Search for the $\Lambda_b^0 \rightarrow \Lambda \eta^\prime$ and $\Lambda_b^0\rightarrow \Lambda \eta$ decays with the LHCb detector

A search is performed for the as yet unobserved baryonic $\Lambda_b^0 \rightarrow \Lambda \eta^\prime$ and $\Lambda_b^0 \rightarrow \Lambda \eta$ decays with 3$fb^{-1}$ of proton-proton collision data recorded by the LHCb experiment. The $B^0 \rightarrow K_S^0 \eta^\prime$ decay is used as a normalisation channel. No significant signal is observed for the $\Lambda_b^0 \rightarrow \Lambda \eta^\prime$ decay. An upper limit is found on the branching fraction of $\mathcal{B}(\Lambda_b^0 \rightarrow \Lambda \eta^\prime)<3.1\times10^{-6}$ at 90% confidence level. Evidence is seen for the presence of the $\Lambda_b^0 \rightarrow \Lambda \eta$ decay at the level of $3\sigma$ significance, with a branching fraction $\mathcal{B}(\Lambda_b^0 \rightarrow \Lambda \eta)=(9.3^{+7.3}_{-5.3})\times10^{-6}$.