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

Abstract

A study of the angular distributions of leptons from decays of J/psi's produced in p-C and p-W collisions at sqrt{s}=41.6 GeV has been performed in the Feynman-x region -0.34 < x_F < 0.14 and for transverse momentum 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 x 10^5 J/psi's reconstructed in both the e^+ e^- and mu^+ mu^- decay channels, indicate that J/psi's are produced with longitudinal polarization. The magnitude of the effect is maximal at low p_T. For p_T >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.

9 pages, 3 figures, 8 tables

References in corpus (5)

• Polarizations of J/psi and psi(2S) Mesons Produced in ppbar Collisions at 1.96 TeV
• Kinematic distributions and nuclear effects of $J/\psi$ production in 920 GeV fixed-target proton-nucleus collisions
• A Measurement of the Psi' to J/psi Production Ratio in 920 GeV Proton-Nucleus Interactions
• Production of the Charmonium States chic_1 and chic_2 in Proton Nucleus Interactions at sqrt{s} = 41.6 GeV
• J/Psi Polarization in 800-GeV p-Cu Interactions

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