Polarized Fragmentation Functions

play a similarly fundamental role as those of the corresponding crossed ‘spacelike’ deep-inelastic scattering (DIS) process ep → eX . Their interpretation in terms of scale-dependent fragmentation functions D f (z,Q ), the ‘time-like’ counterparts of the parton distribution functions fH(x,Q ) of a hadron H , hence provides a further important, complementary test of perturbative QCD. Furthermore, in the polarized case, they provide information about how the spin carried by the partons is passed to the hadrons in the fragmentation process and, at variance with DIS, it is possible to measure them even for the case of hadrons which are not available as targets. Among all the hadrons, the production of Λ baryons appears to be particularly interesting: the self-analyzing properties of its dominant weak decay Λ → pπ and the particularly large asymmetry of the angular distribution of the decay proton in the Λ rest-frame allow for an experimental reconstruction of the Λ spin. In the following we will address the issue of fragmentation into polarized Λ’s within a detailed QCD analysis. We will provide some realistic sets of unpolarized and polarized fragmentation functions for Λ baryons. Since there are hardly any data sensitive to the polarized fragmentation functions ∆D f , one has to rely on reasonable assumptions. Our various proposed sets for ∆D f , which are all compatible with the LEP data, are particularly suited for estimating the physics potential of different