The role of semi inclusive DIS data in determining polarized PDFs

A new combined NLO QCD analysis of the polarized inclusive and semi-inclusive DIS data is presented. In contrast to previous combined analyses, the 1/Q2 terms (kinematic –target mass corrections, and dynamic – higher twist corrections) in the expression for the nucleon spin structure function g1 are taken into account. The new COMPASS data are included in the analysis. The impact of the semi-inclusive (SIDIS) data on the polarized parton densities (PDFs) and on the higher twist corrections is demonstrated. The incompatibility of the polarized strange quark density obtained from DIS and from SIDIS data is discussed.