Isoscalar off-shell effects in threshold pion production frompdcollisions

Abstract

We test the presence of pion-nucleon isoscalar off-shell effects in the pd → π + t reaction around the threshold region. We find that these effects significantly modify the production cross section and that they may provide the missing strength needed to reproduce the data at threshold. PACS numbers(s): 25.10.+s, 25.40.Qa, 13.75.Gx

Spin observables for pion production from pd collisions

“…With the same parameterization suggested by Hamilton we found in Ref. [1] that the pionproduction cross section at threshold can be reproduced, while without these off-shell effects the results are underestimated by one order of magnitude.…”

“…With the same model of Ref. [1], we have calculated the spin observables at threshold. The formalism for the spin observables for this reaction has been given in Ref.…”

“…In a recent paper [1], the π-production reaction from pd collisions has been calculated in the threshold region. The model includes meson-exchange rescattering diagrams in s waves, with πN contributions in the isovector and the isoscalar channels.…”

Positive pion absorption on3Heusing modern trinucleon wave functions

“…New experiments are also performed or in progress on meson production in few-nucleon systems as in pd → 3 He π 0 or pd → 3 H π + [7] as well as corresponding η meson production experiments [8]. However, theoretical efforts in this direction with three-nucleon dynamics are very scarce [9,10] and the situation is much less satisfactory as compared with the two-nucleon case. Nevertheless, pionic inelasticities in 3-or 4-nucleon systems should be the necessary bridge towards understanding them in nuclei and potentially using them as a probe in many-body nuclear physics and for possible effects of nuclear medium on hadrons and their interactions.…”

Why is the three-nucleon force so odd?

“…A coupled-channel calculation with the explicit treatment of the ∆-isobar excitation which leads to effective 3N F 's in the three-nucleon subsystem reduces the Sagara discrepancy by a considerably large fraction [6]. Useful insights about the importance of possible 3N F -diagrams should also be obtained from the study of pion production/absorption mechanisms in the 3N system, since progress has been recently made in the theoretical treatment of these reactions at the ∆ resonance [7,8] and in the threshold region [9].…”