366 research outputs found
Measurement of the Proton's Neutral Weak Magnetic Form Factor
We report the first measurement of the parity-violating asymmetry in elastic
electron scattering from the proton. The asymmetry depends on the neutral weak
magnetic form factor of the proton which contains new information on the
contribution of strange quark-antiquark pairs to the magnetic moment of the
proton. We obtain the value n.m. at
(GeV/c).Comment: 4 pages TEX, text available at
http://www.krl.caltech.edu/preprints/OAP.htm
Nucleon Structure and Parity-Violating Electron Scattering
We review the area of strange quark contributions to nucleon structure. In
particular, we focus on current models of strange quark vector currents in the
nucleon and the associated parity-violating elastic electron scattering
experiments from which vector- and axial-vector currents are extractedComment: 40 pages including 7 figures; review article to be published in Int.
J. Mod. Phys.
Precision Measurement of the Radiative Decay of the Free Neutron
The standard model predicts that, in addition to a proton, an electron, and
an antineutrino, a continuous spectrum of photons is emitted in the
decay of the free neutron. We report on the RDK II experiment which measured
the photon spectrum using two different detector arrays. An annular array of
bismuth germanium oxide scintillators detected photons from 14 to 782~keV. The
spectral shape was consistent with theory, and we determined a branching ratio
of 0.00335 0.00005 [stat] 0.00015 [syst]. A second detector array
of large area avalanche photodiodes directly detected photons from 0.4 to
14~keV. For this array, the spectral shape was consistent with theory, and the
branching ratio was determined to be 0.00582 0.00023 [stat] 0.00062
[syst]. We report the first precision test of the shape of the photon energy
spectrum from neutron radiative decay and a substantially improved
determination of the branching ratio over a broad range of photon energies
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
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 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.Comment: 4 pages, 3 figures, submitted to Physical Review Letters, Sept 199
Phenomenology of the Deuteron Electromagnetic Form Factors
A rigorous extraction of the deuteron charge form factors from tensor
polarization data in elastic electron-deuteron scattering, at given values of
the 4-momentum transfer, is presented. Then the world data for elastic
electron-deuteron scattering is used to parameterize, in three different ways,
the three electromagnetic form factors of the deuteron in the 4-momentum
transfer range 0-7 fm^-1. This procedure is made possible with the advent of
recent polarization measurements. The parameterizations allow a
phenomenological characterization of the deuteron electromagnetic structure.
They can be used to remove ambiguities in the form factors extraction from
future polarization data.Comment: 18 pages (LaTeX), 2 figures Feb. 25: minor changes of content and in
Table
Separated Kaon Electroproduction Cross Section and the Kaon Form Factor from 6 GeV JLab Data
The () reaction was studied as a function of
the Mandelstam variable using data from the E01-004 (FPI-2) and E93-018
experiments that were carried out in Hall C at the 6 GeV Jefferson Lab. The
cross section was fully separated into longitudinal and transverse components,
and two interference terms at four-momentum transfers of 1.00, 1.36 and
2.07 GeV. The kaon form factor was extracted from the longitudinal cross
section using the Regge model by Vanderhaeghen, Guidal, and Laget. The results
establish the method, previously used successfully for pion analyses, for
extracting the kaon form factor. Data from 12 GeV Jefferson Lab experiments are
expected to have sufficient precision to distinguish between theoretical
predictions, for example recent perturbative QCD calculations with modern
parton distribution amplitudes. The leading-twist behavior for light mesons is
predicted to set in for values of between 5-10 GeV, which makes data
in the few GeV regime particularly interesting. The dependence at fixed
and of the longitudinal cross section we extracted seems consistent
with the QCD factorization prediction within the experimental uncertainty
Parity-violating Electron Deuteron Scattering and the Proton's Neutral Weak Axial Vector Form Factor
We report on a new measurement of the parity-violating asymmetry in
quasielastic electron scattering from the deuteron at backward angles at Q2=
0.038 (GeV/c)2. This quantity provides a determination of the neutral weak
axial vector form factor of the nucleon, which can potentially receive large
electroweak corrections. The measured asymmetry A=-3.51 +/- 0.57(stat) +/-
0.58(sys)ppm is consistent with theoretical predictions. We also report on
updated results of the previous experiment at Q2=0.091 (GeV/c)2, which are also
consistent with theoretical predictions.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
- …