Showing papers on "Proton spin crisis published in 2001"

The physical basis for the magnetic field dependence of proton spin-lattice relaxation rates in proteins

Abstract: The magnetic field dependence of the proton spin-lattice relaxation rate in polymeric materials and biological macromolecules may report important dynamical information. In the case where the system is dynamically heterogeneous as in plasticized polymeric systems or hydrated biopolymers, the spin-lattice relaxation of the liquid-proton population is generally coupled to the spin-relaxation behavior of the solid spins that often dominate the observable response of the liquid. In many of these systems the magnetic field dependence of the proton spin-lattice relaxation rate may be represented as a power law: 1/T1(ω)=Aω−b where a is a constant and b is usually found to be in the range of 0.5 to 0.8. We have shown that this power law may arise naturally from localized structural fluctuations along the backbone of chain molecules that modulate the proton dipole–dipole couplings, which form a network described by a fractal dimension that may be less than the Euclidean dimension. When the model for the solid spin...

Polarized parton distributions from charged-current deep-inelastic scattering and future neutrino factories

Abstract: We discuss the determination of polarized parton distributions from charged-current deep-inelastic scattering experiments. We summarize the next-to-leading order treatment of charged-current polarized structure functions, their relation to polarized parton distributions and scale dependence, and discuss their description by means of a next-to-leading order evolution code. We discuss current theoretical expectations and positivity constraints on the unmeasured C-odd combinations Delta q-Delta qbar of polarized quark distributions, and their determination in charged-current deep-inelastic scattering experiments. We give estimates of the expected errors on charged-current structure functions at a future neutrino factory, and perform a study of the accuracy in the determination of polarized parton distributions that would be possible at such a facility. We show that these measurements have the potential to distinguish between different theoretical scenarios for the proton spin structure.

Understanding the proton spin “puzzle” with a new “minimal” quark model

Abstract: We investigate the spin structure of the nucleon in an extended Jaffe-Lipkin quark model. In addition to the conventional 3q structure, different (3q)(Q ) admixtures in the nucleon wave function are also taken into account. The contributions to the nucleon spin from various components of the nucleon wave function are discussed. The effect due to the Melosh-Wigner rotation is also studied. It is shown that the Jaffe-Lipkin term is only important when antiquarks are negatively polarized. We arrive at a new “minimal” quark model, which is close to the naive quark model, in order to understand the proton spin “puzzle”.

Anomalous Larmour Frequency Dependence of Proton Spin–Lattice Relaxation Time (T1) in the Ferroelectric Glycine Phosphite

Abstract: We report here the results of our $^{1}H$ NMR spin lattice relaxation time $(T_1)$ studies in glycine phosphite which is ferroelectric below 224 K. The experiments have been carried out in the temperature range from 200 to 419 K and at two Larmour frequencies of 11.40 and 23.56 MHz. We have noticed a Larmour frequency dependence of $T_1$ on the high-temperature side of the $T_1$ minimum. A model is proposed based on the BPP theory to explain the observation.

Muon physics possibilities at a muon-neutrino factory

Abstract: New intense proton accelerators with above GeV energies and MW beam power, such as they are discussed in connection with neutrino factories, appear to be excellently suited for feeding bright muon sources for low-energy muon science. Muon rates with several orders of magnitude increased flux compared to present facilities will become available. This will allow higher precision in experiments which were statistics limited so far such as searches for rare decays, muonium spectroscopy, muon capture, muon catalyzed fusion, muon decay studies and measurements muon moments and parameters. Novel and most important experiments will become possible. For example a permanent electric dipole moment (edmμ) of a muon could be searched with by far unprecedented accuracy and with a physics potential well beyond the possibilities of present electron, neutron and nuclear edm searches. Investigations of short lived radioactive nuclei using muonic atom spectroscopy would become feasible.

The Spin Structure of the Proton and Polarized Collider Physics

Abstract: We summarise the present status of the proton spin problem and the physics possibilities for future polarized ep and pp colliders. This summary is based on the presentations and discussion sessions at the workshop ``The Spin Structure of the Proton and Polarized Collider Physics'' (Trento, July 23-28, 2001).

