7 research outputs found
Electromagnetic Dissociation of Nuclei in Heavy-Ion Collisions
Large discrepancies have been observed between measured Electromagnetic
Dissociation(ED) cross sections and the predictions of the semiclassical
Weiz\"acker-Williams-Fermi(WWF) method. In this paper, the validity of the
semiclassical approximation is examined. The total cross section for
electromagnetic excitation of a nuclear target by a spinless projectile is
calculated in first Born approximation, neglecting recoil. The final result is
expressed in terms of correlation functions and convoluted densities in
configuration space. The result agrees with the WWF approximation to leading
order(unretarded electric dipole approximation), but the method allows an
analytic evaluation of the cutoff, which is determined by the details of the
electric dipole transition charge density. Using the Goldhaber-Teller model of
that density, and uniform charge densities for both projectile and target, the
cutoff is determined for the total cross section in the nonrelativistic limit,
and found to be smaller than values currently used for ED calculations. In
addition, cross sections are calculated using a phenomenological momentum space
cutoff designed to model final state interactions. For moderate projectile
energies, the calculated ED cross section is found to be smaller than the
semiclassical result, in qualitative agreement with experiment.Comment: 28 page
B_c meson production in \gamma\gamma collisions and charm content of the photon
Based on photon structure function formalism we have calculated
meson production cross section in collisions via
partonic subprocess . It was shown that this
approach gives the same results for meson cross sections as the
direct leading order QCD calculation of the subprocess at small energy. Howere, opposite to the direct QCD
calculation we have obtained the increase of the meson cross
section at large energies. We have found also additional contribution to the
meson production via the nonperturbative fluctuations
.Comment: LaTeX, 7 pages and 6 figures available upon reques
The origins and abundances of the chemical elements before 1957: from Prout's hypothesis to Pasadena
The 1957 papers by Burbidge, Burbidge, Fowler, and Hoyle and by Cameron are generally
regarded as the foundations upon which our modern understanding of nucleosynthesis has
been erected. They were, however, also the capstones of an extended period of
investigation of the composition of the cosmos (earth, sun, and beyond) and of the
processes that might have given rise to that composition, dating back at least as far as
1885, that is longer before 1957 than “now” is after 1957