Observation of the decay

Using the ARGUS detector at the e + e - storage ring using DORIS II at DESY, we have observed a new decay channel for the excited charm-strange meson D s1 (2536) + →D∗ O K + . The production cross section for the D s 1 (2536) + decaying via this channel is measured to be σ ( D s1 (2536) + )· BR (D sl (2536) + →D∗ 0 K + )= 18±4±3 pb at E CM = 10.4 GeV. The mass of the D s 1 (2536) + is found to be 2535.2 ± 0.5±1.5 MeV/ c 2 in agreement with the value obtained from an analysis of the D s1 (2536) + →D∗ + K 0 s decay channel. The natural width is determined to be less than 3.9 MeV/ c 2 at 90%CL.