Recent COMPASS results on Transverse Spin Asymmetries in SIDIS

Abstract

After reviewing the most important COMPASS results on transverse spin effects in SIDIS, I will present the recent work we have done on weighted Sivers asymmetries and "transversity induced" $\Lambda$ polarisation. Using the high statistics data collected in 2010 on a transversely polarised proton target COMPASS has evaluated the transverse momentum weighted Sivers asymmetries both in $x$- and in $z$-bins. The results are also compared with the standard unweighted asymmetries. Using the whole data sample collected over the years on transversely polarised deuteron and proton targets COMPASS has measured the transversity induced $\Lambda$ polarisation in the reaction $\mu N \rightarrow \mu' \Lambda X$. Possible future SIDIS COMPASS measurements will also be briefly mentioned.