Preliminary measurements of transversity at COMPASS

COMPASS is a new fixed target experiment presently running at CERN. Using a 160 GeV polarised muon beam coming from the SPS and scattered off a $^{6}$LiD polarised target, the spin structure of the nucleon is determined from polarised semi-inclusive DIS (p-SIDIS) reactions. In particular the $h_{1}$ structure function can be measured via the so-called Collins effect. In 2002 we collected SIDIS data in transverse spin configuration for a total integrated luminosity of about 1.9 $\times$ 10$^{38}$cm$^{2}$. The expected statistical error coming from these data has been compared with existing QCD-based phenomenological calculations.