  The HERMES experiment has measured for the first time single target-spin
asymmetries in semi-inclusive two-pion production using a transversely
polarized hydrogen target. These asymmetries are related to the product of two
unknowns, the transversity distribution function and the interference
fragmentation function. In the invariant mass range 0.51 GeV < M_inv < 0.97 GeV
the measured asymmetry deviates significantly from zero, indicating that
two-pion semi-inclusive deep-inelastic scattering can be used to probe
transversity.
