The polarised Drell-Yan measurement in COMPASS at CERN

 In 2015, COMPASS at CERN measured so-called “polarized Drell-Yan (DY)” process: π^- + p -> μ⁺+μ^-+X, where spin of p is polarized. Azimuthal asymmetries of μ⁺μ^- pairs (dimuons) as results of collisions of a π^- beam with momentum of 190 GeV/c and transversely polarized proton target enable us to access transverse momentum dependent parton distribution functions (TMD-PDFs) of a pion and a proton. Sivers function, which is one of TMD-PDFs, describes a correlation between a transverse spin of the nucleon and an intrinsic transverse momentum of a parton. If a value of the function is not zero, it suggests the existence of the orbital angular momentum of a parton. To extract TMD-PDFs, the asymmetries need to be treated as convolutions of the PDFs of a pion and a proton. COMPASS published the first results of the asymmetries in 2017. If the asymmetries are weighted with a transverse momentum of the dimuon (q_T), they can be understood as simple products of PDFs. Therefore the q_T-weighted method is fascinating tool to obtain TMD-PDFs more straightforwardly. In 2018, we measure the polarized DY process again to have more event statistics.

 In this talk, the recent status of the data taking in 2018 and results of asymmetry analysis will be presented.