Polarized Semi-Inclusive Deep-Inelastic Scattering at NNLO in QCD

Semi-inclusive hadron production in longitudinally polarized deep-inelasticlepton-nucleon scattering is a powerful tool for resolving the quark flavordecomposition of the proton's spin structure. We present the fullnext-to-next-to-leading order (NNLO) QCD corrections to the coefficientfunctions of polarized semi-inclusive deep-inelastic scattering (SIDIS) inanalytical form, enabling the use of SIDIS measurements in precision studies ofthe proton spin structure. The numerical impact of these corrections isillustrated by a comparison with data of polarized single-inclusive hadronspectra from the DESY HERMES and CERN COMPASS experiments.