New mechanisms for double charmed meson production at the LHCb

Abstract

We discuss production of $D^0{D}^0$ (and ${\bar{D}}^0{\bar{D}}^0$) pairs related to the LHCb Collaboration results for $\sqrt{s}$ = 7 TeV in proton-proton scattering. We consider double-parton scattering (DPS) mechanisms of double $c\bar{c}$ production and subsequent $cc\to D^0{D}^0$ hadronization as well as double $g$ and mixed $gc\bar{c}$ production with $gg\to D^0{D}^0$ and $gc\to D^0{D}^0$ hadronization calculated with the help of the scale-dependent hadronization functions of Kniehl et al. Single-parton scattering (SPS) mechanism of digluon production is also taken into account. We compare our results with several correlation observables in azimuthal angle ${\phi }_{D^0{D}^0}$ between $D^0$ mesons or in dimeson invariant mass $M_{D^0{D}^0}$. The inclusion of new mechanisms with $g\to D^0$ fragmentation leads to larger cross sections, than when including only DPS mechanism with standard scale-independent $cc\to D^0{D}^0$ fragmentation functions. Some consequences of the presence of the new mechanisms are discussed. In particular a larger ${\sigma }_{eff}$ is needed to describe the LHCb data. There is a signature that ${\sigma }_{eff}$ may depend on transverse momentum of $c$ quarks and/or $\bar{c}$ antiquarks.

Comments: 16 pages, 6 figures