. The data are interpreted with a very small distribution of barriers for all eight methyl groups and this is consistent with a molecular geometry which has the isopropyl lone protons in neighbouring pairs, facing each other in the plane of the aromatic ring. It was also possible to interpret the data with a two-site model consistent with the much less sterically hindered arrangement whereby the isopropyl group lone protons are rotated by ca. 45° in opposite directions out of the plane of the ring. These matters are discussed and the models are compared with results from other spectroscopic measurements. This and other isopropyl systems are compared with related ethyl and tert-butyl systems. Also, the observation of non-exponential nuclear spin relaxation is discussed.
TL;DR: In this paper, the authors used both conventional and fast field cycling NMR techniques to obtain the T 1 dispersion curves at two different temperatures for each mesophase covering frequencies from 102 to 3 × 108 Hz.
Abstract: Proton spin-lattice relaxation studies were carried out in the SA and S*C phases of the liquid crystal CI IPNOC using both conventional and fast field cycling NMR techniques. T 1 dispersion curves were obtained at two different temperatures for each mesophase covering frequencies from 102 to 3 × 108 Hz. In both mesophases the T 1 data can be described assuming the presence of three different relaxation mechanisms, namely local molecular rotations, molecular self-diffusion and collective motions. The self-diffusion constant D 1 was evaluated for several temperatures and the activation energy associated with the diffusion process was obtained. The expected contribution of the soft-mode for the spin-lattice relaxation could not be separated from the contribution of other collective motions. The correlation times associated with the rotations around the molecular long axis and with the fluctuations of this axis were evaluated for both the SA and the S*C phases.
TL;DR: In this paper, a systematic analysis of different processes with high energy polarized proton beams: jets, direct photon, lepton pairs (Drell-Yan), and WZ production is performed.
Abstract: We perform a systematic analysis of different processes with high energy polarized proton beams: jets, direct photon, lepton pairs (Drell-Yan) andWZ production. Different sets of polarized partonic densities are used that fit EMC and SLAC polarized deep inelastic scattering data with variable amount of quark and gluon components of the proton spin. The case of the future Relativistic Heavy Ion Collider (RHIC) used as a polarized collider at a maximum energy of\(\sqrt s = 500\) GeV is analyzed in detail.
TL;DR: In this paper, the dynamics of tris(trimethylammonium) nonachlorodiantimonate, which shows different phases as a function of temperature, were studied through proton spin lattice relaxation measurements at five Larmor frequencies.
21 Oct 1993
TL;DR: In this article, the value of power corrections to the integrals of the polarization structure functions of proton and neutron integral g{sub 1{sub p,n}(x)dx} measured by the EMC, SMC and E142 groups, is determined based on a model which accounts for higher twist terms, has the correct asymptotic behavior at large Q{sup 2, and satisfies the Gerasimov-Drell-Hearn sum rule at Q {sup 2}=0.
Abstract: The value of power corrections to the integrals of the polarization structure functions of proton and neutron integral g{sub 1{sub p,n}(x)dx} measured by the EMC, SMC and E142 groups, is determined based on a model which accounts for higher twist terms, has the correct asymptotic behavior at large Q{sup 2}, and satisfies the Gerasimov-Drell-Hearn sum rule at Q{sup 2}=0. The contribution of resonances up to W=1.8 GeV at Q{sup 2}=0 is taken into account based on the analysis of electroproduction data. It is shown that when taking into account these higher twist terms, the experimental data agree with the Bjorken sum rule, and the fraction of the proton spin projection carried by quarks, is consistent with the natural estimate of {approx} 50%.
TL;DR: In this article, a model for the spin lattice relaxation time of the protons of dimethylammonium in the Redfield limit and common spin temperature approximation was developed, considering the three fold reorientations of the methyl groups, the rotation of the whole molecular group around its two fold symmetric axis and possible correlations among these motions.
