Search for Dimuon Decays of a Light Scalar Boson in Radiative Transitions Upsilon -> gamma A0

TL;DR

This study searches for a light scalar boson in radiative Upsilon decays to muon pairs, finding no evidence but setting upper limits on its coupling and the eta_b meson's dimuon decay rate.

Contribution

First search for a light scalar boson in Upsilon radiative decays with stringent upper limits on coupling and branching fractions.

Findings

No evidence for the scalar boson in the mass range 0.212-9.3 GeV.

Set upper limits on the b-quark coupling to A0.

Limit on eta_b -> mu+ mu- branching fraction to less than 0.9%.

Abstract

We search for evidence of a light scalar boson in the radiative decays of the Upsilon(2S) and Upsilon(3S) resonances: Upsilon(2S,3S)-> gamma A0, A0 -> mu^+ mu^-. Such a particle appears in extensions of the Standard Model, where a light CP-odd Higgs boson naturally couples strongly to b-quarks. We find no evidence for such processes in the mass range 0.212<= m(A0)<= 9.3 GeV in the samples of 99*10^6 Upsilon(2S) and 122*10^6 Upsilon(3S) decays collected by the BABAR detector at the PEP-II B-factory and set stringent upper limits on the effective coupling of the b quark to the A0. We also limit the dimuon branching fraction of the eta_b meson: BR(eta_b->mu^+mu^-)<0.9% at 90% confidence level.