If the total mass-energy of the initial particle is 128 GeV/c², and energy is conserved in each decay, the total energy is conserved through all decays. The two secondary particles together carry the full 128 GeV/c². Each decays into two photons, resulting in 4 photons total. Since energy is split equally among the photons, each photon has 32 GeV of energy. The total energy remains 128 GeV. - Veritas Home Health