Quark flavour-violating Higgs decays at the ILC

TL;DR

This paper explores the potential to detect rare quark flavour-violating Higgs decays at the ILC, focusing on the decay to a bottom and a light quark, and assesses the experimental sensitivity and background challenges.

Contribution

It provides a detailed analysis of the ILC's sensitivity to Higgs flavour-violating decays, highlighting the importance of flavour tagging and identifying promising detection channels.

Findings

Expected 95% CL upper limit on branching ratio: ~10^{-3}

Discovery potential for branching ratios as low as a few 10^{-3}

Identifies the two-jet plus missing energy channel as most promising

Abstract

Flavour-violating Higgs interactions are suppressed in the Standard Model such that their observation would be a clear sign of new physics. We investigate the prospects for detecting quark flavour-violating Higgs decays in the clean ILC environment. Concentrating on the decay to a bottom and a light quark $j$, we identify the dominant Standard Model background channels as coming from hadronic Standard Model Higgs decays with mis-identified jets. Therefore, good flavour tagging capabilities are essential to keep the background rate under control. Through a simple cut-based analysis, we find that the most promising search channel is the two-jet plus missing energy signature $e^+e^-\to bj+E_{T}^\text{miss}$. At 500 GeV, the expected $95\,$% CL upper limit on $\mathcal{B}(h\to bj)$ is of order $10^{-3}$. Correspondingly, a $5\,\sigma$ discovery is expected to be possible for branching ratios as low as a few $10^{-3}$.