  A single-spin asymmetry was measured in the azimuthal distribution of pi+pi-
pairs produced in semi-inclusive deep-inelastic scattering on a transversely
polarized hydrogen target. For the first time, evidence is found for a
correlation between the transverse target polarization and the azimuthal
orientation of the plane containing the two pions.The corresponding single-spin
asymmetry is expected to be related to the product of the little-known quark
transversity distribution function and an unknown naive-T-odd chiral-odd
dihadron fragmentation function.