Abstract: A model for the spin lattice relaxation time of the protons of dimethylammonium in the Redfield limit and common spin temperature approximation is developed. The three fold reorientations of the methyl groups, the rotation of the whole molecular group around its two fold symmetric axis and possible correlations among these motions are considered. The effect of these processes on the dipolar interactions among the protons within the same molecular group is taken into account. The resulting relaxation rate is powder averaged and used to explain the experimental data in literature on [NH 2 (CH 3 ) 2 ] 3 Sb 2 Br 9 . The analysis shows that dynamically inequivalent groups exist in this compound and that the effect of proposed correlation among the different motions on the final results is negligible
TL;DR: In this article, a quasi-1-D diffusion model was proposed for the electronic spin motion in both materials with similar parameters, and the results were discussed with respect to other properties of the materials and to other materials, as well as to other conducting polymers.
TL;DR: In this paper, the dynamics of tris (tetra-methylammonium) nonabromodiantimonate, which shows structural phase transitions, were studied through proton spin lattice relaxation measurements (at two Larmor frequencies) and line width measurements.
01 Mar 1993
TL;DR: In this paper, the authors reported results of their calculation on the π N σ term and the flavor-singlet axial charge of the nucleon in the framework of quenched lattice QCD.
Abstract: We report results of our calculation on the π N σ term and the flavor-singlet axial charge of the nucleon in the framework of quenched lattice QCD. The disconnected insertions which involve contributions from the sea quarks are evaluated with the stochastic estimator with the Z 2 noise which yields minimum variances. We find the sea-quark contribution to the π N sigma term to be ∼ 1 2 − 1 4 of that of the dynamical fermion calculation. Whereas, the sea-quark contribution to the flavor-singlet g A is negative and large enough to cancel the valence (connected insertion) contribution substantially to resolve the “proton spin crisis”.
TL;DR: In this paper, the results of a detailed study of the large transverse momentum Drell-Yan process, pp --> (Gamma*, Z^*)X --> l^+l^- X at collider energies, with either one or both protons polarised, allowing the study of single and double spin asymmetries respectively.
Abstract: We present the results of a detailed study of the large transverse momentum Drell-Yan process, pp --> (Gamma^*, Z^*)X --> l^+l^- X at collider energies, with either one or both protons polarised, allowing the study of single- and double-spin asymmetries respectively. We show how these asymmetries obtained from angular distributions of the leptons in the Gamma^* (or Z^*) rest-frame, can be used to get information on the polarised parton distributions. Numerical results for the asymmetries and the cross-sections are presented, and the sensitivity of the asymmetries to the initial parton distributions indicates that these can be used as effective probes of the spin structure of the proton.
01 Sep 1993
TL;DR: In this article, the theory and phenomenology of deep inelastic polarized leptonnucleon scattering in the light of recent data with a deuteron target from the SMC at CERN and a Helium 3 target from SLAC were reviewed.
Abstract: We review the theory and phenomenology of deep inelastic polarized leptonnucleon scattering in the light of recent data with a deuteron target from the SMC at CERN and a Helium 3 target from the E142 experiment at SLAC. After including higher-order perturbative QCD corrections, mass corrections and updated estimates of higher-twist effects, we find good agreement with the basic Bjorken sum rule, and extract a consistent set of values for the quark contributions to the proton spin: ∆Σ ≡ ∆u + ∆d + ∆s = 0.27 ± 0.11 ∆u = 0.82 ± 0.04 , ∆d = −0.44 ± 0.04 , ∆s = −0.11 ± 0.04 which are consistent with chiral soliton models and indications from lattice estimates. We also mention the prospects for future experiments on the spin structure of the nucleon.
TL;DR: Based on statistical thermodynamic fluctuation arguments, it is shown for the first time that thermally excited spin-flip laser emission from the fusion product protons can occur in large tokamak devices that are entering the reactor regime of operation.
Abstract: Based on statistical theormodynamic fluctuation arguments, it is shown here for the first time that thermally excited spin-flip laser emission from the fusion product protons can occur in large tokamak devices that are entering the reactor regime of operation. Existing experimental data from TFTR support this conjecture, in the sense that these measurements are in complete agreement with the predictions of the quasilinear theory of the spin-flip laser.
01 Nov 1993-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, analytical expressions of transfer matrices representing successive transformations of the spinor wave function over one turn in circular accelerators are used to track the proton spin through isolated resonances.
