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

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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.

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Tables and captions

Relative systematic uncertainties.

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Created on 19 February 2021.