Implications of a New Light Scalar Near the Bottomonium Regime

TL;DR

This paper investigates a light spin-0 particle near the bottomonium mass range, analyzing its decay modes into bottomonium states using NRQCD, and explores its potential experimental signatures in extended Higgs models.

Contribution

It provides the first detailed calculation of decay rates of a light scalar into bottomonium states in this mass range, including data-driven estimates for challenging cases.

Findings

Decay rates into bottomonium can surpass those into other fermions.

New experimental signatures include invisible decays to b-quarks.

Potential observability in extended Higgs sector decay chains.

Abstract

We study the decay modes of a new, light spin-0 particle, arguing that if the mass of the (pseudo)scalar is ~11-15 GeV, it can have an appreciable branching ratio into bottomonium, in particular the rare eta's. Using non-relativistic QCD (NRQCD), we calculate its decay rate to bottomonia for mass splittings greater than the typical momentum transfer within the bound state. It can exceed that of decays to other Standard Model fermions under the assumption of couplings proportional to those of the Standard Model. At smaller splittings, where our computational methods break down, we estimate the rate into bottomonia using data-driven methods. When the spin-0 state decays to bottomonia whose mass is too light to produce B-meson pairs, we get a qualitatively new experimental signature, decays to b-quarks invisible to b-tagging. Such a light, spinless particle can arise in extended Higgs sectors, making this channel potentially observable in decay chains initiated by the subdominant decay of a Standard Model-like Higgs to a pair of them.