Search for Dimuon Decays of a Light Scalar in Radiative Transitions Y(3S) -> gamma A0

TL;DR

This study searches for a light scalar particle in radiative Y(3S) decays to dimuons, setting upper limits on its production and decay rates, and also constrains the eta_b meson’s dimuon decay probability.

Contribution

It provides the first experimental upper limits on the product of branching fractions for a light scalar in Y(3S) decays and on the eta_b dimuon decay, within a broad mass range.

Findings

No evidence for the light scalar in the specified mass range.

Set upper limits on the product of branching fractions from 0.25 to 5.2 x 10^{-6}.

Constrained the eta_b meson’s dimuon decay branching fraction to less than 0.8%.

Abstract

The fundamental nature of mass is one of the greatest mysteries in physics. The Higgs mechanism is a theoretically appealing way to account for the different masses of elementary particles and implies the existence of a new, yet unseen particle, the Higgs boson. We search for evidence of a light scalar (e.g. a Higgs boson) in the radiative decays of the narrow Y(3S) resonance: Y(3S)->gamma A0, A0->mu+mu-. Such an object 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 a sample of 122*10^6 Y(3S) decays collected by the BABAR collaboration at the PEP-II B-factory, and set 90% C.L. upper limits on the branching fraction product B(Y(3S)-> gamma A0)*B(A0->mu+mu-) at (0.25-5.2)*10^{-6} in the mass range 0.212<= m(A0)<=9.3 GeV. We also set a limit on the dimuon branching fraction of the eta_b meson B(eta_b->mu+mu-)<0.8% at 90% C.L. The results are preliminary.