6533b85ffe1ef96bd12c1e30

RESEARCH PRODUCT

Coherent two pion photoproduction on C-12

S.s. KamalovEulogio Oset

subject

PhysicsNuclear and High Energy PhysicsParticle physicsNuclear TheoryMesonNuclear TheoryFOS: Physical sciencesFísicaSymmetry (physics)Nuclear Theory (nucl-th)RenormalizationPionIsospinIsobarProduction (computer science)High Energy Physics::ExperimentNuclear ExperimentExcitation

description

We develop the formalism for coherent two pion photoproduction in nuclei and perform actual calculations of cross sections for $\pi^-\pi^+$ and $\pi^0\pi^0$ photoproduction on $^{12}C$. We find that due to the isospin symmetry the cross section for $\pi^0\pi^0$ production is very small and has a maximum when the pions propagate together. However, the kinematical region where the energies and polar angles of the two $\pi^0$ mesons are equal and their relative azimuthal angle $\phi=180^0$ is forbidden. Conversely in the $\pi^-\pi^+$ production the pions prefer to have a relative azimuthal angle 180$^0$ and the production of the pions propagating together is suppressed. The dominant one-body mechanism in both channels is related to the excitation of the $\Delta$ isobar. Hence the reaction can serve as a source of information about $\Delta$'s properties in nucleus. We have found that the reaction is sensitive to effects of the pion and $\Delta$ renormalization in the nuclear medium, similar to those found in the coherent $(\gamma,\pi^0)$ reaction, but magnified because of the presence of the two pions.

10.1016/s0375-9474(97)00372-2http://hdl.handle.net/10550/46861