Observation ofJ/ψ-pair production in pp collisions ats=7TeV - Aaij,R; Adeva,B; Adinolfi,M; Adrover,C; Affolder,A; Ajaltouni,Z; Albrecht,J; Alessio,F; Alexander,M; Alkhazov,G; Alvarez,Cartelle P; Alves,AA; et al. (Physics Letters B, 2012)