Disconnected Electromagnetic Form Factors

Preliminary results of a calculation of disconnected nucleon electromagnetic factors factors on the lattice are presented. The implementation of the numerical subtraction scheme is outlined. A comparison of results for electric and magnetic disconnected form factors on two lattice sizes with those of the Kentucky group is presented. Unlike previous results, the results found in this calculation are consistent with zero in these sectors.Comment: Lattice 2000 (Hadronic Matrix Elements), 4 pages, 6 fig

Strange Magnetic Moment of The Nucleon from Lattice QCD

We calculate the strange magnetic moment of the nucleon on a quenched $16^3 \times 24$ lattice at $\beta = 6.0$, and with Wilson fermions at $\kappa$ = 0.148, 0.152, and 0.154. The strange quark contribution from the disconnected insertion is estimated stochastically by employing the $Z_2$ noise method. Using an unbiased subtraction along with the help of charge conjugation and hermiticity, we reduce the error by a factor of 2 with negligible overhead. Our result is $G_{M}^{s} = -0.28\pm0.10 \mu_{N}$.Comment: Lattice 2000 (Hadronic Matrix Elements), 4 pages 2 fig

Parity Violation with Electrons and Hadrons

A key question in understanding the structure of nucleons involves the role of sea quarks in their ground state electromagnetic properties such as charge and magnetism. Parity-violating electron scattering, when combined with determination of nucleon electromagnetic form factors from parity-conserving e-N scattering, provides another degree of freedom to separately determine the up, down and strange quark contributions to nucleon electromagnetic structure. Strange quarks are unique in that they are exclusively in the nucleon's sea. A program of experiments using parity violating electron scattering has been underway for approximately a decade, and results are beginning to emerge. This paper is a brief overview of the various experiments and their results to date along with a short-term outlook of what can be anticipated from experiments in the next few years.Comment: Invited talk at the 17th International IUPAP Conference on Few-Body Problems in Physic

An Energy Feedback System for the MIT/Bates Linear Accelerator

We report the development and implementation of an energy feedback system for the MIT/Bates Linear Accelerator Center. General requirements of the system are described, as are the specific requirements, features, and components of the system unique to its implementation at the Bates Laboratory. We demonstrate that with the system in operation, energy fluctuations correlated with the 60 Hz line voltage and with drifts of thermal origin are reduced by an order of magnitude

Heavy-quark contribution to the proton's magnetic moment

We study the contribution to the proton's magnetic moment from a heavy quark sea in quantum chromodynamics. The heavy quark is integrated out perturbatively to obtain an effective dimension-6 magnetic moment operator composed of three gluon fields. The leading contribution to the matrix element in the proton comes from a quadratically divergent term associated with a light-quark tensor operator. With an approximate knowledge of the proton's tensor charge, we conclude that a heavy sea-quark contribution to the proton's magnetic moment is positive in the asymptotic limit. We comment on the implication of this result for the physical strange quark.Comment: 4 pages, 2 figure

Strange form factors and Chiral Perturbation Theory

We review the contributions of Chiral Perturbation Theory to the theoretical understanding or not-quite-yet-understanding of the nucleon matrix elements of the strange vector current.Comment: 4 pages, 6 figures, presented at the International Workshop on Parity Violation and Hadronic Structure (PAVI04), Grenoble, France, 8-11 Jun 200

Relativistic Green's function approach to parity-violating quasielastic electron scattering

A relativistic Green's function approach to parity-violating quasielastic electron scattering is presented. The components of the hadron tensor are expressed in terms of the single particle Green's function, which is expanded in terms of the eigenfunctions of the non-Hermitian optical potential, in order to account for final state interactions without any loss of flux. Results for $^{12}$C, $^{16}$O, and $^{40}$Ca are presented and discussed. The effect of the strange quark contribution to the nuclear current is investigated.Comment: 24 pages, 13 figure

Proton strangeness form factors in (4,1) clustering configurations

We reexamine a recent result within a nonrelativistic constituent quark model (NRCQM) which maintains that the uuds\bar s component in the proton has its uuds subsystem in P state, with its \bar s in S state (configuration I). When the result are corrected, contrary to the previous result, we find that all the empirical signs of the form factors data can be described by the lowest-lying uuds\bar s configuration with \bar s in P state that has its uuds subsystem in $S$ state (configuration II). Further, it is also found that the removal of the center-of-mass (CM) motion of the clusters will enhance the contributions of the transition current considerably. We also show that a reasonable description of the existing form factors data can be obtained with a very small probability P_{s\bar s}=0.025% for the uuds\bar s component. We further see that the agreement of our prediction with the data for G_A^s at low-q^2 region can be markedly improved by a small admixture of configuration I. It is also found that by not removing CM motion, P_{s\bar s} would be overestimated by about a factor of four in the case when transition dominates over direct currents. Then, we also study the consequence of a recent estimate reached from analyzing the existing data on quark distributions that P_{s\bar s} lies between 2.4-2.9% which would lead to a large size for the five-quark (5q) system, as well as a small bump in both G^s_E+\eta G^s_M and G^s_E in the region of q^2 =< 0.1 GeV^2.Comment: Prepared for The Fifth Asia-Pacific Conference on Few-Body Problems in Physics 2011 in Seoul, South Korea, 22-26 August 201

Analyticity in a phenomenology of electro-weak structure of hadrons

The utility of an application of the analyticity in a phenomenology of electro-weak structure of hadrons is demonstrated in a number of obtained new and experimentally verifiable results. With this aim first the problem of an inconsistency of the asymptotic behavior of VMD model with the asymptotic behavior of form factors of baryons and nuclei is solved generally and a general approach for determination of the lowest normal and anomalous singularities of form factors from the corresponding Feynman diagrams is reviewed. Then many useful applications by making use of the analytic properties of electro-weak form factors and amplitudes of various electromagnetic processes of hadrons are carried out.Comment: 153 pages, Reviews&Tutorial

Mesonic Anapole Form Factors of the Nucleons

The chiral quark model posits pseudoscalar and vector meson couplings to constituent quarks. The parity violating meson-quark couplings lead to anapole moments and form factors of the nucleons. These arise both as parity violating meson loop fluctuations as well as exchange currents and polarization currents that are induced by the parity violating interaction between quarks. Because of cancellations between the different contributions the magnitude of the calculated anapole moments is only of the order $\sim 10^{-8}$ and is determined mainly by magnitude of the parity-violating meson-nucleon coupling constants.Comment: Figure 8 correcte