We compare results of the $k_t$-factorization approach and the next-to-leading-order collinear-factorization approach for dijet correlations in proton-proton collisions at RHIC energies. We discuss correlations in azimuthal angle as well as correlations in two-dimensional space of transverse momenta of two jets. Some $k_t$-factorization subprocesses are included for the first time in the literature. Different unintegrated gluon/parton distributions are used in the $k_t$-factorization approach. The results depend on unintegrated gluon distribution functions (UGDF)/unintegrated parton distribution function (UPDF) used. For the collinear next-to-leading order (NLO) case, the situation depends significantly on whether we consider correlations of any two jets or correlations of leading jets only. In the first case, the $2\to 2$ contributions associated with soft radiations summed up in the $k_t$-factorization approach dominate at $\varphi \sim \pi$ and at equal moduli of jet transverse momenta. The collinear NLO $2\to 3$ contributions dominate over $k_t$-factorization cross section at small relative azimuthal angles as well as for asymmetric transverse-momentum configurations. In the second case, the NLO contributions vanish at small relative azimuthal angles and/or large jet transverse-momentum disbalance due to simple kinematical constraints. There are no such limitations for the $k_t$-factorization approach. All this makes the two approaches rather complementary. The role of several cuts is discussed and quantified.

• Received 27 April 2007

DOI:https://doi.org/10.1103/PhysRevD.76.034001