Study of the X(3872) and Y(4260) in B0→J/ψπ+π-K0 and B-→J/ψπ+π-K- decays

We present results of a search for the X(3872) in B0→X(3872)KS0, X(3872)→J/ψπ+π-, improved measurements of B-→X(3872)K-, and a study of the J/ψπ+π- mass region above the X(3872). We use 232×106 BB pairs collected at the Υ(4S) resonance with the BABAR detector at the PEP-II e+e- asymmetric-energy storage rings. The results include the 90% confidence interval 1.34×10-6X(3872)K0, X→J/ψπ+π-)<10.3×10-6 and the branching fraction B(B-→X(3872)K-,X→J/ψπ+π-)=(10.1±2.5±1.0) ×10-6. We observe a (2.7±1.3±0.2)MeV/c2 mass difference of the X(3872) produced in the two decay modes. Furthermore, we search for the Y(4260) in B decays and set the 95% C.L. upper limit B(B-→Y(4260)K-,Y(4260) →J/ψπ+π-)<2.9×10-5. © 2006 The American Physical Society.