Associated production of pairs with a gluon in the collinear-factorization approach
Izabela Babiarz (Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, PL-31-342 Kraków, Poland); Wolfgang Schäfer (Institute of Nuclear Physics, Polish Academy of Sciences, ul. Radzikowskiego 152, PL-31-342 Kraków, Poland); Antoni Szczurek (Faculty of Mathematics and Natural Sciences, University of Rzeszów, ul. Pigonia 1, PL-35-310 Rzeszów, Poland)
We calculate cross section for production of pairs in proton-proton collisions. The cross section for the is considerably smaller (especially for the final state) than that obtained recently in the -factorization approach. We calculate therefore next-to-leading order (NLO) contributions with the pair and one extra associated (mini-)jet. We find these contributions to be much larger than those for the contribution. Especially the emission of a leading gluon (carrying a large momentum fraction of one of the incoming gluons) is important. These emissions in the -factorization approach are absorbed into the initial state unintegrated gluon distributions. A smaller contribution to the cross section comes from the production of central gluons emitted with rapidities between the mesons. They do lead, however, to an enhancement of the -pair production at large rapidity distance between the mesons. Our present study explains the size of the cross section for the -pair production obtained previously in the -factorization approach. Several differential distributions are presented.