ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2010, vol. 105, p. -
Search for a low mass particle decaying into μ+μ - in B0→K*0X and B0→ρ0X at Belle
We search for dimuon decays of a low mass particle in the decays B0→K*0X and B0→ρ0X using a data sample of 657×106BB̄ events collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find no evidence for such a particle in the mass range from 212MeV/c2 to 300MeV/c2 for lifetimes below 10-12s, and set upper limits on its branching fractions. In particular, we search for a particle with a mass of 214.3MeV/c2 reported by the HyperCP experiment, and obtain upper limits on the products B(B0→K *0X)×B(X→μ+μ-)<2. 26(2.27)×10-8 and B(B0→ρ0X) ×B(X→μ+μ-)<1.73(1.73)×10 -8 at 90% C.L. for a scalar (vector) X particle. © 2010 The American Physical Society.