Flavor violating Higgs and $Z$ decays at FCC-ee

TL;DR

This paper evaluates FCC-ee's potential to detect flavor-violating Higgs and Z decays to quarks, updating Standard Model predictions and exploring implications for beyond Standard Model physics like two Higgs doublets and vectorlike quarks.

Contribution

It provides a detailed assessment of FCC-ee's sensitivity to rare flavor-violating decays and explores new physics parameter space beyond existing constraints.

Findings

FCC-ee can set relevant bounds on $Z/h o bs, cu$ decays.

Updated SM predictions for these branching ratios.

Probing new physics models with flavor-violating decays at FCC-ee.

Abstract

Recent advances in $b$, $c$, and $s$ quark tagging coupled with novel statistical analysis techniques will allow future high energy and high statistics electron-positron colliders, such as the FCC-ee, to place phenomenologically relevant bounds on flavor violating Higgs and $Z$ decays to quarks. We assess the FCC-ee reach for $Z/h\to bs, cu$ decays as a function of jet tagging performance. We also update the SM predictions for the corresponding branching ratios, as well as the indirect constraints on the flavor violating Higgs and $Z$ couplings to quarks. Using type III two Higgs doublet model as an example of beyond the standard model physics, we show that the searches for $h\to bs, cu$ decays at FCC-ee can probe new parameter space not excluded by indirect searches. We also reinterpret the FCC-ee reach for $Z\to bs , cu$ in terms of the constraints on models with vectorlike quarks.