Transversity and Dihadron Fragmentation Functions *

The observation of the quark transversity distribution requires another soft object sensitive to the quark's transverse spin. Dihadron fragmentation functions represent a convenient tool to analyze partonic spin, which can influence the angular distribution of the two hadrons. In particular, the so-called interference fragmentation functions can be used to probe transversity both in semi-inclusive deep inelastic scattering as well as proton-proton collisions. We discuss two single-spin asymmetries sensitive to transversity in the these two processes, at leading twist and leading order in α S. Transversity has received a lot of attention during this conference. Its measurement is on the agenda of several experimental collaborations. However , it is still not clear what will turn out to be the best way to access it. Different options will be explored in the next few years: polarized Drell-Yan, polarized Λ production, azimuthal asymmetries in pion production and, finally, azimuthal asymmetries in two-pion production. a Each one of these processes has some advantages and drawbacks, making it necessary to explore all of them at the same time. Here, we focus on azimuthal asymmetries in two-hadron production. First of all we consider leptoproduction of two hadrons in the current fragmentation region, i.e. the process lp → l ′ (h 1 h 2)X. The outgoing hadrons have momenta P 1 and P 2 , masses M 1 and M 2 , and invariant mass * Work partially supported by the Alexander von Humboldt Foundation. a At the moment, data are available only for azimuthal asymmetries in pion production. 1