A nonrelativistic quark model evaluation of exclusive $b\to c$ semileptonic decay of triply heavy baryons and $c\to s,d$ semileptonic decay of $cb$ baryons

TL;DR

This paper uses a nonrelativistic quark model to analyze semileptonic decays of triply and doubly heavy baryons, deriving heavy quark spin symmetry relations and predicting decay width ratios.

Contribution

It introduces the first heavy quark spin symmetry relations for these decays and assesses their accuracy across phase space, including effects of hyperfine mixing.

Findings

Heavy quark spin symmetry relations are valid near zero recoil.

Predicted decay width ratios are model-independent and reliable.

Hyperfine mixing significantly affects $c\to s,d$ decay widths in spin-1/2 $cb$ baryons.

Abstract

We present results for exclusive $b\to c$ semileptonic decays of ground state triply-heavy baryons and for semileptonic $c\to s,d$ decays of doubly heavy ground state $cb$ baryons. In both cases, we have derived for the first time heavy quark spin symmetry relations for the hadronic amplitudes near zero recoil. Though strictly valid in the limit of very large heavy quark masses and near zero recoil, they turn out to be reasonable accurate for the whole available phase space in these decays and for the actual heavy quark masses we use. With these relations we have made approximate, but model independent, predictions for ratios of decay widths. In the case of spin-1/2 $cb$ baryons, we find that hyperfine mixing in the wave function has a great impact on their $c\to s,d$ decay widths.