Search for Dimuon Decays of a Light Scalar Boson in Radiative Transitions Υ→γA0

Abstract

We search for evidence of a light scalar boson in the radiative decays of the Υ ( 2 S ) and Υ ( 3 S ) resonances: Υ ( 2 S , 3 S ) → γ A 0 , A 0 → μ + μ − . Such a particle appears in extensions of the standard model, where a light C P -odd Higgs boson naturally couples strongly to b quarks. We find no evidence for such processes in the mass range 0.212 ≤ m A 0 ≤ 9.3 GeV in the samples of 99 × 10 6 Υ ( 2 S ) and 122 × 10 6 Υ ( 3 S ) decays collected by the BABAR detector at the SLAC PEP-II B factory and set stringent upper limits on the effective coupling of the b quark to the A 0 . We also limit the dimuon branching fraction of the η b meson: B ( η b → μ + μ − ) < 0.9 % at 90% confidence level.