126 research outputs found
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
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
Strange Magnetic Moment of The Nucleon from Lattice QCD
We calculate the strange magnetic moment of the nucleon on a quenched lattice at , and with Wilson fermions at =
0.148, 0.152, and 0.154. The strange quark contribution from the disconnected
insertion is estimated stochastically by employing the 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 .Comment: Lattice 2000 (Hadronic Matrix Elements), 4 pages 2 fig
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
The strangeness form factors of the proton
The present empirical information on the strangeness form factors indicates
that the corresponding component in the proton is such that the
subsystem has the flavor spin symmetry and mixed
orbital symmetry . This configuration leads to the
empirical signs of all the form factors , and . An
analysis with simple quark model wave functions for the preferred configuration
shows that the qualitative features of the empirical strangeness form factors
may be described with a 15% admixture of with a compact
wave function in the proton. Transition matrix elements between the and
the components give significant contributions
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
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
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 and is
determined mainly by magnitude of the parity-violating meson-nucleon coupling
constants.Comment: Figure 8 correcte
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
C, O, and Ca are presented and discussed. The effect of
the strange quark contribution to the nuclear current is investigated.Comment: 24 pages, 13 figure
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