Angular distributions of leptons from J/ψ’s produced in 920 GeV fixed-target proton-nucleus collisions
نویسندگان
چکیده
A study of the angular distributions of leptons from decays of J/ψ’s produced in p-C and p-W collisions at √ s = 41.6 GeV has been performed in the J/ψ Feynman-x region −0.34 < xF < 0.14 and for J/ψ transverse momenta up to 5.4 GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3 · 10 J/ψ’s reconstructed in both the ee and μμ decay channels, indicate that J/ψ’s are produced polarized. The magnitude of the effect is maximal at low pT . For pT > 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.
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