Constraining the parameter space of a singlet down-type vector-like quark

Abstract

We consider a minimal New Physics scenario in which the Standard Model is extended by singlet down-type vector-like quark(VLQ). We constrain its parameter space using the measured branching ratios for $B_s \to μ^+ μ^-$, $B \to X_s μ^+ μ^-$ and $B \to X_s γ$, which are all consistent with Standard Model predictions. Besides considering the tree-level flavor-changing-neutral-current amplitude allowed in this NP scenario, we account for a Higgs--VLQ loop amplitude and show that their resulting interference drives the VLQ mass into the discovery reach via direct searches at the LHC. We also examine the implications of this minimal NP scenario for the rare $B \to K ν\barν$ decay where there is a persistent tension between the SM prediction and the Belle II measurements.