Showing papers on "Proton spin crisis published in 2002"
TL;DR: The anomalous magnetic moment of the negative muon has been measured to a precision of 0.7 ppm (ppm) at the Brookhaven Alternating Gradient Synchrotron, and is over an order of magnitude more precise than the previous measurement.
Abstract: We present the first results of the Fermilab National Accelerator Laboratory (FNAL) Muon g-2 Experiment for the positive muon magnetic anomaly a_{μ}≡(g_{μ}-2)/2. The anomaly is determined from the precision measurements of two angular frequencies. Intensity variation of high-energy positrons from muon decays directly encodes the difference frequency ω_{a} between the spin-precession and cyclotron frequencies for polarized muons in a magnetic storage ring. The storage ring magnetic field is measured using nuclear magnetic resonance probes calibrated in terms of the equivalent proton spin precession frequency ω[over ˜]_{p}^{'} in a spherical water sample at 34.7 °C. The ratio ω_{a}/ω[over ˜]_{p}^{'}, together with known fundamental constants, determines a_{μ}(FNAL)=116 592 040(54)×10^{-11} (0.46 ppm). The result is 3.3 standard deviations greater than the standard model prediction and is in excellent agreement with the previous Brookhaven National Laboratory (BNL) E821 measurement. After combination with previous measurements of both μ^{+} and μ^{-}, the new experimental average of a_{μ}(Exp)=116 592 061(41)×10^{-11} (0.35 ppm) increases the tension between experiment and theory to 4.2 standard deviations.
932 citations
TL;DR: In this article, it was shown that final-state interactions from gluon exchange between the outgoing quark and the target spectator system lead to single-spin asymmetries in deep inelastic lepton-proton scattering at leading twist in perturbative QCD; i.e., the rescattering corrections are not power-law suppressed at large photon virtuality Q2 at fixed xbj.
524 citations
TL;DR: In this article, it was shown that final-state interactions from gluon exchange between the outgoing quark and the target spectator system lead to single-spin asymmetries in deep inelastic lepton-proton scattering at leading twist in perturbative QCD; i.e., the rescattering corrections are not power-law suppressed at large photon virtuality Q^2 at fixed x_{bj}.
Abstract: Recent measurements from the HERMES and SMC collaborations show a remarkably large azimuthal single-spin asymmetries A_{UL} and A_{UT} of the proton in semi-inclusive pion leptoproduction. We show that final-state interactions from gluon exchange between the outgoing quark and the target spectator system lead to single-spin asymmetries in deep inelastic lepton-proton scattering at leading twist in perturbative QCD; i.e., the rescattering corrections are not power-law suppressed at large photon virtuality Q^2 at fixed x_{bj}. The existence of such single-spin asymmetries requires a phase difference between two amplitudes coupling the proton target with J^z_p = + 1/2 and -1/2 to the same final state, the same amplitudes which are necessary to produce a nonzero proton anomalous magnetic moment. We show that the exchange of gauge particles between the outgoing quark and the proton spectators produces a Coulomb-like complex phase which depends on the angular momentum L_z of the proton's constituents and is thus distinct for different proton spin amplitudes. The single-spin asymmetry which arises from such final-state interactions does not factorize into a product of distribution function and fragmentation function, and it is not related to the transversity distribution delta q(x,Q) which correlates transversely polarized quarks with the spin of the transversely polarized target nucleon.
414 citations
TL;DR: The model proposed accounts quantitatively for the proton spin‐lattice relaxation rates measured in immobilized protein systems at different water contents, and provides a fundamental basis for understanding the parametric dependence of proton spins in dynamically heterogeneous systems, such as tissues.
Abstract: The magnetic field dependence of the water-proton spin-lattice relaxation rate (1/T1) in tissues results from magnetic coupling to the protons of the rotationally immobilized components of the tissue. As a consequence, the magnetic field dependence of the water-proton (1/T1) is a scaled report of the field dependence of the (1/T1) rate of the solid components of the tissue. The proton spin-lattice relaxation rate may be represented generally as a power law: 1/T1ω = Aω−b, where b is usually found to be in the range of 0.5–0.8. We have shown that this power law may arise naturally from localized structural fluctuations along the backbone in biopolymers that modulate the proton dipole-dipole couplings. The protons in a protein form a spin communication network described by a fractal dimension that is less than the Euclidean dimension. The model proposed accounts quantitatively for the proton spin-lattice relaxation rates measured in immobilized protein systems at different water contents, and provides a fundamental basis for understanding the parametric dependence of proton spin-lattice relaxation rates in dynamically heterogeneous systems, such as tissues. Magn Reson Med 48:21–26, 2002. © 2002 Wiley-Liss, Inc.
