Speaker
Description
The first measurement of transverse-spin-dependent azimuthal
asymmetries in the pion-induced Drell-Yan (DY) process will be
presented, which was reported in PRL 119, 112002. 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/c2 and 8.5 GeV/c2. Within the experimental uncertainties,
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. A recent COMPASS SIDIS measurement was
obtained at a hard scale comparable to that of these DY results. This
opens the way for possible tests of fundamental QCD universality
predictions.
