The new physics reach of null tests with D rightarrow pi ell ell and D_s rightarrow K ell ell decays

Abstract

|Delta c|=|Delta u|=1 processes are unique probes of flavor physics in the up-sector within and beyond the Standard Model (SM). SM tests with rare semileptonic charm meson decays are based on an approximate CP–symmetry, a superior GIM–mechanism, angular distributions, lepton-universality and lepton flavor conservation. We analyze the complete set of null test observables in D rightarrow pi ell ell ^{(prime )} and D_s rightarrow K ell ell ^{(prime )} decays, ell ^{(prime )}=e, mu , and find large room for new physics safely above the SM contribution. We identify signatures of supersymmetry, leptoquarks and anomaly-free U(1)^prime –models with generation-dependent charges, for which we provide explicit examples. Z^prime –effects in c rightarrow u ell ell ^{(prime )} transitions can be sizable if both left-handed and right-handed couplings to quarks are present.