Spin effects in large angle two body reactions at high energy

Large angle two body processes at high energies are considered a most important class of reactions to test our understanding on the interaction of the hadronic constituents at short distances on the behaviour of hadronic from factors which contain basic information about the composite nature of hadrons.For massless quarks, the QCD vector interaction preserves the quark helicity an this strong spin constraint leads to the following selection rule for hadron helicities: λA+λB=λA′+λB′ for the reaction A+B→A′+B′.