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Observation of the $B^0_{s}\to\psi{(2\mathrm{S})}\eta$ and $B^0_{(s)}\to\psi{(2\mathrm{S})}\pi^+\pi^-$ decays

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Abstract

First observations of the $B^0_s \rightarrow \psi(2S) \eta$, $B^0 \rightarrow \psi(2S) \pi^+ \pi^-$ and $B^0_s \rightarrow \psi(2S) \pi^+ \pi^-$ decays are made using a dataset corresponding to an integrated luminosity of 1.0 $fb^{-1}$ collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=7$ TeV. The ratios of the branching fractions of each of the $\psi(2S)$ modes with respect to the corresponding $J/\psi$ decays are \[ \frac{\mathcal{B}(B^0_s \rightarrow \psi(2S) \eta) }{\mathcal{B}(B^0_s \rightarrow J/\psi \eta)} =0.83\pm0.14 (stat)\pm0.12 (syst)\pm0.02 (\mathcalB}), \] \[ \frac{\mathcal{B}(B^0 \rightarrow \psi(2S) \pi^+ \pi^-)}{\mathcal{B}(B^0 \rightarrow J/\psi \pi^+ \pi^-)} =0.56\pm0.07 (stat)\pm0.05 (syst)\pm0.01 (\mathcal{B}), \] \[ \frac{\mathcal{B}(B^0_s \rightarrow \psi(2S) \pi^+ \pi^-)}{\mathcal{B}(B^0_s \rightarrow J/\psi \pi^+ \pi^-)} =0.34\pm0.04 (stat)\pm0.03 (syst)\pm0.01 (\mathcal{B}), \] where the third uncertainty corresponds to the uncertainties of the dilepton branching fractions of the $J/\psi$ and $\psi(2S)$ meson decays.

Figures and captions

Mass distributions of (a) $ B ^{0}_{\mathrm{(s)}} \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \eta $ and (b) $ B ^{0}_{\mathrm{(s)}} \rightarrow \psi {(2\mathrm{S})} \eta $ candidates. The total fit function (solid black) and the combinatorial background (dashed) are shown. The solid red lines show the signal $ B ^0_ s $ contribution and the red dot dashed line corresponds to the $ B ^0$ contribution.

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Background subtracted (a) $\gamma \gamma $ and (b) $\mu ^+\mu ^- $ mass distributions in $ B ^0_ s \rightarrow \psi {(2\mathrm{S})} \eta $ decays. In both cases the blue line is the result of the fit described in the text.

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Mass distributions of (a) $ B ^{0}_{\mathrm{(s)}} \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+\pi ^- $ and (b) $ B ^{0}_{\mathrm{(s)}} \rightarrow \psi {(2\mathrm{S})} \pi ^+\pi ^- $ candidates. The total fit function (solid black) and the combinatorial background (dashed) are shown. The solid red lines show the signal $ B ^0_ s $ contribution and the red dot dashed lines correspond to the $ B ^0$ contributions. The reflections from misidentified $ B ^0 \rightarrow \psi K ^{*0} $, $ K ^{*0} \rightarrow K ^+ \pi ^- $ decays are shown with dotted blue lines.

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Background subtracted $\pi ^+\pi ^-$ mass distribution in (a) $ B ^0 \rightarrow \psi {(2\mathrm{S})} \pi ^+\pi ^- $ and (b) $ B ^0_ s \rightarrow \psi {(2\mathrm{S})} \pi ^+\pi ^- $ (black points). The red filled area shows the expected signal spectrum for the $\psi {(2\mathrm{S})}$ channel derived from the measured spectrum of the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ channel (the fit has one parameter --- the normalisation). The width of the band corresponds to the uncertainties of the distribution from the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ channel. In case of $ B ^0 \rightarrow \psi {(2\mathrm{S})} \pi ^+\pi ^- $, the blue vertical filled area shows the $ K ^0_{\rm\scriptscriptstyle S}$ region that is excluded from the fit.

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Animated gif made out of all figures.

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Tables and captions

Fitted values of signal events ($N_{\mathrm{B}}$), signal peak position ($\mathrm{M}_{\mathrm{B}}$) and resolution ($\sigma_{\mathrm{B}}$). The quoted uncertainties are statistical only.

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Fitted values of signal events ($N_{\mathrm{B}}$), signal peak position ($\mathrm{M}_{\mathrm{B}}$) and resolution ($\sigma_{\mathrm{B}}$). The quoted uncertainties are statistical only.

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Relative systematic uncertainties (in %) of the relative branching fractions.

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Created on 26 April 2024.