415 research outputs found
Coherent π^0 photoproduction on the deuteron up to 4 GeV
The differential cross section for ^2H(γ,d)π^0 has been measured at deuteron center-of-mass angles of 90° and 136°. This work reports the first data for this reaction above a photon energy of 1 GeV, and permits a test of the apparent constituent counting rule and reduced nuclear amplitude behavior as observed in elastic ed scattering. Measurements were performed up to a photon energy of 4.0 GeV, and are in good agreement with previous lower energy measurements. Overall, the data are inconsistent with both constituent-counting rule and reduced nuclear amplitude predictions
Quantifying Rapid Variability in Accreting Compact Objects
I discuss some practical aspects of the analysis of millisecond time
variability X-ray data obtained from accreting neutron stars and black holes.
First I give an account of the statistical methods that are at present commonly
applied in this field. These are mostly based on Fourier techniques. To a large
extent these methods work well: they give astronomers the answers they need.
Then I discuss a number of statistical questions that astronomers don't really
know how to solve properly and that statisticians may have ideas about. These
questions have to do with the highest and the lowest frequency ranges
accessible in the Fourier analysis: how do you determine the shortest time
scale present in the variability, how do you measure steep low-frequency noise.
The point is stressed that in order for any method that resolves these issues
to become popular, it is necessary to retain the capabilities the current
methods already have in quantifying the complex, concurrent variability
processes characteristic of accreting neutron stars and black holes.Comment: To be published in the Proceedings of "Statistical Challenges in
Modern Astronomy II", University Park PA, USA, June 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
Longitudinal-Transverse Separations of Structure Functions at Low for Hydrogen and Deuterium
We report on a study of the longitudinal to transverse cross section ratio,
, at low values of and , as determined from
inclusive inelastic electron-hydrogen and electron-deuterium scattering data
from Jefferson Lab Hall C spanning the four-momentum transfer range 0.06 GeV. Even at the lowest values of , remains
nearly constant and does not disappear with decreasing , as expected. We
find a nearly identical behaviour for hydrogen and deuterium.Comment: 4 pages, 2 gigure
A precise measurement of the deuteron elastic structure function A(Q^2)
The A(Q^2) structure function in elastic electron-deuteron scattering was
measured at six momentum transfers Q^2 between 0.66 and 1.80 (GeV/c)^2 in Hall
C at Jefferson Laboratory. The scattered electrons and recoil deuterons were
detected in coincidence, at a fixed deuteron angle of 60.5 degrees. These new
precise measurements resolve discrepancies between older sets of data. They put
significant constraints on existing models of the deuteron electromagnetic
structure, and on the strength of isoscalar meson exchange currents.Comment: 3 LaTeX pages plus 2 PS figure
Measurement of the 12C(e,e'p)11B Two-Body Breakup Reaction at High Missing Momentum Values
The five-fold differential cross section for the 12C(e,e'p)11B reaction was
determined over a missing momentum range of 200-400 MeV/c, in a kinematics
regime with Bjorken x > 1 and Q2 = 2.0 (GeV/c)2. A comparison of the results
and theoretical models and previous lower missing momentum data is shown. The
theoretical calculations agree well with the data up to a missing momentum
value of 325 MeV/c and then diverge for larger missing momenta. The extracted
distorted momentum distribution is shown to be consistent with previous data
and extends the range of available data up to 400 MeV/c.Comment: 12 pages, 1 table and 3 figures for submission to Journal Physics
Determination of the pion charge form factor for Q^2=0.60-1.60 GeV^2
The data analysis for the reaction H(e,e' pi^+)n, which was used to determine
values for the charged pion form factor Fpi for values of Q^2=0.6-1.6 GeV^2,
has been repeated with careful inspection of all steps and special attention to
systematic uncertainties. Also the method used to extract Fpi from the measured
longitudinal cross section was critically reconsidered. Final values for the
separated longitudinal and transverse cross sections and the extracted values
of Fpi are presented.Comment: 11 pages, 6 figure
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