$\Xi_c \to \Xi$ form factors from lattice QCD with domain-wall quarks: A new piece in the puzzle of $\Xi_c^0$ decay rates

Abstract

We present a lattice-QCD determination of the vector and axial-vector form factors that describe the charm-baryon semileptonic decays $\Xi_c\to \Xi \ell^+ \nu_\ell$. The calculation uses a domain-wall action for the up, down, and strange quarks, and an anisotropic clover action for the charm quark. We use four ensembles of gauge-field configurations generated by the RBC and UKQCD collaborations, with lattice spacings between 0.111 and 0.073 fm and pion masses ranging from 420 to 230 MeV. We present Standard-Model predictions for the decay rates and branching fractions of $\Xi_c^0\to \Xi_c^-\ell^+ \nu_\ell$ and $\Xi_c^+\to\Xi_c^0\ell^+ \nu_\ell$ for $\ell=e,\mu$. In particular, we obtain $\Gamma(\Xi_c^0 \to \Xi^- e^+ \nu_e)/|V_{cs}|^2 = 0.2515(73)\text{ ps}^{-1}$ and $\mathcal{B}(\Xi_c^0 \to \Xi^- e^+ \nu_e) = 3.58(12)\:\%$. These values are higher than those predicted by a previous lattice calculation and substantially higher than the experimentally measured values, but consistent with expectations from approximate $SU(3)$ flavor symmetry.