35 research outputs found
Total Hadronic Cross Section Data and the Froissart-Martin Bound
The energy dependence of the total hadronic cross section at high energies is
investigated with focus on the recent experimental result by the TOTEM
Collaboration at 7 TeV and the Froissart-Martin bound. On the basis of a class
of analytical parametrization with the exponent in the leading
logarithm contribution as a free parameter, different variants of fits to
and total cross section data above 5 GeV are developed. Two
ensembles are considered, the first comprising data up to 1.8 TeV, the second
also including the data collected at 7 TeV. We shown that in all fit variants
applied to the first ensemble the exponent is statistically consistent with
= 2. Applied to the second ensemble, however, the same variants yield
's above 2, a result already obtained in two other analysis, by U.
Amaldi \textit{et al}. and by the UA4/2 Collaboration. As recently discussed by
Ya. I. Azimov, this faster-than-squared-logarithm rise does not necessarily
violate unitarity. Our results suggest that the energy dependence of the
hadronic total cross section at high energies still constitute an open problem.Comment: 20 pages, 10 figures, introduction extended and general references
added to match editorial style, to appear in the Brazilian Journal of Physic
Changes to the Fossil Record of Insects through Fifteen Years of Discovery
The first and last occurrences of hexapod families in the fossil record are compiled from publications up to end-2009. The major features of these data are compared with those of previous datasets (1993 and 1994). About a third of families (>400) are new to the fossil record since 1994, over half of the earlier, existing families have experienced changes in their known stratigraphic range and only about ten percent have unchanged ranges. Despite these significant additions to knowledge, the broad pattern of described richness through time remains similar, with described richness increasing steadily through geological history and a shift in dominant taxa, from Palaeoptera and Polyneoptera to Paraneoptera and Holometabola, after the Palaeozoic. However, after detrending, described richness is not well correlated with the earlier datasets, indicating significant changes in shorter-term patterns. There is reduced Palaeozoic richness, peaking at a different time, and a less pronounced Permian decline. A pronounced Triassic peak and decline is shown, and the plateau from the mid Early Cretaceous to the end of the period remains, albeit at substantially higher richness compared to earlier datasets. Origination and extinction rates are broadly similar to before, with a broad decline in both through time but episodic peaks, including end-Permian turnover. Origination more consistently exceeds extinction compared to previous datasets and exceptions are mainly in the Palaeozoic. These changes suggest that some inferences about causal mechanisms in insect macroevolution are likely to differ as well