Search for a Low Mass Particle Decaying into mu^+ mu^- in B0-> K*0 X and B0-> rho0 X at Belle

TL;DR

This study searches for a low mass particle decaying into muons in B0 meson decays using Belle data, finds no evidence, and sets upper limits on its possible branching fractions in the specified mass range.

Contribution

First search for a low mass dimuon particle in B0 decays with Belle data, providing new upper limits on its branching fractions.

Findings

No evidence for the particle in the mass range 212-300 MeV/c2.

Upper limits on branching fractions are set at 90% confidence level.

Specific limits for a 214.3 MeV/c2 particle reported by HyperCP.

Abstract

We search for dimuon decays of a low mass particle in the decays B0->K*0 X and B0->rho X using a data sample of 657x10^6 B Bbar 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 212 MeV/c2 to 300 MeV/c2, and set upper limits on its branching fractions. In particular, we search for a particle with a mass of 214.3 MeV/c2 reported by the HyperCP experiment, and obtain upper limits on the products B(B0->K*0 X)xB(X->mu^+ mu^-) < 2.26 (2.27)x10^-8 and B(B0->rho0 X)xB(X->mu^+ mu^-) < 1.73 (1.73)x10^-8 at 90% C.L. for a scalar (vector) X particle.