Double inclusive cross-sections for gluon production in collision of two   projectiles on two targets in the BFKL approach
  Double inclusive cross-sections for gluon production in collision of two nucleons with two nucleons are studied in the BFKL approach. Various contributions include emission from the pomerons attached to the participants, from the BFKL interactions between these pomerons and from the intermediate BKP state. The last contribution may be observable provided the growth with energy of the pomeron contribution is tamed in accordance with unitarity. Possibility of long-range azimuthal correlations due to the BKP state are discussed. 
M.A.Braun
hep-ph