724 research outputs found
Electroexcitation of the P33(1232), P11(1440), D13(1520), S11(1535) at Q^2=0.4 and 0.65(GeV/c)^2
Using two approaches: dispersion relations and isobar model, we have analyzed
recent high precision CLAS data on cross sections of \pi^0, \pi^+, and \eta
electroproduction on protons, and the longitudinally polarized electron beam
asymmetry for p(\vec{e},e'p)\pi^0 and p(\vec{e},e'n)\pi^+. The contributions of
the resonances P33(1232), P11(1440), D13(1520), S11(1535) to \pi
electroproduction and S11(1535) to \eta electroproduction are found. The
results obtained in the two approaches are in good agreement with each other.
There is also good agreement between amplitudes of the \gamma^* N \to S11(1535)
transition found in \pi and \eta electroproduction. For the first time accurate
results are obtained for the longitudinal amplitudes of the P11(1440),
D13(1520) and S11(1535) electroexcitation on protons.Comment: 9 pages, 9 figure
Bulk Mediated Surface Diffusion: Non Markovian Desorption with Finite First Moment
Here we address a fundamental issue in surface physics: the dynamics of
adsorbed molecules. We study this problem when the particle's desorption is
characterized by a non Markovian process, while the particle's adsorption and
its motion in the bulk are governed by a Markovian dynamics. We study the
diffusion of particles in a semi-infinite cubic lattice, and focus on the
effective diffusion process at the interface . We calculate analytically
the conditional probability to find the particle on the plane as well as
the surface dispersion as functions of time. The comparison of these results
with Monte Carlo simulations show an excellent agreement.Comment: 16 pages, 7 figs. European Physical Journal B (in press
A precise extraction of the induced polarization in the 4He(e,e'p)3H reaction
We measured with unprecedented precision the induced polarization Py in
4He(e,e'p)3H at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2. The induced polarization
is indicative of reaction-mechanism effects beyond the impulse approximation.
Our results are in agreement with a relativistic distorted-wave impulse
approximation calculation but are over-estimated by a calculation with strong
charge-exchange effects. Our data are used to constrain the strength of the
spin independent charge-exchange term in the latter calculation.Comment: submitted to Physical Review Letter
Polarization Transfer in the 4He(e,e'p)3H Reaction at Q^2 = 0.8 and 1.3 (GeV/c)^2
Proton recoil polarization was measured in the quasielastic 4He(e,e'p)3H
reaction at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision.
The polarization-transfer coefficients are found to differ from those of the
1H(e,e' p) reaction, contradicting a relativistic distorted-wave approximation,
and favoring either the inclusion of medium-modified proton form factors
predicted by the quark-meson coupling model or a spin-dependent charge-exchange
final-state interaction. For the first time, the polarization-transfer ratio is
studied as a function of the virtuality of the proton
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
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