First observation of the ${\Lambda}_b^0$ → D⁺D⁻Λ decay

Abstract

The ${\Lambda}_b^0$ → D⁺D⁻Λ 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 TeV, corresponding to an integrated luminosity of 5.3 fb⁻¹. Using the B⁰ → ${D}^{+}{D}^{-}{K}_S^0$ decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be

$$ \mathcal{R}=\frac{\sigma_{\Lambda_b^0}}{\sigma_{B^0}}=\frac{\mathcal{B}\left({\Lambda}_b^0\to {D}^{+}{D}^{-}\Lambda \right)}{\mathcal{B}\left({B}^0\to {D}^{+}{D}^{-}{K}_{\textrm{S}}^0\right)}=0.179\pm 0.022\pm 0.014, $$

where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, $\mathcal{B}\left({B}^0\to {D}^{+}{D}^{-}{K}_{\textrm{S}}^0\right)$, and the cross-section ratio, ${\sigma}_{\Lambda_b^0}/{\sigma}_{B^0}$, previously measured by LHCb are used to derive the branching fraction of the ${\Lambda}_b^0$ → D⁺D⁻Λ decay

$$ \mathcal{B}\left({\Lambda}_b^0\to {D}^{+}{D}^{-}\Lambda \right)=\left(1.24\pm 0.15\pm 0.10\pm 0.28\pm 0.11\right)\times {10}^{-4}, $$

where the third and fourth contributions are due to uncertainties of $\mathcal{B}\left({B}^0\to {D}^{+}{D}^{-}{K}_{\textrm{S}}^0\right)$ and ${\sigma}_{\Lambda_b^0}/{\sigma}_{B^0}$, respectively. Inspection of the D⁺Λ and D⁺D⁻ invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The ${\Lambda}_b^0$ → D^*+D⁻Λ decay is also observed for the first time as a partially reconstructed component in the D⁺D⁻Λ invariant mass spectrum.