1. R. Aaij et al. (LHCb Collab.), “Observation of double charm production involving open charm in pp collisions at √s = 7 TeV,” J. High Energy Phys. 06, 141 (2012);
2. Addendum: J. High Energy Phys 03, 108 (2014).
3. R. Aaij et al. (LHCb Collab.), “Production of associated Y and open charm hadrons in pp collisions at √s = 7 and 8 TeV via double parton scattering,” J. High Energy Phys. 07, 052 (2016).
4. J. C. Collins and R. K. Ellis, “Heavy quark production in very high-energy hadron collisions,” Nucl. Phys. B 360, 3—30 (1991).
5. S. Catani and F. Hautmann, “High-energy factorization and small x deep inelastic scattering beyond leading order,” Nucl. Phys. B 427, 475—524 (1994).