The first measurement of transverse-spin-dependent azimuthal asymmetries in
the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190
GeV/$c$, $pi^{-}$ beam and a transversely polarized ammonia target. Three
azimuthal asymmetries giving access to different transverse-momentum-dependent
(TMD) parton distribution functions (PDFs) are extracted using dimuon events
with invariant mass between 4.3 GeV/$c^2$ and 8.5 GeV/$c^2$. The observed sign
of the Sivers asymmetry is found to be consistent with the fundamental
prediction of Quantum Chromodynamics (QCD) that the Sivers TMD PDFs extracted
from DY have a sign opposite to the one extracted from semi-inclusive
deep-inelastic scattering (SIDIS) data. We present two other asymmetries
originating from the pion Boer-Mulders TMD PDFs convoluted with either the
nucleon transversity or pretzelosity TMD PDFs. These DY results are obtained at
a hard scale comparable to that of a recent COMPASS SIDIS measurement and hence
allow unique tests of fundamental QCD universality predictions.
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