Abstract: Analytical expressions of transfer matrices representing successive transformations of the spinor wave function over one turn in circular accelerators are used to track the proton spin through isolated resonances. The effects of synchrotron motion and of Siberian snakes are simulated. Results of these calculations agree very well with those which have been obtained previously from analytical approaches or from numerical simulation programs.
TL;DR: In this paper, the S A and S * C mesophases of the Ferroelectric Liquid Crystal Val.DOC were studied by means of longitudinal proton spin relaxation dispersion, and the frequency dependence of T 1 covering frequencies from 102 to 3 × 108 Hz at two different temperatures in each mesophase.
Abstract: Molecular dynamics studies were carried out in the S A and S * C mesophases of the Ferroelectric Liquid Crystal Val.DOC by means of longitudinal proton spin relaxation dispersion. Fast field-cycling and conventional Nuclear Magnetic Resonance (NMR) techniques were used to obtain the frequency dependence of T 1 covering frequencies from 102 to 3 × 108 Hz at two different temperatures in each mesophase. The T 1 dispersion in both mesophases could be well modeled by the proposed dominant relaxation mechanisms, namely collective motions, molecular self diffusion and local molecular rotations. A Soft mode contribution to the spin-lattice relaxation could not be singled out from the contribution of other collective motions. The diffusion constant D ⊥perpendicular to the director was obtained at all temperatures studied and involves an activation energy of about 35 kJ/mol. Effective correlation times characterizing the average molecular rotations around the long axis and fluctuations of this axis, respe...
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TL;DR: In this paper, the axial singlet current was shown to have a non-vanishing matrix element and a mechanism to disentangle the ''matter'' and ''glue'' contributions to this matrix element.
Abstract: It is demonstrated how in the soliton approach to baryons a small but non-vanishing matrix element of the axial singlet current is obtained. Furthermore it is shown that these models also provide a mechanism to disentangle the ``matter" and ``glue" contributions to this matrix element. Numerical results indeed exhibit a cancellation between these two components. However, the magnitudes of both turn out to be significantly smaller than unity.
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01 Jan 1993
TL;DR: In this paper, a theoretical viewpoint of the proton spin crisis is presented, and the results of the SMC experiment on polarized muon scattering off polarized nucleons are discussed.
Abstract: The SMC experiment on polarized muon scattering off polarized nucleons, G. Baum et al polarization at LEP - status and prospects, J.P. Koutchouk polarized protons at RHIC, Y. Makdisi recent developments in stored polarized electron positron beams, R. Rossmanith test of time-reversal invariance in proton-deuteron scattering, P.D. Eversheim spin correlation measurements at the Indiana University cyclotron facility, S.F. Pate the proton spin problem, theoretical viewpoint, A.V. Efremov QCD and EMC 2 - the proton spin crisis is still here, G. Preparata spin effects in elastic scattering and nonperturbative dynamics, S.M. Troshin high-spin structure of odd-A Os nuclei, D.L. Balabanski spin phenomena in elastic processes, M.P. Chavleishvili polarization effects in W-pair production in e+e- annihilation, J. Fleischer analysis of e+e- to pp process with polarized particles, J. Kraskiewicz and R. Raczka transverse spin effects, P.G. Ratcliffe. (Part contents).
TL;DR: In this paper, the overhauser shift ( ΔB ov ) of the electron spin resonance (ESR) line due to dynamic nuclear spin polarization (DNP) of the hyperfine coupled nuclei is observed for the fully doped, conducting form of polythiophene (PT) at 1.9 K. The average hyperfine coupling constant A zz is calculated to be ≈−5.6 MHz.
TL;DR: In this article, a second-order anomaly is introduced in a NOE-relayed heteronuclear correlation via single-quantum coherence spectra (SQC-NOESY) scheme.
TL;DR: In this article, the contribution of the mixing of the π0-meson and the ghost pole of the UA(1) problem to the pion-nucleon coupling constants is obtained.
TL;DR: In this article, the influence of glue-ball coupling to nucleons on the weak axial-vector coupling constants including the singlet channel was discussed and the possibility of the introduction of a constituent gluon contribution to the proton spin was considered.