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

We study the single spin asymmetry (SSA) for the pion production with large transverse momentum pTpT in semi-inclusive deep inelastic scattering ep↑→eπXep↑→eπX. 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 ANAN in p↑p→πXp↑p→πX collision.