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

Abstract

Abstract$$|\Delta c|=|\Delta u|=1$$ | Δ c | = | Δ 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 $$D \rightarrow \pi \ell \ell ^{(\prime )}$$ D → π ℓ ℓ ( ′ ) and $$D_s \rightarrow K \ell \ell ^{(\prime )}$$ D s → K ℓ ℓ ( ′ ) decays, $$\ell ^{(\prime )}=e, \mu $$ ℓ ( ′ ) = e , μ , and find large room for new physics safely above the SM contribution. We identify signatures of supersymmetry, leptoquarks and anomaly-free $$U(1)^\prime $$ U ( 1 ) ′ –models with generation-dependent charges, for which we provide explicit examples. $$Z^\prime $$ Z ′ –effects in $$c \rightarrow u \ell \ell ^{(\prime )}$$ c → u ℓ ℓ ( ′ ) transitions can be sizable if both left-handed and right-handed couplings to quarks are present.