Doubly-charmed baryon production in $Z$ boson decay
In this paper, we carry out a detailed study of doubly-charmed baryon production in $Z$ boson decay, on the basis of the nonrelativistic QCD factorization. With the inclusion of the di-quark states $(cc)[^3S_1]_{\bar{\textbf{3}}}$ and $(cc)[^1S_0]_{{\textbf{6}}}$, the branching ratio of $\mathcal{B}_{Z \to \Xi_{cc}+X}$ is predicted to be of the $10^{-5}$ order, indicating its experimental measurability. By comparing to the $\Lambda^{+}_{c}$ yield in $Z$ decay, we predict $\mathcal{R}_{\Xi_{cc}^{+}}(=\frac{\Gamma(Z \to \Xi^{+}_{cc}) \times \mathcal{B}(\Xi^{+}_{cc} \to \Lambda_c^{+}K^{-}\pi^{+})}{\Gamma(Z \to \Lambda_c^{+})})=(0.85^{+0.10}_{-0.07}) \times 10^{-4}$ and $\mathcal{R}_{\Xi_{cc}^{++}}(=\frac{\Gamma(Z \to \Xi^{++}_{cc}) \times \mathcal{B}(\Xi^{++}_{cc} \to \Lambda_c^{+}K^{-}\pi^{+}\pi^{+})}{\Gamma(Z \to \Lambda_c^{+})})=(1.70^{+0.20}_{-0.14}) \times 10^{-4}$, which are at clear variance with the SELEX measurements but comparable with the values given by the LHCb and Belle collaborations.