The (π−,γγ) reaction in nuclei and the σ meson in the medium Original Research Article

A theoretical analysis of the (π−,γγ) reaction in nuclei is made in order to find the viability of this reaction to test modifications of the σ meson mass in nuclear matter. The ππ correlation in the scalar–isoscalar channel in nuclear matter could, in principle, manifest itself in this reaction since it plays an important role in the ππ→γγ mechanism. But we conclude that this effect is hardly visible in this reaction due to the strong background of the pion-bremsstrahlung terms. Only with some special cuts and for some polarization states are the effect visible at the cost of a strong reduction in the cross section.