The future COMPASS-II Drell–Yan program

Much of the information that exists today on Transverse Momentum Dependent Parton Distribution Functions (TMDs) comes from SIDIS measurements with unpolarised and polarised beams and targets where they appear convoluted with fragmentation functions (FFs). Drell–Yan (DY) measurements are complementary to those by SIDIS experiments, as they allow to measure convolutions of only Parton Distribution Functions (PDFs) without involving FFs. Moreover, given the T-odd character of both Sivers and Boer-Mulders functions, the sign of these TMDs is expected to be reversed when observed from SIDIS or from DY. Measurements of SIDIS were performed by COMPASS in the period 2002 to 2007 and in 2010, using a naturally polarised μ+ beam and a solid state target polarised either longitudinally or transversely with respect to the beam direction. Now the COMPASS-II Experiment will have the unique opportunity to access TMDs from single-polarised Drell–Yan processes as well, allowing to test the sign change prediction for the first time. We present here the future polarised DY measurements at COMPASS-II, which are foreseen to start in late 2014.