Observation of double charm production involving open charm in pp collisions at root s=7 TeV

The production of J/psi mesons accompanied by open charm, and of pairs of open charm hadrons are observed in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 355 pb(-1) collected with the LHCb detector. Model independent measurements of absolute cross-sections are given together with ratios to the measured J/psi and open charm cross-sections. The properties of these events are studied and compared to theoretical predictions.