Role of Collins effect in the single spin asymmetry A _N in p↑p→h X processes

The much debated issue of the transverse single spin asymmetry A _N observed in the inclusive large P _T production of a single hadron in pp interactions, p↑p→X, is considered in a transverse momentum dependent factorization scheme. A previous result stating that the maximum contribution of the Collins effect is strongly suppressed, is revisited, correcting a numerical error. New estimates are given, adopting the Collins functions recently extracted from semi-inclusive deep inelastic scattering and e ⁺e ^- data, and phenomenological consequences are discussed.