J=ψ-meson production within improved color evaporation model with the kT-factorization approach for c(c)over-bar production

We use a new approach for the color evaporation model for quarkonium production. The production of c (c) over bar pairs is performed within the k(T)-factorization approach using different unintegrated gluon distribution functions (UGDF) from the literature. We include all recent improvements to the color evaporation model. We cannot describe simultaneously midrapidity and forward rapidity data measured at the LHC when using the Kimber-Martin-Ryskin (KMR) UGDF based on the collinear MMHT2014lo parton distribution function (PDF) with the same normalization parameter. Furthermore, we get a somewhat too hard distribution in the J/psi transverse momentum. Correcting the standard KMR-MMHT2014lo distributions for saturation effects at small values of x improves J/psi rapidity distributions. When using CT14lo collinear PDFs a better agreement with the LHCb data can be achieved without a clear need for implementing saturation effects. We get a poor description of the large transverse momentum distributions of J/psi with the JH-2013 Ciafaloni-Catani-Fiorani-Marchesini (CCFM)-based UGDF. Here an explicit inclusion of the 2 -> 3 processes considerably improves the situation. Similar effects are discussed in the context of the KMR UGDF.