AbstractWe consider the prompt double $$J/\psi $$
J
/
ψ
production in pp collisions at the LHC in the framework of $$k_T$$
k
T
-factorization QCD approach. Using the fragmentation mechanism, we evaluate the color octet contributions to the production cross sections taking into account the combinatorial effects of multiple gluon radiation in the initial state driven by the Ciafaloni–Catani–Fiorani–Marchesini evolution equation. We demonstrate the importance of these contributions in a certain kinematical region covered by the CMS and ATLAS measurements. On the other hand, the experimental data taken by the LHCb Collaboration at forward rapidities and moderate transverse momenta can be described well by $${{{\mathcal {O}}}}(\alpha _s^4)$$
O
(
α
s
4
)
color singlet terms and contributions from the double parton scattering mechanism. The extracted value of the effective cross section is compatible with many other estimations based on different final states.
Double-parton scattering mechanism for associated
cc¯l+l−
production in
AA
ultraperipheral collisions as a probe for the photon density inside the nucleus