Nuclear fragmentation and charge-exchange reactions induced by pions in the $\mathrm{\Delta }\text{-resonance}$ region

The dynamics of the nuclear fragmentations and the charge exchange reactions in pion-nucleus collisions near the $\mathrm{\Delta }$(1232) resonance energies has been investigated within the Lanzhou quantum molecular dynamics transport model. An isospin-, momentum-, and density-dependent pion-nucleon potential is implemented in the model, which influences the pion dynamics, in particular the kinetic energy spectra, but weakly impacts the fragmentation mechanism. The absorption process in pion-nucleon collisions to form the $\mathrm{\Delta }$(1232) resonance dominates the heating mechanism of the target nucleus. The excitation energy transferred to the target nucleus increases with the pion kinetic energy and is similar for both ${\pi }^{-}-$ and ${\pi }^{+}\text{-induced}$ reactions. The magnitude of fragmentation of the target nucleus weakly depends on the pion energy. The isospin ratio in the pion double-charge exchange is influenced by the isospin ingredient of target nucleus.

Figure 1

Momentum and density dependence of the pion optical potential in dense nuclear matter with the isospin asymmetry of $\delta =0.2$.

Figure 2

The elastic (upper panels) and total (lower panels) pion-nucleon scattering cross sections contributed from different resonances. The available data are taken from the PDG Collaboration [28].

Figure 3

Kinetic energy spectra of ${\pi }^{-}, {\pi }^0$, and ${\pi }^{+}$ produced in collisions of ${\pi }^{-}$ and ${\pi }^{+}$ on ${}^{40}\mathrm{Ca}$ at an incident momentum of 300 $\mathrm{MeV}/c$ without (red lines) and with (blue lines) the pion-nucleon potentials, respectively.

Figure 4

The same as in Fig. 3, but for the target of ${}^{197}\mathrm{Au}$ at an incident kinetic energy of 180 MeV.

Figure 5

Rapidity and transverse momentum distributions of ${\pi }^{-}, {\pi }^0$, and ${\pi }^{+}$ produced in pion-induced reactions at the incident momentum of 300 $\mathrm{MeV}/c$.

Figure 6

Kinetic energy spectra of pions at an outgoing angle of ${80}^{\circ }$ in double-charge exchange reactions at an incident energy of 180 MeV. The available data are from the LAMPF measurements [30].

Figure 7

Rapidity and kinetic energy distributions of fragments with a charge number of $Z\ge 2$ in collisions of ${\pi }^{-}$ and ${\pi }^{+}$ on ${}^{40}\mathrm{Ca}$ at an incident momentum of 300 $\mathrm{MeV}/c$, respectively.

Figure 8

The same as in Fig. 5, but for the target of ${}^{197}\mathrm{Au}$ at an incident kinetic energy of 180 MeV.

Figure 9

Mass and charge distributions of fragments produced in collisions of ${\pi }^{-}$ and ${\pi }^{+}$ on ${}^{40}\mathrm{Ca}$ at the incident momentum of 300 MeV/c, respectively.

Figure 10

Fragment distributions with and without the pion-nucleon potential in the ${\pi }^{-}+{}^{197}\mathrm{Au}$ reaction at incident energy of 100 MeV, 180 MeV and 300 MeV, respectively. The available data are from the LAMPF measurements [11].

Figure 11

The same as in Fig. 8, but for the reaction of ${\pi }^{+}+{}^{197}\mathrm{Au}$.

Figure 12

Correlation of the IMFs and charged-particle multiplicity in collisions of ${\pi }^{\pm }+{}^{197}\mathrm{Au}$ at incident energies of 100, 180, and 300 MeV, respectively.