We discuss the production of transversely polarized hyperons in unpolarized proton-proton collisions in the framework of the collinear twist-3 factorization.
We focus on the contribution from the twist-3 fragmentation functions for the final hyperon, that represent the effect of multi-parton correlations in the fragmentation process. This contribution consists of the quark fragmentation one and the gluon fragmentation one. We present the twist-3 cross section for the former in the Leading Order (LO) with respect to the QCD coupling constant.
We also present a new formalism to calculate the cross section for the latter contribution. These contributions are as important as that from the twist-3 distribution in the initial proton combined with the transversity fragmentation function for the final hyperon.