Observation of a Narrow Charm-Strange Meson D_(sJ)~+(2632) → D_s~+ η and D~0K~+

摘要

We report the first observation of a charm-strange meson D_(sJ)~+(2632) at a mass of 2632.5 +-1.7 MeV/c~2 in data from SELEX, the charm hadro-production experiment E781 at Fermilab. This state is seen in two decay modes, D_s~+ η and D~0K~+. In the D_s~+ η decay mode we observe a peak with 101 events over a combinatoric background of 54.9 events at a mass of 2635.4 +- 3.3 MeV/c~2. There is a corresponding peak of 21 events over a background of 6.9 at 2631.5 +- 2.0 MeV/c~2 in the decay mode D~0K~+. The decay width of this state is <17 MeV/c~2 at 90% confidence level The relative branching ratio Γ(D~0K~+)/Γ(D_s~+ η) is 0.14 +- 0.06. The mechanism that keeps this state narrow is unclear. Its decay pattern is also unusual, being dominated by the D_s~+ η decay mode.