Pion absorption cross section for2H and3He in theΔ-isob

Abstract

The absorption of π + on 3 He in the ∆-region is evaluated with exact inclusion of the final state interaction among the three emerging protons. The absorption is described by a πN → ∆ vertex and a N ∆-N N transition t-matrix which are calculated from a phenomenological model for N N and πd reactions. In a calculation where the initial pion scattering effects are neglected, the predicted peaks of the pion absorption cross sections for 2 H and 3 He lie too high in energy in relation to the data. The effect of the final state three-nucleon interaction turns out to be too small for changing the magnitude and shifting the peak position of the total absorption cross section for 3 He. We demonstrate that the adjustment of the peak position for the deuteron cross section by small modifications of the ∆-parameters, automatically leads to the correct peak position in 3 He. 25.10.+x, 25.80.Ls

Hidden dibaryons in one- and two-pion production in NN collisions

“…We found that the conventional ONE + N∆ mechanisms with the mesonbaryon vertices parameterized in the form (19)-(20) using the parameters Λ = 0.7 andΛ * = 0.3 GeV (corresponding to the monopole parameters Λ = 0.7 and Λ * = 0.44 GeV) give about half the experimental cross section in the 1 D 2 P partial wave and also about half the total cross section near their maximal values (at √ s ≃ 2.14-2.16 GeV), with a theoretical peak shifted by about 20 MeV to the right relatively to its experimental position. It is worth noting that quite similar results were obtained previously in the works [24,92].…”

Meson-exchangeπNmodels in three-dimensional Bethe-Salpeter formulation

“…Despite very extensive investigations in the past two decades, several outstanding problems remain to be solved. For example, an accurate description of pion absorption by nuclei [1,2,3,4,5] is still not available and hence the very extensive data for pion-nucleus reactions and pion productions from relativistic heavy-ion collisions have not been understood satisfactorily. To make progress, it is necessary to improve our theoretical description of the πN off-shell amplitude which is the basic input to most of the existing nuclear calculations at intermediate energies.…”

Isoscalar off-shell effects in threshold pion production frompdcollisions

“…The addition of just one nucleon increases the complexity of the reaction which involves now the simplest nontrivial multinucleon system where it is possible to test the fundamental N N → πN N process and, at the same time, to solve the accurately the nuclear dynamics with Faddeev methods. Applications of Faddeev methods to pion production/absorption started very recently with studies centered around the ∆ resonance [14,15] and herein we apply the same technique of Ref. [15] to study pion production at threshold.…”