The LHCb collaboration has recently measured cross sections for the simultaneous production of two charmed-particles in p-p  and p-Pb  collisions. These include opposite-sign and same-sign D-meson pairs offering, for the first time, a chance to study the interplay of single-parton (SPS) and double-parton scattering (DPS) across different collision systems.
In this talk, we discuss our NLO QCD framework  used to calculate the double D-meson cross sections. The setup is based on factorized PDFs and D-meson fragmentation functions, taking into into account both the SPS and DPS contributions. The DPS contributions are estimated with an effective cross section approach neglecting the partonic correlations. We find a nice agreement with the LHCb p-p and p-Pb data when using values for the effective cross section consistent with other measurements. In particular, we conclude that the same-sign D-meson data provide the first quantitative confirmation of DPS at work in p-Pb collisions.
We also compare our results to Pythia Monte Carlo simulations and discuss the implications of DPS on the two-particle azimuthal correlations and possibilities to resolve signatures of saturation phenomena.
 LHCb Collaboration, JHEP 06 (2012) 141.
 LHCb Collaboration, arXiv:2007.06945 [hep-ex].
 Helenius, Paukkunen, Phys.Lett.B 800 (2020) 135084.