Measurement of the mass and width of the D s 1 meson

The decay width and mass of the D s 1 ð 2536 Þ þ meson are measured via the decay channel D þ s 1 ! D (cid:1)þ K 0 S using 385 fb (cid:2) 1 of data recorded with the BABAR detector in the vicinity of the (cid:1) ð 4 S Þ resonance at the PEP-II asymmetric-energy electron-positron collider. The result for the decay width is (cid:2) ð D þ s 1 Þ ¼ 0 : 92 (cid:3) 0 : 03 ð stat : Þ (cid:3) 0 : 04 ð syst : Þ MeV . For the mass, a value of m ð D þ s 1 Þ ¼ 2535 : 08 (cid:3) 0 : 01 ð stat : Þ (cid:3) 0 : 15 ð syst : Þ MeV =c 2 is obtained. The mass difference between the D þ s 1 and the D (cid:1)þ is measured to be m ð D þ s 1 Þ (cid:2) m ð D (cid:1)þ Þ ¼ 524 : 83 (cid:3) 0 : 01 ð stat : Þ (cid:3) 0 : 04 ð syst : Þ MeV =c 2 , representing a significant improvement compared to the current world average. The unnatural spin-parity assignment for the D þ s 1 meson is confirmed.