Transverse spin effects in hadron-pair production from semi-inclusive   deep inelastic scattering
  First measurements of azimuthal asymmetries in hadron-pair production in deep-inelastic scattering of muons on transversely polarised ^6LiD (deuteron) and NH_3 (proton) targets are presented. The data were taken in the years 2002-2004 and 2007 with the COMPASS spectrometer using a muon beam of 160 GeV/c at the CERN SPS. The asymmetries provide access to the transversity distribution functions, without involving the Collins effect as in single hadron production. The sizeable asymmetries measured on the NH_ target indicate non-vanishing u-quark transversity and two-hadron interference fragmentation functions. The small asymmetries measured on the ^6LiD target can be interpreted as indication for a cancellation of u- and d-quark transversities. 
C. Adolph, M. G. Alekseev, V. Yu. Alexakhin, Yu. Alexandrov, G. D.   Alexeev, A. Amoroso, A. A. Antonov, A. Austregesilo, B....
hep-ex