464 research outputs found
New Measurements of the Transverse Beam Asymmetry for Elastic Electron Scattering from Selected Nuclei
We have measured the beam-normal single-spin asymmetry An in the elastic scattering of 1-3 GeV transversely polarized electrons from H-1 and for the first time from He-4, C-12, and Pb-208. For H-1, He-4, and C-12, the measurements are in agreement with calculations that relate A(n) to the imaginary part of the two-photon exchange amplitude including inelastic intermediate states. Surprisingly, the Pb-208 result is significantly smaller than the corresponding prediction using the same formalism. These results suggest that a systematic set of new A(n) measurements might emerge as a new and sensitive probe of the structure of heavy nuclei
Precision Measurement of the Proton and Deuteron Spin Structure Functions g\u3csub\u3e2\u3c/sub\u3e and Asymmetries A\u3csub\u3e2\u3c/sub\u3e
We have measured the spin struction functions g2(p) and g(2)(d) and the virtual photon asymmetries A(2)(p) and A(2)(d) over the kinetmatic range 0.02 less than or equal to x less than or equal to 0.8 and 0.7 less than or equal to Q2 less than or equal to 20 GeV2 by scattering 29.1 and 32.3 GeV longitudinally polarized electrons from transversely polarized NH3 and (LiD)-Li-6 targets. Our measured g2 approximately follows the twist-2 Wandzura-Wilczek calculation. The twist-3 reduced matrix elements d(2)(p) and d(2)(n) are less than two standard deviations from zero. The data are inconsistent with the Burkhardt-Cottingham sum rule if there is no pathological behavior as x --\u3e 0. The Efremov-Leader-Teryaev integral is consistent with zero within our measured kinematic range. The absolute value of A2 is significantly smaller than the A2 \u3c â R(1 +A1)/2 limit
Qweak: A Precision Measurement of the Proton's Weak Charge
The Qweak experiment at Jefferson Lab aims to make a 4% measurement of the
parity-violating asymmetry in elastic scattering at very low of a
longitudinally polarized electron beam on a proton target. The experiment will
measure the weak charge of the proton, and thus the weak mixing angle at low
energy scale, providing a precision test of the Standard Model. Since the value
of the weak mixing angle is approximately 1/4, the weak charge of the proton
is suppressed in the Standard Model, making it
especially sensitive to the value of the mixing angle and also to possible new
physics. The experiment is approved to run at JLab, and the construction plan
calls for the hardware to be ready to install in Hall C in 2007. The
theoretical context of the experiment and the status of its design are
discussed.Comment: 5 pages, 2 figures, LaTeX2e, to be published in CIPANP 2003
proceeding
Inclusive Electron-Nucleus Scattering at Large Momentum Transfer
Inclusive electron scattering is measured with 4.045 GeV incident beam energy
from C, Fe and Au targets. The measured energy transfers and angles correspond
to a kinematic range for Bjorken and momentum transfers from . When analyzed in terms of the y-scaling function the data show
for the first time an approach to scaling for values of the initial nucleon
momenta significantly greater than the nuclear matter Fermi-momentum (i.e. GeV/c).Comment: 5 pages TEX, 5 Postscript figures also available at
http://www.krl.caltech.edu/preprints/OAP.htm
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
Measurement of GEp/GMp in ep -> ep to Q2 = 5.6 GeV2
The ratio of the electric and magnetic form factors of the proton, GEp/GMp,
was measured at the Thomas Jefferson National Accelerator Facility (JLab) using
the recoil polarization technique. The ratio of the form factors is directly
proportional to the ratio of the transverse to longitudinal components of the
polarization of the recoil proton in the elastic
reaction. The new data presented in this article span the range 3.5 < Q2 < 5.6
GeV2 and are well described by a linear Q2 fit. Also, the ratio QF2p/F1p
reaches a constant value above Q2=2 GeV2.Comment: 6 pages, 4 figures Added two names to the main author lis
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-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
Cross Section Measurement of Charged Pion Photoproduction from Hydrogen and Deuterium
We have measured the differential cross section for the gamma n --> pi- p and
gamma p --> pi+ n reactions at center of mass angle of 90 degree in the photon
energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at photon
energies greater than 3.3 GeV exhibit a global scaling behavior for both pi-
and pi+ photoproduction, consistent with the constituent counting rule and the
existing pi+ photoproduction data. Possible oscillations around the scaling
value are suggested by these new data The data show enhancement in the scaled
cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio
of exclusive pi- to pi+ photoproduction at high energy is consistent with the
prediction based on one-hard-gluon-exchange diagrams
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