77 citations
TL;DR: In this article, the Brueckner-Hartree-Fock formalism was used to study the properties of spin-polarized isospin asymmetric nuclear matter.
Abstract: Properties of spin-polarized isospin asymmetric nuclear matter are studied within the framework of the Brueckner-Hartree-Fock formalism. The single-particle potentials of neutrons and protons with spin up and down are determined for several values of the neutron and proton spin polarizations and the asymmetry parameter. It is found that the single-particle potentials exhibit an almost linear and symmetric variation as a function of these parameters. An analytic parametrization of the total energy per particle as a function of the asymmetry and spin polarizations is constructed. This parametrization is employed to compute the magnetic susceptibility of nuclear matter for several values of the asymmetry from neutron to symmetric matter. The results show no indication of a ferromagnetic transition at any density for any asymmetry of nuclear matter.
76 citations
TL;DR: The shielding anisotropy sigma(parallel)-sigma(perpendicular) is obtained by measuring the proton spin relaxation rate as a function of magnetic induction field in a water sample where dipole-dipole couplings are suppressed by H/D isotope dilution.
Abstract: The nuclear magnetic shielding tensor is a sensitive probe of the local electronic environment, providing information about molecular structure and intermolecular interactions. The magnetic shielding tensor of the water proton has been determined in hexagonal ice, but in liquid water, where the tensor is isotropically averaged by rapid molecular tumbling, only the trace of the tensor has been measured. We report here the first determination of the proton shielding anisotropy in liquid water, which, when combined with chemical shift data, yields the principal shielding components parallel (sigma(parallel)) and perpendicular (sigma(perpendicular)) to the O-H bond. We obtained the shielding anisotropy sigma(parallel)-sigma(perpendicular) by measuring the proton spin relaxation rate as a function of magnetic induction field in a water sample where dipole-dipole couplings are suppressed by H/D isotope dilution. The temperature dependence of the shielding components, determined from 0 to 80 degrees C, reflects vibrational averaging over a distribution of instantaneous hydrogen-bond geometries in the liquid and thus contains unique information about the temperature-dependent structure of liquid water. The temperature dependence of the shielding anisotropy is found to be 4 times stronger than that of the isotropic shielding. We analyze the liquid water shielding components in the light of previous NMR and theoretical results for vapor and ice. We show that a simple two-state model of water structure fails to give a consistent interpretation of the shielding data and we argue that a more detailed analysis is needed that quantitatively relates the shielding components to hydrogen bond geometry.
56 citations
TL;DR: The leading chiral contributions to the quark and gluon components of the proton spin are calculated using heavy-baryon chiral perturbation theory and can serve as a guide for extrapolating lattice QCD calculations at large quark masses to the chiral limit.
Abstract: The leading chiral contributions to the quark and gluon components of the proton spin are calculated using heavy-baryon chiral perturbation theory. Similar calculations are done for the moments of the generalized parton distributions relevant to the quark and gluon angular momentum densities. These results provide useful insight into the role of pions in the spin structure of the nucleon and can serve as a guide for extrapolating lattice QCD calculations at large quark masses to the chiral limit.
53 citations
TL;DR: In this article, it was shown that the probability of β electrons being in excess over α electrons at the position of nucleus n, given that there is an α electron at n, is proportional to the negative of the exchange density, the total Fermi correlation between n and n.
Abstract: The spin−spin coupling of protons measured by the constant JHH‘ in NMR experiments is dominated by a term proportional to the product of the electron spin densities at the two nuclei, the Fermi contact term. The probability of β electrons being in excess over α electrons at the position of nucleus n‘, given that there is an α electron at n, is proportional to the negative of the exchange density, the total Fermi correlation between n and n‘. Thus the delocalization of the Fermi hole between n and n‘ is the mechanism whereby the spin perturbation caused by the magnetic interaction of an electron with nucleus n is transmitted to n‘. The density and exchange density within the basin of a hydrogen atom are described primarily in terms of s-type basis functions, and one may approximate the exchange density between two protons at n and n‘ by the exchange between the two associated atomic basins determined by the delocalization index δ(A,B) within the quantum theory of atoms in molecules. It is shown that this m...
51 citations
TL;DR: In this article, the spin-lattice relaxation rate T - 1 1 and NMR spectra of 1 H in single crystal of molecular magnets Fe8 have been measured down to 15 mK.