Muon conversion experiments—current and future

Abstract: Many extensions of the standard model predict muon to electron conversion in the process μ+Nucleus→e+Nucleus at ratios, R, of 10−14 to 10−17 muon captures. A long history of experiments which have improved upper limits on R, to the current value of <6.1×10−13 set by SINDRUM II, have been limited by muon statistics rather than background. A new experiment, MECO, has been proposed to search for muon to electron conversion at levels below 5×10−17. MECO takes advantage of a pulsed, high-flux muon beam produced when a proton beam at the Brookhaven AGS is incident on a target in a graded solenoidal field. The detector has 800 KeV momentum resolution and is designed to minimize the background from the beam and maximize efficiency for signal electrons. With 1011 stopped muons per second, R=10−16 would give 5 detected events in a year of running with less than 0.5 background events expected.

The spin structure of the nucleon

Abstract: The measurements of the spin structure functions for the proton and neutron are reviewed. Recent high–precision data have allowed the Bjorken sum rule to be verified to within ca . 10% accuracy, providing a rigorous test of quantum chromodynamics, the current theory of strong interactions. The data show that there is a deficit between the spin carried by the quarks and the spin of the nucleon, as measured in deep–inelastic scattering. The theories of the deficit are discussed.

Spin physics program at STAR

Abstract: The question as to how spin degrees of freedom in nucleons are organized (“spin puzzle”) is ongoing. Quantifying the gluon polarization, not measured directly in DIS experiments, has been emphasized as necessary to complete the picture. The role of STAR in providing a definitive measurement of the gluon spin structure function is discussed, and other spin topics of current interest at RHIC energies summarized.

Measurement of spin observables in exclusive p̄p→Λ̄Λ production

Abstract: The PS185 experiment at LEAR has produced a wealth of high precision measurements of cross-sections and final state polarization observables in near-threshold antihyperon-hyperon production from antiproton-proton annihilation. In its most recent run, PS185/3 extended its capabilities by utilizing a transversely polarized frozen spin target to measure exclusive ΛΛ production. This allows access to a broad set of spin observables involving initial state spin. Competing theoretical models for this reaction have differing predictions for some of these newly-accessible spin observables, most notably the depolarization Dnn. This data is expected to provide a rigorous test of these models. Current results from the analysis of this data are presented.

The spin structure function of the neutron

Abstract: The neutron spin structure function, $g_{1n}$, has been of considerable interest recently in connection with the Bjorken sum rule and the proton spin crisis. Work on this problem has concentrated on measurements at low-$x$. We recall the important, non-perturbative physics to be learnt by going instead to larger values of $x$ and especially from a determination of the place where the expected sign change occurs. Of course, in order to obtain neutron data one must use nuclear targets and apply appropriate corrections. In this regard, we review recent progress concerning the various nuclear corrections that must be applied to measurements on polarised $^3$He.

Nuclear Spin Echo in Magnetic Fluids

Abstract: The two-pulse proton spin echo signal decay was studied in benzene-based magnetic fluids containing magnetite (filler) and oleic acid (surfactant). The spin echo signal decay rate increases with the magnetic filler concentration. A decrease in the transverse proton relaxation time is due to the increasing inhomogeneity of the local nuclear magnetic fields.

[Concerning measurements of the self-diffusion coefficient of water molecules and time of proton spin-lattice relaxation in plant tissues].

Abstract: Measurements of the coefficient of water molecules self-diffusion (D) and the time of spin-lattice relaxation (T1) in prosenchyme (elongated) plant cells, whose length significantly exceeding their transverse size, show that the orientation of plant tissues in the H0 field significantly affects the measured parameters. We conclude that this effect should be taken into account in experiments on the measurement of self-diffusion coefficients and time of proton spin-lattice relaxation in plant tissues containing prosenchyme cells.

Proton spin from general colour symmetry model

Abstract: The quark wavefunction in a proton has been calculated by using the global colour symmetry model. We find that the property of this wavefunction is closely related to the nonperturbative vacuum configuration. Using the wavefunction we make the calculation of the matrix element of the axial vector current of the quarks in the proton ground state. Its value is found to be 0.17, which is perfectly consistent with 0.23(+6).