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Register a new userOn the different role of protons and neutrons in antinucleon annihilations on nuclei
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We compare data of antineutron and antiproton annihilation cross sections on different targets at very low energies. After subtracting Coulomb effects, we observe that the ratio between the antineutron proton and antiproton proton annihilation cross sections is an oscillating function of the energy at momenta smaller 300 MeV/c. This nontrivial behavior is confirmed by the analysis of the relative number of antiproton-neutron and antiproton-proton annihilations in nuclei. We show that a part of the strong shadowing phenomena in antiproton-nucleus annihilations can be explained in terms of this oscillation, while a part requires different explainations.
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Here a short synthesis is presented of the work, developed in the last two years by the Brescia Collaboration, on the phenomenology of antinucleon-nucleon and antinucleon-nucleus annihilation at small momenta (below 300 MeV/c in the laboratory), with special stress on the role of general principles.
We show that the quantum uncertainty principle puts some limits on the effectiveness of the antinucleon-nucleus annihilation at very low energies. This is caused by the fact that the realization a very effective short-distance reaction process implies information on the relative distance of the reacting particles. Some quantitative predictions are possible on this ground, including the approximate A-independence of antinucleon-nucleus annihilation rates.
For the first time, the total yield and inclusive spectra of the $Delta^{++}(1232)$isobar are measured in $ u p$ and $ u n$ charged-current interactions. An indication is obtained that the $Delta^{++}(1232)$ production mainly results from the neutrino scattering on the valence d- quark of the target nucleon. The total yield of $Delta^{++}(1232)$ in $ u p$ interactions is compatible with that measured in hadronic interactions of the same net charge and net baryonic number. The yield of $Delta^{++}(1232)$ in $ u n$ interactions is significantly suppressed as compared to the case of the proton target. The form of the squared transverse momentum distributions, both in $ u p$ and $ u n$ interactions, is found to be compatible with the available data on the neutrinoproduction of $Lambda$ hyperon. The experimental data are compared with the LEPTO6.5 model predictions.
Experimental above-barrier fusion cross-sections for $^{17}$F + $^{12}$C are compared to the fusion excitation functions for $^{16,18}$O, $^{19}$F, and $^{20}$Ne ions on a carbon target. In comparing the different systems both the differing static size of the incident ions and changes in fusion barrier are accounted for by examining the reduced fusion cross-section. Remaining trends of the fusion cross-section above the barrier which reflect the sensitive interplay of the sd protons and neutrons are observed. The experimental data are also compared to both a widely-used analytical model of near-barrier fusion, as well as a time-dependent Hartree-Fock model. Both models fail to describe the trends observed.
We calculate, in a systematic way, the enhancement effect on antiproton-proton and antiproton-nucleus annihilation cross sections at low energy due to the initial state electrostatic interaction between the projectile and the target nucleus. This calculation is aimed at future comparisons between antineutron and antiproton annihilation rates on different targets, for the extraction of pure isospin channels.
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