Role of initial gluon emission in double J/ψ production at central rapidities

We consider the process of double J/psi production in pp collisions at the LHC in the framework of the k(T)-factorization approach. We focus on the gluon fragmentation mechanism which is related to multiple gluon emission in the initial state. The initial state emission is treated according to Catani-Ciafaloni-Fiorani-Marchesini evolution equation, and applies to both single and double parton scattering cases. We show the importance of fragmentation contributions to J/psi pair production and perform a comparison between theoretical predictions and the latest ATLAS data collected at root sp = 8 TeV. We find that the effects of multiple gluon emission are essential for both single- and multiparton interaction processes. Finally, we highlight the problem of correct choice of the factorization scale with respect to numerical stability of the calculations and the consistency with noncollinear evolution equations.