In 1959, B. Pontecorvo proposed an experimental idea to establish whether v e and v are

In 1959, B. Pontecorvo proposed an experimental idea to establish whether v̅_e and v̅_μ are different particles or not. To produce v̅_μ, a low-energy π⁺ beam is brought to rest in a target. The μ⁺s from their decays come to rest too and then decay.

(1) What is the lowest energy-threshold reaction that would be permitted if ν̅_e = ν̅_μ but forbidden if ν̅_e ≠ ν̅_μ?

(2) What is its energy threshold?

(3) Does the considered process provide any ν̅_μ above threshold?