We explore the photoproduction mechanisms for charged and neutral pion pairs off a heavy nucleus at threshold. We calculate the production of charged pairs in the Coulomb field of the nucleus in the Born approximation using explicit expressions for the differential cross sections and their connection with the total cross section $\sigma (\gamma \gamma \to {\pi }^{+}{\pi }^{-})$. The production of $\sigma$ mesons at threshold and their subsequent decay into pions is an important mechanism and is investigated quantitatively in a framework that can be used for both charged and neutral pions. $\sigma$ mesons can be produced via electromagnetic (photon exchange) or strong ($\omega$ exchange) interactions. For neutral pions, another production mechanism consists of the two-step process where charged pions are produced first and then charge exchange into two neutral pions. Differential and total cross sections are computed for each production mechanism.

• Received 9 March 2022
• Accepted 16 May 2022

DOI:https://doi.org/10.1103/PhysRevC.105.065202