Observation of Ξb0→Ξc+Ds- and Ξb-→Ξc0Ds- decays

Abstract

The ${\mathrm{\Xi }}_b^0\to {\mathrm{\Xi }}_c^{+}{D}_s^{-}$ and ${\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}_c^0{D}_s^{-}$ decays are observed for the first time using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=13\text{TeV}$, corresponding to an integrated luminosity of $5.1{\text{fb}}^{-1}$. The branching fractions times the production cross-sections of ${\mathrm{\Xi }}_b$ baryons relative to that of ${\mathrm{\Lambda }}_b^0$ baryon are measured to be $$\begin{array}{cc}\hfill \mathcal{R}\left(\frac{{\mathrm{\Xi }}_b^0}{{\mathrm{\Lambda }}_b^0}\right)& \equiv \frac{\sigma \left({\mathrm{\Xi }}_b^0\right)}{\sigma \left({\mathrm{\Lambda }}_b^0\right)}\times \frac{\mathcal{B}\left({\mathrm{\Xi }}_b^0,\to ,{\mathrm{\Xi }}_c^{+},D_s^{-}\right)}{\mathcal{B}\left({\mathrm{\Lambda }}_b^0,\to ,{\mathrm{\Lambda }}_c^0,D_s^{-}\right)}\hfill \\ \hfill & =(15.8\pm 1.1\pm 0.6\pm 7.7)\%,\hfill \\ \hfill \mathcal{R}\left(\frac{{\mathrm{\Xi }}_b^{-}}{{\mathrm{\Lambda }}_b^0}\right)& \equiv \frac{\sigma \left({\mathrm{\Xi }}_b^{-}\right)}{\sigma \left({\mathrm{\Lambda }}_b^0\right)}\times \frac{\mathcal{B}\left({\mathrm{\Xi }}_b^{-},\to ,{\mathrm{\Xi }}_c^0,D_s^{-}\right)}{\mathcal{B}\left({\mathrm{\Lambda }}_b^0,\to ,{\mathrm{\Lambda }}_c^0,D_s^{-}\right)}\hfill \\ \hfill & =(16.9\pm 1.3\pm 0.9\pm 4.3)\%,\hfill \end{array}$$where the first uncertainties are statistical, the second systematic, and the third due to the uncertainties on the decay branching fractions of relevant charmed baryons. The masses of ${\mathrm{\Xi }}_b^0$ and ${\mathrm{\Xi }}_b^{-}$ baryons are measured to be $m_{{\mathrm{\Xi }}_b^0}=5791.12\pm 0.60\pm 0.45\pm 0.24\text{MeV}/c^2$ and $m_{{\mathrm{\Xi }}_b^{-}}=5797.02\pm 0.63\pm 0.49\pm 0.29\text{MeV}/c^2$, where the uncertainties are statistical, systematic, and those due to charmed-hadron masses, respectively.