Evidence for \(B^+ \rightarrow h_c K^+\) and observation of \(\eta_c(2S) \to p \bar{p} \pi^+ \pi^-\)

A search for the decays \(B^+ \rightarrow h_c K^+\) and \(B^0 \rightarrow h_c K_S^0\) is performed. Evidence for the decay \(B^+ \rightarrow h_c K^+\) is found; its significance is \(4.8\sigma\). No evidence is found for \(B^0 \rightarrow h_c K_S^0\). The branching fraction for \(B^+ \rightarrow h_c K^+\) is measured to be \((3.7^{+1.0}_{-0.9}{}^{+0.8}_{-0.8}) \times 10^{-5}\); the upper limit for the \(B^0 \rightarrow h_c K_S^0\) branching fraction is \(1.4 \times 10^{-5}\) at \(90\%\) C.L. In addition, a study of the \(p \bar{p} \pi^+ \pi^-\) invariant mass distribution in the channel \(B^+ \to (p \bar{p} \pi^+ \pi^-) K^+\) results in the first observation of the decay \(\eta_c(2S) \to p \bar{p} \pi^+ \pi^-\) with \(12.1\sigma\) significance. The analysis is based on the 711 \(\mathrm{fb}^{-1}\) data sample collected by the Belle detector at the asymmetric-energy \(e^+ e^-\) collider KEKB at the \(\Upsilon(4S)\) resonance.