Study of muon pair production from positron annihilation at threshold energy. (1st January 2020) - Amapane, N.; Antonelli, M.; Anulli, F.; Ballerini, G.; Bandiera, L.; Bartosik, N.; Bauce, M.; Bertolin, A.; Biino, C.; Blanco-Garcia, O.R.; Boscolo, M.; Brizzolari, C.; et al.