Measurement of Azimuthal Asymmetries in Inclusive Production of Hadron Pairs in e+e- Annihilation at Belle

The so-called Collins fragmentation function connects the transverse quark spin with a measurable azimuthal dependence of the produced hadrons around the quark's momentum axis. Therefore, it can be used as a transverse spin analyzer in semi-inclusive deep inelastic scattering (DIS) and proton-proton collisions. While in those measurements the Collins function appears convolved with the so far unknown quark transversity distribution, it is directly accessible in e+e- collisions, where one measures a combination of a quark and an anti-quark fragmentation function. Using two different reconstruction methods we observe statistically significant azimuthal asymmetries of (3.26+-0.56+-0.55)% and (4.44+-0.67+-0.68)% for charged pion pairs in $e^+e^-$ annihilation at a center of mass energy of 10.52 GeV, which can be attributed to a transverse polarization of the primordial quarks.