Observation of the decay $B_c^{+}\to \psi (2S){\pi }^{+}$

The decay $B_c^{+}\to \psi (2S){\pi }^{+}$ with $\psi (2S)\to {\mu }^{+}{\mu }^{-}$ is observed with a significance of $5.2\sigma$ using $pp$ collision data corresponding to an integrated luminosity of $1.0\text{invfb}$ collected by the LHCb experiment. The branching fraction of $B_c^{+}\to \psi (2S){\pi }^{+}$ decays relative to that of the $B_c^{+}\to J\mathrm{/}\psi {\pi }^{+}$ mode is measured to be \begin{equation*} \frac{$\mathcal{B}$(B_c^+ \to \psi(2S)\pi^+)}{$\mathcal{B}$(B_c^+ \to J/\psi\pi^+)} = 0.250 \pm 0.068 ,$\text{stat}$ \pm 0.014 ,$\text{syst}$ \pm 0.006 ,($\mathcal{B}$). \end{equation*} The last term is the uncertainty on the ratio $$\mathcal{B}$(\psi(2S) \to \mu^+\mu^-)/$\mathcal{B}$(J/\psi \to \mu^+\mu^-)$.