Observation of double charm production involving open charm in pp collisions at √s=7 TeV - Aaij,R; Abellan,Beteta C; Adeva,B; Adinolfi,M; Adrover,C; Affolder,A; Ajaltouni,Z; Albrecht,J; Alessio,F; Alexander,M; Ali,S; Alkhazov,G; et al. (JOURNAL OF HIGH ENERGY PHYSICS, 2012)