Abstract

The $\Xi_b^0 \rightarrow \Xi_c^+ D_s^-$ and $\Xi_b^- \rightarrow \Xi_c^0 D_s^-$ decays are observed for the first time using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$, corresponding to an integrated luminosity of $5.1\mathrm{fb}^{-1}$. The relative branching fractions times the beauty-baryon production cross-sections are measured to be \begin{align*} \mathcal{R}\left(\frac{\Xi_b^0}{\Lambda_b^0}\right) \equiv \frac{\sigma\left(\Xi_b^0\right)}{\sigma\left(\Lambda_b^0\right)} \times \frac{\mathcal{B}\left(\Xi_b^0 \rightarrow \Xi_c^+ D_s^-\right)}{\mathcal{B}\left(\Lambda_b^0 \rightarrow \Lambda_c^0 D_s^-\right)} =(15.8\pm1.1\pm0.6\pm7.7)\%, \mathcal{R}\left(\frac{\Xi_b^-}{\Lambda_b^0}\right) \equiv \frac{\sigma\left(\Xi_b^-\right)}{\sigma\left(\Lambda_b^0\right)} \times \frac{\mathcal{B}\left(\Xi_b^- \rightarrow \Xi_c^0 D_s^-\right)}{\mathcal{B}\left(\Lambda_b^0 \rightarrow \Lambda_c^0 D_s^-\right)} =(16.9\pm1.3\pm0.9\pm4.3)\%, \end{align*} where the first uncertainties are statistical, the second systematic, and the third due to the uncertainties on the branching fractions of relevant charm-baryon decays. The masses of $\Xi_b^0$ and $\Xi_b^-$ baryons are measured to be $m_{\Xi_b^0}=5791.12\pm0.60\pm0.45\pm0.24\mathrm{MeV}/c^2$ and $m_{\Xi_b^-}=5797.02\pm0.63\pm0.49\pm0.29\mathrm{MeV}/c^2$, where the uncertainties are statistical, systematic, and those due to charm-hadron masses, respectively.

Figures and captions

Invariant-mass distributions of (top left) $\Lambda ^0_ b $ , (top right) $\Xi ^0_ b $ , and (bottom) $\Xi ^-_ b $ decays. The data are overlaid on the fit results.	mass_d[..].pdf [34 KiB] HiDef png [298 KiB] Thumbnail [206 KiB] *.C file
	mass_d[..].pdf [33 KiB] HiDef png [364 KiB] Thumbnail [253 KiB] *.C file
	mass_d[..].pdf [30 KiB] HiDef png [307 KiB] Thumbnail [209 KiB] *.C file
Comparison of measured (red) $b$ baryon masses with (blue) the PDG values [2]. The mass of $\Lambda ^0_ b $ is shifted upward by 175 $\text{ Me V /}c^2$ to reduce the range of this plot. The inner (outer) error bar is for the statistical (total) uncertainty.	M.pdf [13 KiB] HiDef png [64 KiB] Thumbnail [56 KiB] *.C file
Measured $\mathcal{R}$ values. The inner (outer) error bar is for the statistical (total) uncertainty.	BF.pdf [14 KiB] HiDef png [44 KiB] Thumbnail [40 KiB] *.C file
Distributions of the $H_c$ mass versus the $ D ^-_ s $ mass with the regions 1--4 indicated. The regions illustrate the signal region and the $H_c$ and/or $ D ^-_ s $ sideband regions.	mDs_mX[..].pdf [42 KiB] HiDef png [319 KiB] Thumbnail [398 KiB] *.C file
	mDs_mX[..].pdf [44 KiB] HiDef png [907 KiB] Thumbnail [647 KiB] *.C file
	mDs_mX[..].pdf [21 KiB] HiDef png [495 KiB] Thumbnail [442 KiB] *.C file
Invariant-mass distributions of $\Lambda ^0_ b $ candidates in the (top left) region 1, (top right) region 2, and (bottom) region 3.	region1_lb.pdf [31 KiB] HiDef png [313 KiB] Thumbnail [229 KiB] *.C file
	region2_lb.pdf [32 KiB] HiDef png [323 KiB] Thumbnail [221 KiB] *.C file
	region3_lb.pdf [33 KiB] HiDef png [263 KiB] Thumbnail [230 KiB] *.C file
Invariant-mass distributions of $\Lambda ^0_ b $ candidates in the (top left) region 1, (top right) region 2, and (bottom) region 3.	region[..].pdf [29 KiB] HiDef png [222 KiB] Thumbnail [208 KiB] *.C file
	region[..].pdf [30 KiB] HiDef png [327 KiB] Thumbnail [238 KiB] *.C file
	region[..].pdf [30 KiB] HiDef png [218 KiB] Thumbnail [205 KiB] *.C file
Invariant-mass distributions of $\Lambda ^0_ b $ candidates in the (top left) region 1, (top right) region 2, and (bottom) region 3.	region[..].pdf [27 KiB] HiDef png [210 KiB] Thumbnail [186 KiB] *.C file
	region[..].pdf [28 KiB] HiDef png [299 KiB] Thumbnail [209 KiB] *.C file
	region[..].pdf [30 KiB] HiDef png [331 KiB] Thumbnail [236 KiB] *.C file
Animated gif made out of all figures.	PAPER-2023-017.gif Thumbnail

Tables and captions

Branching fractions of $H_c$ decays [2].	Table_1.pdf [68 KiB] HiDef png [60 KiB] Thumbnail [28 KiB] tex code
Systematic uncertainties on the relative branching fraction measurements. Results are given as relative uncertainties.	Table_2.pdf [78 KiB] HiDef png [78 KiB] Thumbnail [35 KiB] tex code
Systematic uncertainties for the $H_b$ mass measurements.	Table_3.pdf [83 KiB] HiDef png [38 KiB] Thumbnail [16 KiB] tex code
Systematic uncertainties for the $H_b$ mass-difference measurements.	Table_4.pdf [82 KiB] HiDef png [42 KiB] Thumbnail [18 KiB] tex code
Measured $H_b$ masses and mass differences and the previous world averages [2].	Table_5.pdf [76 KiB] HiDef png [49 KiB] Thumbnail [20 KiB] tex code

Created on 26 April 2024.