First observation of the decay $\Lambda_b^0 \to \eta_c(1S) p K^-$

TL;DR

This paper reports the first observation of the decay b0 b0 b0 b0 using LHCb data, measures its branching fraction, and searches for pentaquark states without evidence, setting upper limits.

Contribution

It presents the first observation and measurement of the b0 b0 b0 b0 decay and investigates pentaquark states in this decay channel.

Findings

First observation of b0 b0 b0 b0 decay.

Measured branching fraction of b0 b0 b0 b0.

No evidence for P_c(4312)^+ pentaquark, upper limit set.

Abstract

The decay $\Lambda_b^0 \to \eta_c(1S) p K^-$ is observed for the first time using a data sample of proton-proton collisions, corresponding to an integrated luminosity of 5.5 $fb^{-1}$, collected with the LHCb experiment at a center-of-mass energy of 13 TeV. The branching fraction of the decay is measured, using the $\Lambda_b^0 \to J/\psi p K^-$ decay as a normalization mode, to be $\mathcal{B}(\Lambda_b^0 \to \eta_c(1S) p K^-)=(1.06\pm0.16\pm0.06^{+0.22}_{-0.19})\times10^{-4}$, where the quoted uncertainties are statistical, systematic and due to external inputs, respectively. A study of the $\eta_c(1S) p$ mass spectrum is performed to search for the $P_c(4312)^+$ pentaquark state. No evidence is observed and an upper limit of \begin{equation*} \frac{\mathcal{B}(\Lambda_b^0 \to P_c(4312)^+ K^-)\times \mathcal{B}(P_c(4312)^+ \to \eta_c(1S) p)}{\mathcal{B}(\Lambda_b^0 \to \eta_c(1S) p K^-)} < 0.24 \end{equation*} is obtained at the 95% confidence level.