Origin of the Xi_c to Xi semileptonic branching-fraction discrepancy

Determine whether the discrepancy between the experimentally extracted and theoretically predicted branching fraction for the semileptonic decay Xi_c^0\to\Xi^-\ell^+\nu_\ell is caused by Xi_c\text{--}\Xi_c' configuration mixing, modified baryon wave-function overlap and recoil kinematics, or the normalization used in the experimental extraction.

Background

The paper compares the predicted branching fraction for the Cabibbo-favored decay $\Xi_c^0\to\Xi^-\ell^+\nu_\ell$ with the experimental average and finds a substantial discrepancy: the relativistic three-quark model and lattice-QCD calculations predict a considerably larger rate than the current experimental value. The $\Xi_c$ system is complicated by a strange spectator quark and possible coherent mixing between the flavor-antitriplet $\Xi_c$ and flavor-sextet $\Xi_c'$ configurations.

The authors identify several possible explanations that remain to be disentangled: configuration mixing, changes in the overlap and recoil behavior of the initial and final baryon wave functions, and the normalization procedure used to infer the absolute semileptonic branching fraction from ratios involving $\Xi_c^0\to\Xi^-\pi^+$. Resolving which mechanism is responsible requires improved theoretical analysis and more reliable experimental normalization and decay measurements.