Large apparent $SU(3)_F$ breaking and a tension with lattice QCD have recently emerged in semileptonic decays of singly charmed baryons, hinting at either an unexpected hadronic mechanism or new physics. We formulate a framework that systematically matches lattice-QCD inputs onto an $SU(3)_F$ analysis including first-order symmetry breaking. We predict ${ \mathcal{ B}}(\Xi_c^+\to\Sigma^0\ell^+\nu_\ell)/{ \mathcal{ B}}(\Xi_c^+\to\Xi^0\ell^+\nu_\ell)=(2.6\pm0.3)\%,$ and ${ \mathcal{ B}}(\Xi_c^+\to\Lambda^0\ell^+ \nu_\ell)/{ \mathcal{ B}}(\Xi_c^+\to\Xi^0\ell^+\nu_\ell)=(1.1\pm0.1)\%$, whose precise measurements would cleanly determine the origin of the anomalously large $SU(3)_F$ breaking.
Categories: hep-ph hep-ex hep-lat