Aaij, R., Adeva, B., Adinolfi, M., Adrover, C., Affolder, A., Ajaltouni, Z., et al. (2012). Observation of J/psi-pair production in pp collisions at root s=7 TeV. Physics Letters B, 707(1), 52-59. doi:10.1016/j.physletb.2011.12.015.