Phenomenology of single spin asymmetries in p up arrow p ->pi X - art. no.054027

A phenomenological description of single transverse spin effects in hadron- hadron inclusive processes is proposed, assuming a generalized factorizatio n scheme and PQCD hard interactions. The transverse momentum k(perpendicula r to) of the quarks inside the hadrons and of the hadrons relative to the f ragmenting quark is taken into account in distribution and fragmentation fu nctions, and leads to possible nonzero single spin asymmetries. The role of k(perpendicular to) and spin-dependent quark fragmentations-the so-called Collins effect-is investigated in details in p (1)p --> pi X processes: it is shown how the experimental data could be described, obtaining an explici t expression for the spin asymmetry of a polarized fragmenting quark, on wh ich some comments are made. Predictions for other processes, possible furth er applications, and experimental tests are discussed. [S0556-2821(99)06415 -2].