Pion Production by Neutron Beam

The pion production pn→ppπI D1-I D 1 and pp→ppπI D 10 I D 1 were discussed.The theoretical analysis has been performed by using the models of heavy-meson exchange and pion-rescattering including the effect of nucleon resonances.For all the charge channels，the models work well from the near-threshold(s-wave amplitude)to theΔenergy region(p-wave amplitude)。The pion-production cross sections are decomposed to four independent isospin amplitudes T i D 2 IiIf D 2 which represents the transition from an initial two nucleon state with isospin I I i D 2 i i D 2 to a final state with isospin I I i D 2.The reaction pp→ppπI D 10 I D 1 is characterized by the amplitude T I D 211 I D 2 which is mainly determined by the s-wave I D 2πI D 2 N interaction.Contrary to this，the reaction pn→ppπI D 1-D 1 depends on both the s-wave amplitude T I D 211 D 2 and the p-wave amplitude T I D 201 D 2.The interference between s-and p-wave causes the forward-backward asymmetry of the differential cross section。The recent works with the chiral perturbation theory predict the s-wave amplitude with the opposite sign to the results of the heavy-meson exchange model and the pion-rescattering model because the s-wave amplitude of the chiral perturbation theory changes its sign when going from on-shell to half-off-shell kinematics.However，the models with opposite sign of s-wave fail to explain the angular dependence of pn→ppπI D1-ii D1 reaction。We also discuss about following two topics aboutπI D10个D 1 production.1)The angular distribution is very sensitive to the short range structure ofΔ-excitation mechanism.2)The measurement of analyzing power suggests that large s-wave amplitude is necessary even at higher energy region。

The pion production pn → ppπィイD1-ィエD1 and pp → ppπィイD10ィエD1 were discussed. The theoretical analysis has been performed by using the models of heavy-meson exchange and pion-rescattering including the effect of nucleon resonances. For all the charge channels, the models work well from the near-threshold (s-wave amplitude) to the Δ energy region (p-wave amplitude). The pion-production cross sections are decomposed to four independent isospin amplitudes TィイD2IiIfィエD2 which represents the transition from an initial two nucleon state with isospin IィイD2iィエD2 to a final state with isospin IィイD2fィエD2. The reaction pp → ppπィイD10ィエD1 is characterized by the amplitude TィイD211ィエD2 which is mainly determined by the s-wave ィイD2πィエD2N interaction. Contrary to this, the reaction pn → ppπィイD1-ィエD1 depends on both the s-wave amplitude TィイD211ィエD2 and the p-wave amplitude TィイD201ィエD2. The interference between s- and p-wave causes the forward-backward asymmetry of the differential cross section. The recent works with the chiral perturbation theory predict the s-wave amplitude with the opposite sign to the results of the heavy-meson exchange model and the pion-rescattering model because the s-wave amplitude of the chiral perturbation theory changes its sign when going from on-shell to half-off-shell kinematics. However, the models with opposite sign of s-wave fail to explain the angular dependence of pn → ppπィイD1-ィエD1 reaction. We also discuss about following two topics about πィイD10ィエD1 production. 1) The angular distribution is very sensitive to the short range structure of Δ-excitation mechanism. 2) The measurement of analyzing power suggests that large s-wave amplitude is necessary even at higher energy region.