Restoration of Isospin Symmetry in Highly Excited Nuclei

Explicit relations between the isospin mixing probability, the spreading width $\Gamma_{IAS}^{\downarrow}$ of the Isobaric Analog State (IAS) and the statistical decay width $\Gamma_c$ of the compound nucleus at finite excitation energy, are derived by using the Feshbach projection formalism. The temperature dependence of the isospin mixing probability is discussed quantitatively for the first time by using the values of $\Gamma_{IAS}^{\downarrow}$ and of $\Gamma_c$ calculated by means of microscopic models. It is shown that the mixing probability remains essentially constant up to a temperature of the order of 1 MeV and then decreases to about 1/4 of its zero temperature value, at higher temperature than $\approx$ 3 MeV, due to the short decay time of the compound system.Comment: 13 pages, 1 figure (PostScript file included). To appear in Phys. Lett.

Minimal Stereoscopic Analysis for Imaging Atmospheric Cherenkov Telescope Arrays

The trajectory of a primary gamma-ray detected with an array of at least four atmospheric Cherenkov imaging telescopes can be reconstructed from the shower image centroid positions and geometrical considerations independent of the primary energy. Using only the image centroid positions some cosmic-ray discrimination is also possible. This minimal approach opens the possibility of pushing the analysis threshold to lower values, close to the hardware threshold