Precise determination of the strangeness magnetic moment of the nucleon

By combining the constraints of charge symmetry with new chiral extrapolation techniques and recent low mass quenched lattice-QCD simulations of the individual quark contributions to the magnetic moments of the nucleon octet, we obtain a precise determination of the strange magnetic moment of the proton. The result, namely, G(s)(M)=(-0.046 +/- 0.019)mu(N) is consistent with the latest experimental measurements but an order of magnitude more precise. This poses a tremendous challenge for future experiments.     

ss component of the proton and the strangeness magnetic moment

A complete analysis is given of the implications of the empirical indications for a positive strangeness magnetic moment mu(s) of the proton on the possible configurations of the uudss component of the proton. A positive value for mu(s) is obtained in the ss configuration where the uuds subsystem is in an orbitally excited state with [4](FS)[22](F)[22](S) flavor-spin symmetry, which is likely to have the lowest energy. The configurations in which the s is orbitally excited, which include the conventional Kappa(+)lambda(0) configuration, with the exception of that in which the uuds component has spin 2, yield negative values for mu(s). The hidden strangeness analogues of recently proposed quark cluster models for the theta(+) pentaquark give differing signs for mu(s).     

Global analysis of the strangeness vector and axial form factors of the nucleon and their uncertainties

We have studied the strangeness contribution to the elastic vector and axial form factors of the nucleon, using all available electroweak elastic scattering data sensitive to these contributions. Specifically, we combine ??p and $\bar{\nu} p$ elastic scattering cross sections from Brookhaven E734 with parity-violating asymmetries in elastic ep scattering, and quasi-elastic ed and e ⁴He scattering, observed in the SAMPLE, HAPPEx, G0 and PVA4 experiments. We are able not only to determine these form factors at individual values of momentum-transfer (Q ²), as has been done recently, but also to fit the Q ²-dependence of these form factors using simple functional forms. We present the results of these fits using existing data.     

Flavor symmetry breaking and strangeness in the nucleon

We suggest that breaking of SU(3) flavor symmetry mainly resides in the baryon wave functions while the charge operators have no (or only small) explicit symmetry-breaking components. We utilize the collective coordinate approach to chiral soliton models to support this picture. In particular we compute the g _A /g _V ratios for hyperon beta-decay and the strangeness contribution to the nucleon axial current matrix elements and analyze their variation with increasing flavor symmetry breaking.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.39.Dc Skyrmions - 12.39.Fe Chiral Lagrangians - 13.30.Ce Leptonic, semileptonic, and radiative decays - 14.20.Jn HyperonsH. Weigel: Heisenberg-Fellow;     

On the instanton-induced portion of the nucleon strangeness

We calculate the instanton contribution to the proton strangeness in an MIT bag enriched by the presence of a dilute instanton liquid. The evaluation is based on the expression of the nucleon matrix elements of bilinear strange-quark operators in terms of a model valence nucleon state and the interactions producing quark–antiquark fluctuations on top of that valence state. Our method combines use of the the evolution operator containing a strangeness source and the Feynman–Hellmann theorem. It enables one to evaluate the strangeness in different Lorentz channels in essentially the same way. Only the scalar channel is found to be affected by the interaction induced by the random instanton liquid. Received: 12 February 1999 / Published online: 30 June 1999     

Gluon exchange corections to the nucleon magnetic moment in the mit bag model

We have calculated gluon exchange corrections to the nucleon magnetic moment predictions of the MIT bag model. The sizeable coupling constant $\text{g}{}^2{}_{\mathrm{c}}\text{/}\text{4π=0.5}$ does not produce an enormous correction (≈10%), but it is in the wrong direction to ameliorate the present 30% disagreement with experiment.     

Neutrino dimuon production and the strangeness asymmetry of the nucleon

We have performed the first global QCD analysis to include the CCFR and NuTeV dimuon data, which provide direct constraints on the strange and antistrange parton distributions, s(x) and . To explore the strangeness sector, we adopt a general parametrization of the non-perturbative functions satisfying basic QCD requirements. We find that the strangeness asymmetry, as represented by the momentum integral , is sensitive to the dimuon data provided the theoretical QCD constraints are enforced. We use the Lagrange multiplier method to probe the quality of the global fit as a function of [S ^-] and find -0.001 < [S ^-] < 0.004. Representative parton distribution sets spanning this range are given. Comparisons with previous work are made.Received: 15 January 2004, Revised: 23 November 2004, Published online: 15 February 2005PACS: 11.30.Hv, 12.15.-y, 13.15. + g, 12.38.-t, 13.60.Hb     

Accurate determination of Be magnetic moment

The determination of the magnetic moment of ⁹Be from the measured ratio of the nuclear to the electron g-factors g_I/g_J in ⁹Be⁺ is presented. The obtained result μ(⁹Be)=-1.17743159(3)μ_N is two orders of magnitude more accurate than the presently accepted value.     

