Hidden resonances reshape the search for new physics in rare B decays

B mesons decaying to kaons and tau leptons are cluttered with intermediate resonances (like ψ(2S)) that distort the signal across the energy spectrum. The authors included these resonances directly in their predictions rather than trying to cut them out, using LHCb muon decay data to constrain the effect. The result: resonances boost Standard Model rates by substantial factors, but also create room for large new physics contributions to hide—or stand out more clearly—depending on the energy region examined.