Subdominant terms in the production of cc pairs in proton-proton collisions

At high energies the gluon-gluon fusion is the dominant mechanism of cc production. This process was calculated in the next-to-leading-order collinear as well as in the kt-factorization approaches in the past. We show that the present knowledge of gluon distributions does not allow one to make precise predictions for cc production at LHC, in particular at forward rapidities. In this paper we study production of cc pairs including several subleading mechanisms. This includes gg→QQ, γg→QQ, gγ→QQ, and γγ→QQ. In this context we use Martin-Roberts-Stirling-Thorne QED parton distributions which include the 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. 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 the distribution in c (c) rapidity and transverse momentum. Finally, we present results for an 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.