  Recently HERMES has observed an azimuthal asymmetry in electro-production of
neutral pions in semi-inclusive deep-inelastic scattering of unpolarized
positrons off longitudinally polarized protons. This asymmetry (like those
observed in the production of charged pions) is well reproduced theoretically
by using the non-perturbative calculation of the proton transversity
distribution in the effective chiral quark-soliton model combined with
experimental DELPHI-data on the new T-odd Collins fragmentation function. There
are no free, adjustable parameters in the analysis. Using the $z$-dependence of
the HERMES azimuthal asymmetry and the calculated transversity distributions
the z-dependence of the Collins fragmentation function is obtained. The value
obtained from HERMES data is consistent with the DELPHI result, even though
these results refer to different scales.
