Four decay modes of the $B_c^+$ meson into a $J/\psi$ meson and multiple charged kaons or pions are studied using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV and corresponding to an integrated luminosity of $9$ fb$^{-1}$. The decay $B_c^+\to J/\psi K^+ K^- \pi^+ \pi^+ \pi^-$ is observed for the first time, and evidence for the $B_c^+\to J/\psi 4\pi^+ 3\pi^-$ decay is found. The decay $B_c^+\to J/\psi 3\pi^+ 2\pi^-$ is observedand and the previous observation of the $B_c^+\to\psi(2S) \pi^+ \pi^+ \pi^-$ decay is confirmed using the $\psi(2S) \to J/\psi \pi^+ \pi^-$ decay mode. Ratios of the branching fractions of these four $B_c^+$ decay channels are measured.
Mass distributions for selected (top left) $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } 3\pi ^+ 2\pi ^- $, (top right) $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^+ K ^- \pi ^+ \pi ^+ \pi ^- $ and (bottom) $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } 4\pi ^+ 3\pi ^- $ candidates. Projections of the fit, described in the text, are overlaid. |
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(left) Distribution of the $ { J \mskip -3mu/\mskip -2mu\psi } 3\pi ^+ 2\pi ^- $ mass for selected $ B _ c ^+ \rightarrow \psi {(2{\mathrm{S}})} \pi ^+ \pi ^+ \pi ^- $ candidates with the $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- $ mass between 3.679 and 3.692 $\text{ Ge V /}c^2$ . (right) Distribution of the $ { J \mskip -3mu/\mskip -2mu\psi } \pi ^+ \pi ^- $ mass for selected $ B _ c ^+ \rightarrow \psi {(2{\mathrm{S}})} \pi ^+ \pi ^+ \pi ^- $ candidates with the $ { J \mskip -3mu/\mskip -2mu\psi } 3\pi ^+ 2\pi ^- $ mass between 6.245 and 6.301 $\text{ Ge V /}c^2$ . Projections of the fit, described in the text, are overlaid. |
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Mass spectra for the lightdash-hadron system for the (top left) $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } 3\pi ^+ 2\pi ^- $, (top right) $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^+ K ^- \pi ^+ \pi ^+ \pi ^- $ and (bottom) $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } 4\pi ^+ 3\pi ^- $ decays. Expectations from the BLL model are overlaid. |
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Mass spectra for the $\pi ^+ \pi ^+ \pi ^- $ combinations from the (left) $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } 3\pi ^+ 2\pi ^- $ (6 entries per $ B _ c ^+$ candidate) and (right) $ B _ c ^+ \rightarrow \psi {(2{\mathrm{S}})} \pi ^+ \pi ^+ \pi ^- $ decays. The expectations from the BLL model are overlaid. |
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Background-subtracted $\pi ^+ \pi ^- $ mass distributions from (left) $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } 3\pi ^+ 2\pi ^- $ (6 entries per $ B _ c ^+$ candidate) and (right) $ B _ c ^+ \rightarrow \psi {(2{\mathrm{S}})} \pi ^+ \pi ^+ \pi ^- $ (2 entries per $ B _ c ^+$ candidate) decays. The results of the fits described in the text are overlaid. |
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Background-subtracted (left) $ K ^{\pm}\pi ^{\mp}$ (3 entries per $ B _ c ^+$ candidate) mass and (right) lowdash-mass part of the $ K ^+ K ^- $ mass distribution from the $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^+ K ^- \pi ^+ \pi ^+ \pi ^- $ decays. The results of the fit described in the text are overlaid on the left plot, while expectations from the BLL model are overlaid on the right plot. |
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Animated gif made out of all figures. |
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Signal yields obtained from the simultaneous unbinned extended maximumdash-likelihood fit. The uncertainties are statistical only. The last column shows the statistical significance estimated using Wilks' theorem, in units of standard deviations. |
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Ranges of relative systematic uncertainties for the various ratios of branching fractions, $\mathcal{R}^{ X }_{ Y }$. The total systematic uncertainty is the quadratic sum of individual contributions. |
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Off-diagonal correlation coefficients (in percent) for statistical and systematic uncertainties of the measured ratios $\mathcal{R}^{ X }_{ Y }$. |
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Created on 26 April 2024.