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

TL;DR

This study searches for a hypothetical light scalar particle produced in radiative Upsilon(3S) decays that could decay invisibly, setting upper limits on its production rate and constraining models predicting such particles.

Contribution

First experimental search for invisible decays of a light scalar in Upsilon(3S) radiative transitions, providing new upper limits on the process.

Findings

No evidence found for the decay process.

Set upper limits on branching fractions between 0.7 and 31 x 10^{-6}.

Constrained parameter space for models with light CP-odd Higgs bosons.

Abstract

We search for a light scalar particle produced in single-photon decays of the Upsilon(3S) resonance through the process Upsilon(3S) -> gamma A0, A0 -> invisible. Such an object appears in Next-to-Minimal Supersymmetric extensions of the Standard Model, where a light CP-odd Higgs boson naturally couples strongly to b-quarks. If, in addition, there exists a light, stable neutralino, decays of A0 could be preferentially to an invisible final state. We search for events with a single high-energy photon and a large missing mass, consistent with a 2-body decay of Upsilon(3S). We find no evidence for such processes in a sample of 122*10^6 Upsilon(3S) decays collected by the BABAR collaboration at the PEP-II B-factory, and set 90% C.L. upper limits on the branching fraction B(Upsilon(3S) -> gamma A0)*B(A0 -> invisible) at (0.7-31)*10^{-6} in the mass range m(A0)<=7.8 GeV. The results are preliminary.