The COMPASS experiment at CERN is one of the leading experiments studying the spin structure of the nucleon. Until now, the Parton Distribution Functions (PDFs) and the Transverse Momentum... Show moreThe COMPASS experiment at CERN is one of the leading experiments studying the spin structure of the nucleon. Until now, the Parton Distribution Functions (PDFs) and the Transverse Momentum Dependent Parton Distribution Functions (TMD PDFs) of protons and deuterons have been studied in Semi-Inclusive Deep Inelastic Scattering (SIDIS) measurements. The polarised Drell-Yan (DY) process is a complementary way to access the TMD PDFs, as it allows us to measure convolutions of only PDFs without involving fragmentation functions (FFs). COMPASS aims to perform the first ever polarised DY experiment in the world, which is foreseen to start in late 2014. By detecting dimuons from DY events we will be able to extract azimuthal spin asymmetries, each containing a convolution of two TMD PDFs, one from a negative pion beam with a momentum of 190 GeV/c and the other one from a transversely polarised proton target (NH₃). After their disentangling we can access four of the eight TMD PDFs needed to describe the nucleon structure at leading twist, like the Sivers and the Boer-Mulders functions. The opportunity to study, in the same experiment, the TMD PDFs from both SIDIS and DY processes is unique at COMPASS. Therefore, we are in privileged conditions to confirm or to deny the expected sign change in Sivers and Boer-Mulders functions when accessed via DY or SIDIS processes. An overview of the preparation and future measurements of the polarised DY experiment will be provided. Show less