Abstract: The spin-lattice relaxation rate T - 1 1 and NMR spectra of 1 H in single crystal of molecular magnets Fe8 have been measured down to 15 mK. The relaxation rate T - 1 1 shows a strong temperature dependence down to 400 mK. The relaxation is well explained in terms of the thermal transition of the iron state between the discreet energy levels of the total spin S = 10. The relaxation time T 1 becomes temperature independent below 300 mK and is longer than 100 s. In this temperature region stepwise recovery of the 1 H-NMR signal after saturation was observed depending on the return field of the sweep field. This phenomenon is attributed to the resonant quantum tunneling at the fields where levels cross and is discussed in terms of the Landau-Zener transition.
20 citations
TL;DR: In this article, a colored-quark-cluster model was proposed, which is compatible with a quark-diquark picture while the richness of the experimentally known states require three particles to participate in the dynamics.
Abstract: Light-baryon resonances (with u,d, and s quarks in the SU(3) classification) fall on Regge trajectories. When their squared masses are plotted against the intrinsic orbital angular momenta {\rm L}, $\Delta^*$'s with even and odd parity can be described by the same Regge trajectory. For a given {\rm L}, nucleon resonances with spin {\rm S}=3/2 are approximately degenerate in mass with $\Delta$ resonances. To which total angular momentum {\rm L} and {\rm S} couple has no significant impact on the baryon mass. Nucleons with spin 1/2 are shifted in mass; the shift is - in units of squared masses - proportional to the component in the wave function which is antisymmetric in spin and flavor. Based on these observations, a new baryon mass formula is proposed which reproduces nearly all known baryon masses. It is shown that the masses are compatible with a quark-diquark picture while the richness of the experimentally known states require three particles to participate in the dynamics. This conflict is resolved by proposing that quarks polarize the QCD condensates and are surrounded by a polarization cloud shielding the color. A new interpretation of constituent quarks as colored quark clusters emerges; their interaction is responsible for the mass spectrum. Fast flavor exchange between the colored quark clusters exhausts the dynamical richness of the three-particle dynamics. The colored-quark-cluster model provides a mechanism in which the linear confinement potential can be traced to the increase of the volume in which the condensates are polarized. The quark-spin magnetic moment induces currents in the polarized condensates which absorb the quark-spin angular momentum: the proton spin is not carried by quark spins. The model provides a new picture of hybrids and glueballs.
17 citations
CERN1
TL;DR: The present status of the proton spin problem and the physics possibilities for future polarized ep and pp colliders are summarized in this article, 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).
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).
Dissertation•
01 Jan 2002
TL;DR: In this paper, the authors propose a method to solve the problem of the problem: this paper... ]..,.. )].. [1].
Abstract: ii
TL;DR: Proton spin lattice relaxation time was measured and proton NMR spectrum was observed in a purely molecular ferroelectrics, trichloroacetamide (TCAA) as mentioned in this paper.
Abstract: Proton spin lattice relaxation time was measured and proton NMR spectrum was observed in a purely molecular ferroelectrics, trichloroacetamide (TCAA). From the temperature and the frequency depende...
TL;DR: In this paper, the authors analyzed under which conditions the interaction derived from the gluonic pole exchange might explain the high momentum transfer behavior of the photoproduction cross sections of vector mesons at JLab energies.
01 Feb 2002
TL;DR: In this paper, the relation between the spin structure of the proton and the axial U(1) problem is discussed and new experiments motivated by the Proton spin problem which could shed light on the nature of symmetry breaking in QCD are discussed.
Abstract: We emphasise the relation between the spin structure of the proton and the axial U(1) problem. New experiments motivated by the proton spin problem which could shed light on the nature of U(1) symmetry breaking in QCD are discussed.
Posted Content•
TL;DR: In this article, the color boundary term was exploited to obtain the missing piece in the axial charge associated with the gluon Casimir effect. And the result is that the flavor singlet axial current is small independent of the confinement (bag) size.
Abstract: The flavor singlet axial charge has been a source of study in the last years due to its relation to the so called {\it Proton Spin Problem}. The relevant flavor singlet axial current is anomalous, i.e., its divergence contains a piece which is the celebrated $U_A(1)$ anomaly. This anomaly is intimately associated with the $\eta^\prime$ meson, which gets its mass from it. When the gauge degrees of freedom of QCD are confined within a volume as is presently understood, the $U_A(1)$ anomaly is known to induce color anomaly leading to "leakage" of the color out of the confined volume (or bag). For consistency of the theory, this anomaly should be cancelled by a boundary term. This ``color boundary term" inherits part or most of the dynamics of the volume (i.e., QCD). In this thesis, we exploit this mapping of the volume to the surface via the color boundary condition to perform a complete analysis of the flavor singlet axial charge in the chiral bag model using the Cheshire Cat Principle. This enables us to obtain the hitherto missing piece in the axial charge associated with the gluon Casimir effect. The result is that the flavor singlet axial charge is small independent of the confinement (bag) size ranging from the skyrmion picture to the MIT bag picture, thereby confirming the (albeit approximate) Cheshire Cat phenomenon.