Non-standard physics and nucleon strangeness in low-energy PV electron scattering

Contributions from physics beyond the Standard Model, strange quarks in the nucleon, and nuclear structure effects to the left-right asymmetry measured in parity-violating (PV) electron scattering from¹²C and the proton are discussed. It is shown how lack of knowledge of the distribution of strange quarks in the nucleon, as well as theoretical uncertainties associated with higher-order dispersion amplitudes and nuclear isospin-mixing, enter the extraction of new limits on the electroweak parametersS andT from these PV observables. It is found that a series of elastic PV electron scattering measurements using⁴He could significantly constrain thes-quark electric form factor if other theoretical issues are resolved. Such constraints would reduce the associated form factor uncertainty in the carbon and proton asymmetries below a level needed to permit extraction of interesting low-energy constraints onS andT from these observables. For comparison, the much smaller scale ofs-quark contributions to the weak charge measured in atomic PV is quantified. It is likely that only in the case of heavy muonic atoms could nucleon strangeness enter the weak charge at an observable level.     

Extraction of hyperfine anomalies without precise values of the nuclear magnetic dipole moment

A new method for extracting the hyperfine anomaly from experimental hyperfine structure constants is suggested. Instead of independent high-precision measurements of the nuclear magnetic dipole moment, precise measurements of magnetic dipole hyperfine interaction constants for two atomic states and a theoretical analysis can be used. This can lead to determination of hyperfine anomaly for radioactive isotopes where the nuclear magnetic dipole moment is not known with high accuracy. Received: 17 February 1998     

Strange quarks in the nucleon and neutron electric dipole moment

Arguments in favour of a large value of the matrix element \(\left\langle {N\left| {\bar ss} \right|N} \right\rangle \) based on semiphenomenological data and low-energy theorems are given. As an application of these considerations, we study the contribution of strange quarks to the neutron electric dipole moment.     

On the instanton-induced portion of the nucleon strangeness II: the MIT model beyond the linearized approximation

If instantons are introduced into the MIT bag model in such a way that the bag radii are allowed to vary, the MIT bag interior can accommodate an instanton density which is by an order of magnitude larger than in the case when the radii are fixed (although it is still significantly smaller than in the non-perturbative QCD vacuum). The instanton contribution to the baryon mass shifts is also correspondingly larger. The instanton-induced part of the scalar strangeness of the nucleon MIT bag is an order of magnitude larger than found previously, within the linearized approximation. The decrease of the model radii (which is associated with the increase of the instanton density) is very favorable from the standpoint of nuclear physics. Received: 7 February 2003 / Revised version: 1 April 2003 / Published online: 23 May 2003 RID="a" ID="a" e-mail: klabucar@phy.hr RID="b" ID="b" e-mail: kkumer@phy.hr RID="c" ID="c" e-mail: dmekter@rudjer.irb.hr RID="d" ID="d" e-mail: bp@phy.hr. Present address: Faculty of Civil Engineering, University of Rijeka, HR-51000 Rijeka, Croatia     

Anapole moment and other constraints on the strangeness conserving Hadronic weak interaction

Standard analyses of low-energy NN and nuclear parity-violating observables have been based on a pi-, rho-, and omega-exchange model capable of describing all five independent s-p partial waves. Here a parallel analysis is performed for the one-body, exchange-current, and nuclear polarization contributions to the anapole moments of 133Cs and 205Tl. The resulting constraints are not consistent, though there remains some degree of uncertainty in the nuclear structure analysis of the atomic moments.     

Phenomenological determination of polarized quark distributions in the nucleon

We present a fit to spin asymmetries which gives polarized quark distributions. These functions are closely related to the ones given by the Martin, Roberts and Stirling fit for unpolarized structure functions. The integrals of polarized distributions are discussed and compared with the corresponding quantities obtained from neutron and hyperonβ-decay data. We use the combination of proton, neutron and deuteron spin asymmetries in order to determine the coefficients of our polarized quark distributions. Our fit shows that phenomenologically there is no need for taking polarized gluons into account.     

Phenomenological determination of polarized quark distributions in the nucleon

We present a fit to spin asymmetries which gives polarized quark distributions. These functions are closely related to the ones given by the Martin, Roberts and Stirling fit for unpolarized structure functions. The integrals of polarized distributions are discussed and compared with the corresponding quantities obtained from neutron and hyperonβ-decay data. We use the combination of proton, neutron and deuteron spin asymmetries in order to determine the coefficients of our polarized quark distributions. Our fit shows that phenomenologically there is no need for taking polarized gluons into account. Work supported in part by the KBN-Grant 2-P302-143-06     

Phenomenological determination of polarized quark distributions in the nucleon

We present a fit to spin asymmetries which gives polarized quark distributions. These functions are closely related to the ones given by the Martin, Roberts and Stirling fit for unpolarized structure functions. The integrals of polarized distributions are discussed and compared with the corresponding quantities obtained from neutron and hyperon??-decay data. We use the combination of proton, neutron and deuteron spin asymmetries in order to determine the coefficients of our polarized quark distributions. Our fit shows that phenomenologically there is no need for taking polarized gluons into account.