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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 π^{-} 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}. 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.

We studied simultaneously the 4 He(e, e p), 4 He(e, e pp), and 4 He(e, e pn) reactions at Q 2 = 2 (GeV/c) 2 and xB > 1, for an (e, e p) missing-momentum range of 400 to 830 MeV/c. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A = 2 system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum, in a region where the nucleon-nucleon (N N ) force is expected to change from predominantly tensor to repulsive. The abundance of neutron-proton pairs is reduced as the nucleon momentum increases beyond ∼500 MeV/c. The extracted fraction of proton-proton pairs is small and almost independent of the missing momentum. Our data are compared with calculations of two-nucleon momentum distributions in 4 He and discussed in the context of probing the elusive repulsive N N force.

We have performed the most comprehensive resonance-model fit of π − π − π þ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction π − þ p → π − π − π þ þ p recoil with a 190 GeV=c pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, 0.5 < m 3π < 2.5 GeV=c 2 , and simultaneously in 11 bins of the reduced four-momentum transfer squared, 0.1 < t 0 < 1.0 ðGeV=cÞ 2 , are subjected to a resonance-model fit using Breit-Wigner amplitudes to simultaneously describe a subset of 14 selected waves using 11 isovector light-meson states with J PC ¼ 0 −þ , 1 þþ , 2 þþ , 2 −þ , 4 þþ , and spin-exotic 1 −þ quantum numbers. The model contains the well-known resonances πð1800Þ, a 1 ð1260Þ, a 2 ð1320Þ, π 2 ð1670Þ, π 2 ð1880Þ, and a 4 ð2040Þ. In addition, it includes the disputed π 1 ð1600Þ, the excited states a 1 ð1640Þ, a 2 ð1700Þ, and π 2 ð2005Þ, as well as the resonancelike a 1 ð1420Þ. We measure the resonance parameters mass and width of these objects by combining the information from the PWA results obtained in the 11 t 0 bins. We extract the relative branching fractions of the ρð770Þπ and f 2 ð1270Þπ decays of a 2 ð1320Þ and a 4 ð2040Þ, where the former one is measured for the first time. In a novel approach, we extract the t 0 dependence of the intensity of the resonances and of their phases. The t 0 dependence of the intensities of most resonances differs distinctly from the t 0 dependence of the nonresonant components. For the first time, we determine the t 0 dependence of the phases of the production amplitudes and confirm that the production mechanism of the Pomeron exchange is common to all resonances. We have performed extensive systematic studies on the model dependence and correlations of the measured physical parameters.