01 Jan 2002
TL;DR: The n-p spin correlation parameter Azx was measured at an energy of 66:24 MeV and 5 angles in the range of 25oi46o CM with a statistical precision better than 0:01 as mentioned in this paper.
Abstract: The n-p spin correlation parameter Azx was measured at an energy
of 66:24 MeV and 5 angles in the range of 25oi46o CM with a statistical
accuracy better than 0:01
In the measured range, Azx is most sensitive to ²1, the mixing parameter
of the deuteron states 2S1 and 2D1 Therefore the measurement
is expected to reduce significantly the uncertainties of the phases in the
energy range below 100 MeV, when a new global Phase Shift Analysis
(PSA) is performed This should help to find a more accurate answer to
the strength of the tensor force in the NN-interaction
The experiment was performed in the low energy area C (NEC) of
the Paul Scherrer Institute (PSI) in Villigen, Switzerland
TL;DR: In this paper, an account of the X-ray structure, the solid-state carbon spectra and carbon and proton relaxation times of solid crystalline L-leucinamide is given.
TL;DR: In this article, the STAR collaboration aims to determine directly and precisely the gluon polarization, as well as the polarizations of the u, u, d and d quarks in the proton by measuring in addition longitudinal and double spin asymmetries.
Abstract: The STAR collaboration aims to study polarized proton-proton collisions at RHIC. The emphasis of the spin run this year is on transverse single spin asymmetries. Beyond 2001, we aim to determine directly and precisely the gluon polarization, as well as the polarizations of the u, $\bar{u}$, d and $\bar{d}$ quarks in the proton by measuring in addition longitudinal and double spin asymmetries. Furthermore, we aim to measure for the first time the quark transversity distributions. These measurements will improve substantially the knowledge and understanding of the spin structure of the nucleon.
01 Feb 2002
TL;DR: In this article, the authors review recent progress concerning the various nuclear corrections that must be applied to measurements on polarised 3 He and show that 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.
Abstract: The neutron spin structure function, g 1 n , 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.
04 Nov 2002
TL;DR: In this article, the single particle potentials of neutrons and protons with spin up and down are determined for several values of the neutron and proton spin polarizations and the asymmetry parameter, and an analytic parametrization of the total energy per particle as a function of these parameters is constructed.
Abstract: Bulk and single‐particle properties of spin polarized isospin asymmetric nuclear matter are studied within the framework of the Brueckner‐Hartree‐Fock approximation The single‐particle potentials of neutrons and protons with spin up and down are determined for several values of the neutron and proton spin polarizations and the asymmetry parameter An analytic parametrization of the total energy per particle as a function of these parameters is constructed, and employed to compute the magnetic susceptibility of nuclear matter The results show no indication of a ferromagnetic transition at any density for any asymmetry of nuclear matter
01 Feb 2002
TL;DR: In this paper, the capabilities of a neutrino factory in the determination of polarized parton distributions from charged-current deepinelastic scattering experiments is discussed, and the accuracy of the determination is analyzed.
Abstract: The capabilities of a neutrino factory in the determination of polarized parton distributions from charged—current deep—inelastic scattering experiments is discussed. We present a study of the accuracy in the determination of polarized parton distributions that would be possible with such a facility. We show that these measurements have the potential to distinguish between different theoretical scenarios for the proton spin structure.
24 Jun 2002
TL;DR: In this article, an overview of the evolution of proton-proton spin physics over the past quarter century is presented, and recent work on interpreting high energy polarization effects in a constituent scattering model is described.
Abstract: In this paper the author presents an overview of the evolution of proton‐proton spin physics over the past quarter century and describes recent work on interpreting high energy polarization effects in a constituent scattering model.
TL;DR: In this article, the authors investigated the spin structure of the nucleon in an extended Jaffe-Lipkin quark model, and showed that the Jaffe Lipschitz term is only important when antiquarks are negatively polarized.
Abstract: We investigate the spin structure of the nucleon in an extended Jaffe-Lipkin quark model. In addition to the conventional $3q$ structure, different $(3q)(Q\bar{Q})$ admixtures in the nucleon wavefunction are also taken into account. The contributions to the nucleon spin from various components of the nucleon wavefunction 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".