Abstract

The $\Lambda^0_b \to D^+ D^- \Lambda$ decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of $13 \mathrm{TeV}$, corresponding to an integrated luminosity of $5.3 \mathrm{fb}^{-1}$. Using the $B^0 \to D^+ D^- K_{\mathrm{S}}^0$ decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be $$ {\cal R}=\frac{\sigma_{\Lambda^0_b}}{\sigma_{B^0}} \times \frac{{\cal B}(\Lambda^0_b \to D^+ D^- \Lambda)}{{\cal B}(B^0 \to D^+ D^- K_{\mathrm{S}}^0)}=0.179 \pm 0.022 \pm 0.014 $$ where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, ${\cal B}(B^0 \to D^+ D^- K_{\mathrm{S}}^0)$, and the cross-section ratio, $\sigma_{\Lambda^0_b} / \sigma_{B^0}$, previously measured by $\mathrm{LHCb}$ are used to derive the branching fraction of the $\Lambda^0_b \to D^+ D^- \Lambda$ decay $$ {\cal B}(\Lambda^0_b \to D^+ D^- \Lambda)=(1.24 \pm 0.15 \pm 0.10 \pm 0.28 \pm 0.11) \times 10^{-4}, $$ where the third and fourth contributions are due to uncertainties of ${\cal B}(B^0 \to D^+ D^- K_{\mathrm{S}}^0)$ and $\sigma_{\Lambda^0_b} / \sigma_{B^0}$, respectively. Inspection of the $D^+ \Lambda$ and $D^+ D^-$ invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The $\Lambda^0_b \to D^{*+} D^- \Lambda$ decay is also observed for the first time as a partially reconstructed component in the $D^+ D^- \Lambda$ invariant mass spectrum.

Figures and captions

Example diagrams resulting in intermediate states that might contribute to the $\Lambda ^0_ b \rightarrow D ^+ D ^- \Lambda $ decay.	Fig1_top.pdf [9 KiB] HiDef png [52 KiB] Thumbnail [29 KiB] *.C file
	Fig1_left.pdf [9 KiB] HiDef png [54 KiB] Thumbnail [28 KiB] *.C file
	Fig1_right.pdf [9 KiB] HiDef png [66 KiB] Thumbnail [37 KiB] *.C file
Invariant mass distribution of $\Lambda ^0_ b \rightarrow D ^+ D ^- \Lambda $ candidates near the signal region with the fit results superimposed, for the (left) $LL $ and (right) $DD $ categories, respectively.	Fig2_left.pdf [22 KiB] HiDef png [456 KiB] Thumbnail [280 KiB] *.C file
	Fig2_right.pdf [22 KiB] HiDef png [420 KiB] Thumbnail [267 KiB] *.C file
Invariant mass distribution of $ B ^0 \rightarrow D ^+ D ^- K ^0_{\mathrm{S}} $ candidates with the fit results superimposed, for the (left) $LL $ and (right) $DD $ categories, respectively.	Fig3_left.pdf [28 KiB] HiDef png [481 KiB] Thumbnail [305 KiB] *.C file
	Fig3_right.pdf [28 KiB] HiDef png [474 KiB] Thumbnail [294 KiB] *.C file
Normalized and background-subtracted invariant mass distributions of the (left) $ D ^+ \Lambda $, (right) $ D ^- \Lambda $ and (bottom) $ D ^+ D ^- $ systems in the $\Lambda ^0_ b \rightarrow D ^+ D ^- \Lambda $ decay, compared with the distributions in simulation samples.	Fig4_left.pdf [17 KiB] HiDef png [121 KiB] Thumbnail [70 KiB] *.C file
	Fig4_right.pdf [16 KiB] HiDef png [120 KiB] Thumbnail [70 KiB] *.C file
	Fig4_b[..].pdf [16 KiB] HiDef png [116 KiB] Thumbnail [65 KiB] *.C file
Normalized and background-subtracted invariant mass distributions of the (left) $ D ^\pm K ^0_{\mathrm{S}} $ and (right) $ D ^+ D ^- $ systems in the $ B ^0 \rightarrow D ^+ D ^- K ^0_{\mathrm{S}} $ decay, compared with the distributions in the simulation sample.	Fig5_left.pdf [17 KiB] HiDef png [127 KiB] Thumbnail [75 KiB] *.C file
	Fig5_right.pdf [17 KiB] HiDef png [112 KiB] Thumbnail [68 KiB] *.C file
Animated gif made out of all figures.	PAPER-2023-042.gif Thumbnail

Tables and captions

Summary of relative systematic uncertainties on the branching fraction measurement.

Table_1.pdf [36 KiB] HiDef png [71 KiB] Thumbnail [31 KiB] tex code

Supplementary Material [file]

Supplementary material full pdf	supple[..].pdf [2 MiB]
This ZIP file contains supplemetary material for the publication LHCb-PAPER-2023-042. The files are: supplementary.pdf : An overview of the extra figures supplementary.tex : Text file for the overview *.pdf, *.png, *.eps, *.C : The figures in various formats	Fig1_b[..].pdf [903 KiB] HiDef png [183 KiB] Thumbnail [157 KiB] *C file
	Fig1_l[..].pdf [933 KiB] HiDef png [180 KiB] Thumbnail [157 KiB] *C file
	Fig1_r[..].pdf [933 KiB] HiDef png [179 KiB] Thumbnail [157 KiB] *C file

Created on 17 May 2024.