44 research outputs found
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
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
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
Don't Forget to Measure
This talk explores our lack of knowledge of the strange quark contribution to
the nucleon spin, . Data on from inclusive and
semi-inclusive polarized deep-inelastic scattering will be reviewed, followed
by a discussion of how the ongoing program of parity-violating elastic
electron-nucleon scattering experiments, that seek out the strange
electromagnetic form factors of the nucleon, need to have an estimate for the
strange axial form factor to carry out that program, and how the value of
extracted from the DIS experiments has filled that role. It is shown
that elastic , , and parity-violating data can
be combined to extract the strange electric, magnetic axial form factors
simultaneously. A proposed experiment that could address this important issue
if briefly previewed.Comment: 4 pages, to appear in proceedings in PAVI04, Eur. Jour. Phy
Hadronic Parity Violation and Inelastic Electron-Deuteron Scattering
We compute contributions to the parity-violating (PV) inelastic
electron-deuteron scattering asymmetry arising from hadronic PV. While hadronic
PV effects can be relatively important in PV threshold electro- disintegration,
we find that they are highly suppressed at quasielastic kinematics. The
interpretation of the PV quasielastic asymmetry is, thus, largely unaffected by
hadronic PV.Comment: 27 pages, 13 figures, uses REVTeX and BibTe
The Strange Quark Contribution to the Proton's Magnetic Moment
We report a new determination of the strange quark contribution to the
proton's magnetic form factor at a four-momentum transfer Q2 = 0.1 (GeV/c)^2
from parity-violating e-p elastic scattering. The result uses a revised
analysis of data from the SAMPLE experiment which was carried out at the
MIT-Bates Laboratory. The data are combined with a calculation of the proton's
axial form factor GAe to determine the strange form factor GMs(Q2=0.1)=0.37 +-
0.20 +- 0.26 +- 0.07. The extrapolation of GMs to its Q2=0 limit and comparison
with calculations is also discussed.Comment: 6 pages, 1 figure, submitted to Phys. Lett.
The SAMPLE Experiment and Weak Nucleon Structure
One of the key elements to understanding the structure of the nucleon is the
role of its quark-antiquark sea in its ground state properties such as charge,
mass, magnetism and spin. In the last decade, parity-violating electron
scattering has emerged as an important tool in this area, because of its
ability to isolate the contribution of strange quark-antiquark pairs to the
nucleon's charge and magnetism. The SAMPLE experiment at the MIT-Bates
Laboratory, which has been focused on s-sbar contributions to the proton's
magnetic moment, was the first of such experiments and its program has recently
been completed. In this paper we give an overview of some of the experimental
aspects of parity-violating electron scattering, briefly review the theoretical
predictions for strange quark form factors, summarize the SAMPLE measurements,
and place them in context with the program of experiments being carried out at
other electron scattering facilities such as Jefferson Laboratory and the Mainz
Microtron.Comment: 61 pages, review articl
Measurement of the vector analyzing power in elastic electron-proton scattering as a probe of double photon exchange amplitudes
We report the first measurement of the vector analyzing power in inclusive
transversely polarized elastic electron-proton scattering at Q^2 = 0.1
(GeV/c)^2 and large scattering angles. This quantity should vanish in the
single virtual photon exchange, plane wave impulse approximation for this
reaction, and can therefore provide information on double photon exchange
amplitudes for electromagnetic interactions with hadronic systems. We find a
non-zero value of A=-15.4+/-5.4 ppm. No calculations of this observable for
nuclei other than spin 0 have been carried out in these kinematics, and the
calculation using the spin orbit interaction from a charged point nucleus of
spin 0 cannot describe these data.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Today's View on Strangeness
There are several different experimental indications, such as the
pion-nucleon sigma term and polarized deep-inelastic scattering, which suggest
that the nucleon wave function contains a hidden s bar s component. This is
expected in chiral soliton models, which also predicted the existence of new
exotic baryons that may recently have been observed. Another hint of hidden
strangeness in the nucleon is provided by copious phi production in various N
bar N annihilation channels, which may be due to evasions of the
Okubo-Zweig-Iizuka rule. One way to probe the possible polarization of hidden s
bar s pairs in the nucleon may be via Lambda polarization in deep-inelastic
scattering.Comment: 8 pages LaTeX, 10 figures, to appear in the Proceedings of the
International Conference on Parity Violation and Hadronic Structure,
Grenoble, June 200
Parity Violation in Elastic Electron-Proton Scattering and the Proton's Strange Magnetic Form Factor
We report a new measurement of the parity-violating asymmetry in elastic electron scattering from the proton at backward scattering angles. This asymmetry is sensitive to the strange magnetic form factor of the proton as well as electroweak axial radiative corrections. The new measurement of A = -4.92±0.61±0.73 ppm provides a significant constraint on these quantities. The implications for the strange magnetic form factor are discussed in the context of theoretical estimates for the axial corrections
Parity-Violating Interaction Effects I: the Longitudinal Asymmetry in pp Elastic Scattering
The proton-proton parity-violating longitudinal asymmetry is calculated in
the lab-energy range 0--350 MeV, using a number of different, latest-generation
strong-interaction potentials--Argonne V18, Bonn-2000, and Nijmegen-I--in
combination with a weak-interaction potential consisting of rho- and
omega-meson exchanges--the model known as DDH. The complete scattering problem
in the presence of parity-conserving, including Coulomb, and parity-violating
potentials is solved in both configuration- and momentum-space. The predicted
parity-violating asymmetries are found to be only weakly dependent upon the
input strong-interaction potential adopted in the calculation. Values for the
rho- and omega-meson weak coupling constants and
are determined by reproducing the measured asymmetries at 13.6 MeV, 45 MeV, and
221 MeV.Comment: 24 pages, 8 figures, submitted to Physical Review