Single transverse spin asymmetry for large-pT pion production in semi-inclusive deep inelastic scattering

We study the single spin asymmetry (SSA) for the pion production with large transverse momentum PT in semi-inclusive deep inelastic scattering ep up arrow -> e pi X. We derive the twist-3 cross section formula for SSA, focussing on the soft-gluon-pole contributions associated with the twist-3 distribution for the nucleon and with the twist-3 fragmentation function for the pion. We present a simple estimate of the asymmetries due to each twist-3 effect from nucleon and pion, respectively, by fixing the overall strength of the relevant nonperturbative quantities by the data on the SSA A(N) in p up arrow p -> pi X collision. (c) 2006 Elsevier B.V. All rights reserved.