Lambda asymmetries

The measurement of the transverse spin quark distribution functions $\Delta_{T}q(x)$ is an important part of the physics program of the COMPASS experiment at CERN. The transversity distributions, being chiral-odd objects, are not accessible in inclusive deep inelastic scattering (DIS). The most promising channels for the measurement of the transversity distributions in semi-inclusive DIS (SIDIS) are the Collins effect, the azimuthal asymmetries in two hadrons production and the spin transfer to the Lambda hyperons. In this paper we focus on the semi-inclusive Lambda production mechanism, showing the connection between the measured polarization and the $\Delta_{T}q(x)$ functions. We derive an expression for the experimental $\Lambda\rightarrow p\pi^{-}$ angular distribution that is at first order independent of the experimental acceptance, and we present the preliminary results for the Lambda polarization as a function of the $x$ Bjorken variable. The analysis is based on the 2002 and 2003 COMPASS data with transverse spin target configuration.