A consistency test hiding in charm decay measurements

Charm quarks decaying into lighter particles should obey mathematical relations that link their lepton-flavor-universality ratios, analogous to well-studied sum rules in bottom decays. The team shows these charm sum rules are less precise but still constrain deviations to below one percent, making them useful consistency checks. They also predict the lepton-flavor ratio for the unmeasured $Λ_c → n$ decay.