Single hadron multiplicities in SIDIS at COMPASS

Single hadron fragmentation functions, FFs, play an important role in several aspects of hadronic spin physics. In particular, they are crucial for the determination of flavour separated polarized parton distribution functions (polarized PDFs) from Semi-Inclusive DIS data.The COMPASS collaboration at CERN is undertaking a programme of measurements of pion and kaon multiplicities in SIDIS for the purpose of extracting these FFs. Preliminary results, derived from muon-nucleon scattering data collected on an LiD target, are presented. The dependence of the multiplicities upon transverse momentum, $p_{T}$ , is also investigated, having in view, this time, the dependence of the PDFs and FFs upon the parton intrinsic motion. Preliminary findings, obtained for unidentified charged hadrons, are reported.