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

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## Abstract

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 $1.0 \invfb$ collected by the LHCb experiment. The branching fraction of $B_c^+ \to \psi(2S)\pi^+$ decays relative to that of the $B_c^+ \to J/\psi\pi^+$ 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 $\mathcal{B}(\psi(2S) \to \mu^+\mu^-)/\mathcal{B}(J/\psi \to \mu^+\mu^-)$.

## Figures and captions

 Invariant mass distributions of $B _ c ^+$ candidates reconstructed as (a) $B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+$ and (b) $B _ c ^+ \rightarrow \psi {(2S)} \pi ^+$. Points with error bars (black) show the data, the thick solid line (blue) represents the fit of the data, the dashed line (red) the signal distribution, the dotted line (green) the combinatorial background, the dot-dashed line (purple) the partially reconstructed background, and the thin solid line (light blue) the background from the $B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+$ channel. M_Jpsipi.eps [23 KiB] HiDef png [288 KiB] Thumbnail [245 KiB] *.C file M_Psipi.eps [18 KiB] HiDef png [261 KiB] Thumbnail [222 KiB] *.C file Animated gif made out of all figures. PAPER-2012-054.gif Thumbnail

## Tables and captions

 Relative systematic uncertainties. Table_1.pdf [17 KiB] HiDef png [78 KiB] Thumbnail [33 KiB] tex code

Created on 10 July 2020.