H + Probes: b → s ϒ , and B → τ ν , D (✼) τ ν

When the observation of \(b\rightarrow s\gamma \) was first announced by CLEO [1] in 1994 with 2 fb\(^{-1}\) data on the \(\varUpsilon (4S)\), it immediately became one of the most powerful constraints on many kinds of New Physics that enter the loop. In this Chapter, we illustrate by the stringent bound it provides on the charged Higgs boson \(H^+\) that automatically exists in minimal SUSY. A second probe of the \(H^+\) boson is, surprisingly a tree level effect in \(B^+\rightarrow \tau ^+\nu \), which became relevant only when full-reconstruction tag (of the other B) method matured at the B factories. This in turn led finally to the measurement of the \(B \rightarrow D^{(*)}\tau \nu \) modes, which are tree level processes with large decay rates, and turned surprisingly into a leading “anomaly” in the LHC era.