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 $4.8sigma$. 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 $12.1sigma$ 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.