Overview of the COMPASS Experimental Programme on TMDs and GPDs

The investigation of the recently introduced transverse momentum dependent (TMD) parton distribution functions (PDFs) and generalized parton distributions (GPDs) is an important part of the programme of the COMPASS experiment at CERN. A variety of Semi-inclusive deeply inelastic scattering (SIDIS) measurements on transversely polarized proton and deuteron targets from the 2002–2010 data have allowed to obtain a wealth of results on the transversity distribution and on the TMD PDFs. Further SIDIS measurements are planned in 2016 and 2017 on a pure hydrogen target. In a complementary approach, the first ever Drell–Yan measurement on a transversely polarized proton target is the objective of the 2015 run, still ongoing at the time of this conference, to address the fundamental issue of the change of sign of the Sivers function when measured in the Drell–Yan process as compared to that measured in SIDIS. GPDs are also being investigated. Measurements of the exclusive muon-production of vector mesons, in particular the $\rho ^0$ and the $\omega $ , on transversely polarized proton targets have provided information on the GPD E. Preliminary results from a test run on deeply virtual compton scattering of 160 GeV muons on a liquid hydrogen target are also given, as well as plans for a two-year long run in 2016 and 2017 with a suitably modified spectrometer.