The contribution of the four-parton final states to γ*γ*→ hadrons

In the analysis of the total cross section for the gamma* gamma* -> hadronsprocess, we include the four parton final states, which are part of theO(alpha_s^2) corrections. The four-parton final states contain the diagramswith gluon exchange in the crossed channel, which constitute the leading orderof the BFKL resummation. We show that the diagrams with gluon exchange in thecrossed channel play an important role in the large Y region, however theircontribution to the cross section must be evaluated exactly. In fact, thehigh-energy limit, which constitutes the kinematic framework of the BFKLresummation, is not sufficiently accurate at LEP2 energies. The inclusion ofthe diagrams with gluon exchange in the crossed channel reduces the discrepancybetween the theory and the LEP2 data collected by the L3 Collaboration, but thedata still lie above the theory, even allowing for a large scale uncertainty inthe theory. Thus, in order to describe accurately the data for gamma* gamma* ->hadrons in the large Y region, corrections of an order higher than O(alpha_s^2)seem to be necessary.Comment: 32 pages, 10 figures, published versio