Diffractive production of c \bar c
  At high-energies the gluon-gluon fusion is the dominant mechanism of c \bar c production. This process was calculated in the NLO collinear as well as in the kt-factorization approaches in the past. In this presentation we concentrate on production of c \bar c pairs including several subleading mechanisms. In this context we use MRST-QED parton distributions which include photon as a parton in the proton as well as elastic photon distributions calculated in the equivalent photon approximation. We present distributions in the c quark (c antiquark) rapidity and transverse momenta and compare them to the dominant gluon-gluon fusion contribution.valent photon approximation. We discuss also inclusive single and central diffractive processes using diffractive parton distribution found from the analysis of HERA diffractive data. As in the previous case we present distribution in c \bar c rapidity and transverse momentum. Next we present results for exclusive central diffractive mechanism discussed recently in the literature. We show corresponding differential distributions and compare them with corresponding distributions for single and central diffractive components. Finally we discuss production of two pairs of c \bar c within a simple formalism of double-parton scattering (DPS). Surprisingly very large cross sections, comparable to single-parton scattering (SPS) contribution, are predicted for LHC energies. 
Marta Luszczak, Rafal Maciula, Antoni Szczurek
hep-ph