New single- and double-parton scattering mechanisms for double charmed meson production

We discuss charm meson-meson pair production recently observed by the LHCb Collaboration at $\sqrt{s}$ = 7 TeV in proton-proton scattering. We examine double-parton scattering (DPS) mechanisms of double $c\bar{c}$ production and following $cc\to D^0{D}^0$ hadronization as well as double $g$ and mixed $g c\bar c $productionwith$gg \to D^{0}D^{0}$and$gc \to D^{0}D^{0}$ hadronization calculated with the help of the scale-dependent KKKS08 fragmentation functions. A new single-parton scattering (SPS) mechanism of $gg$ production is also taken into consideration. Calculated differential distributions as a function of transverse momentum $p_T$ of one of the $D^0$ mesons, pair invariant mass $M_{D^0{D}^0}$ and azimuthal angle ${\phi }_{D^0{D}^0}$ distributions are confronted with the measured ones. The manifestation of the new SPS mechanisms with $g\to D^0$ fragmentation within the scale-dependent fragmentation scheme change the overall picture suitable for standard scale-independent fragmentation where only DPS $cc\to D^0{D}^0$ mechanism is present. Some consequences of the new mechanisms are discussed