Bottom-Quark Contributions to Composite Pseudo-Scalar Couplings at Lhc

Composite Higgs models which describe the Higgs boson as a bound state emerging as pseudo-NambuGoldstone boson (pNGB) of a broken global symmetry are expected to be accompanied by additional resonances, some of which will occur ubiquitously. The subject of this work, a light pseudo-scalar which is the pNGB of a broken U(1) symmetry, is one such state, and may provide evidence of a composite Higgs model, should it be detected. We study the phenomenology of the scalar, examining its production and decay, with particular emphasis on its interaction with gauge bosons, which proceed via triangle diagrams in which run Standard Model quarks. Previously, only the top quark has been considered to contribute; however, we show that, particularly for low mass of the scalar, the bottom quark loop in fact provides a dominant contribution to the production cross section and modifies decay modes in a manner which should not be neglected. If targeted low mass searches for such a resonance are to be performed, it is crucial that the associated phenomenology be accurately modelled, in both the analysis of existing LHC data and for future high energy analyses.