Angular distributions of leptons from J/ψ’s produced in 920 GeV fixed-target proton-nucleus collisions

A study of the angular distributions of leptons from decays of J/ψ’s produced in p-C and p-W collisions at \(\sqrt{s}=41.6\mbox{~GeV}\) has been performed in the J/ψ Feynman-x region −0.34 1 GeV/c a significant dependence on the reference frame is found: the polar anisotropy is more pronounced in the Collins-Soper frame and almost vanishes in the helicity frame, where, instead, a significant azimuthal anisotropy arises.