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ABSTRACT: . Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the # 0 (770) meson over a range in the virtual photon negative four-momentum squared 0.5 < Q 2 < 4 GeV 2 and the photon-nucleon invariant mass range 3.8 < W < 6.5 GeV. The experiment was performed with the Hermes spectrometer, using a longitudinally polarized positron beam and a 3 He gas target internal to the HERA e storage ring. The event sample combines # 0 mesons produced incoherently o# individual nucleons and coherently o# the nucleus as a whole. The distributions in one production angle and two angles describing the # 0 # # + # - decay yielded measurements of eight elements of the spin-density matrix, including one that had not been measured before. The results are consistent with the dominance of helicity conserving amplitudes and natural parity exchange. The improved precision achieved at 4 < W < 7 GeV, in combination with other data at W > 7 GeV, re...