Using proton-proton collision data, corresponding to an integrated luminosity of $9fb^{-1}$ collected with the LHCb detector, seven decay modes of the $B_c^+$ meson into a $J/\psi$ or $\psi(2S)$ meson and three charged hadrons, kaons or pions, are studied. The decays $B_c^+\rightarrow ( \psi(2S) \rightarrow J/\psi \pi^+ \pi^-)\pi^+ $, $B_c^+\rightarrow \psi(2S)\pi^+\pi^+\pi^-$, $B_c^+\rightarrow J/\psi K^+\pi^+\pi^-$ and $B_c^+\rightarrow K^+K^+K^-$ are observed for the first time, and evidence for the $B_c^+\rightarrow \psi(2S)K^+K^-\pi^+$ decay is found, where $J/\psi$ and $\psi(2S)$ mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different $B_c^+$ decays are reported as well as the fractions of the decays proceeding via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays.
Mass distributions for selected $ B _ c ^+ \rightarrow \psi 3 h ^{\pm} $ candidates. Projections of a fit, described in the text, are overlaid. |
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Distributions of the (left) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ $\pi ^+$ $\pi ^-$ $\pi ^+$ and (right) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ $\pi ^+$ $\pi ^-$ masses for selected $ B _ c ^+ \rightarrow \left(\psi {\rm{(2S)}} \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ \pi ^- \right)\pi ^+ $ candidates. Projections of a fit, described in the text, are overlaid. The right plot corresponds to the mass range $6.24<m_{ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ \pi ^- \pi ^+ }<6.31\text{ Ge V /}c^2 $. |
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Background-subtracted (left) $\pi ^+ \pi ^- \pi ^+ $ and (right) $\pi ^+ \pi ^- $ mass distributions for selected $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ \pi ^- \pi ^+ $ candidates. In the left plot the expectation from simulation for the $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} a _1(1260)^+ $ decays with BLL model [26,28,43] is overlaid. |
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Background-subtracted (left) $ K ^- \pi ^+ $ and (right) $ K ^+ K ^- $ mass distributions for selected $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ K ^- \pi ^+ $ candidates. The $ K ^+ K ^- $ mass spectrum is fitted in the full accessible $ K ^+$ $ K ^-$ mass region, $m_{ K ^+ K ^- }<2.923\text{ Ge V /}c^2 $. For better visibility, only a lowdash-mass part of the spectrum is shown. |
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Background-subtracted mass distributions of (left) $ K ^+ \pi ^- $ pairs for the selected $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ \pi ^- \pi ^+ $ candidates and (right) $ K ^+ K ^- $ combinations for the selected $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ K ^- K ^+ $ candidates. The $ K ^+ K ^- $ mass spectrum is fitted in the full accessible $ K ^+$ $ K ^-$ mass region, $m_{ K ^+ K ^- }<2.2\text{ Ge V /}c^2 $. For better visibility, only a lowdash-mass part of the spectrum is shown. |
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Animated gif made out of all figures. |
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Parameters of interest from the simultaneous unbinned extended maximum-likelihood fit. The uncertainties are statistical only. For previously unobserved decay modes, the last column shows the statistical significance estimated using pseudoexperiments in units of standard deviations. |
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Results for parameters from the fit to the backgrounddash-subtracted $\pi ^+ \pi ^- $ mass spectrum from the $ B _ c ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ \pi ^- \pi ^+ $ decays. The last row shows the statistical significance for the $ R$ structure estimated using Wilks' theorem [60]. |
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Ranges of relative systematic uncertainties for the ratios of branching fractions $\mathcal{R}^{ X }_{ Y }$. The total systematic uncertainty is the quadratic sum of individual contributions. |
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Systematic uncertainties for the fractions of the decays via resonances. |
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Comparison of the measured ratios $\mathcal{R}^{ X }_{ Y }$ with their theoretical predictions or derivations from previous measurements. |
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Comparison of the measured ratios of branching fractions for the Cabibbodash-suppressed and Cabibbodash-favoured decays with the ratios of branching fraction for similar decays of $ B _ c ^+$ , $ B ^+$ , $ B ^0$ and $ B ^0_ s $ mesons [14,52,70,71,72]. |
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Off-diagonal correlation coefficients ($\left[\%\right]$) for statistical uncertainties for the measured ratios $\mathcal{R}^{ X }_{ Y }$. |
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Off-diagonal correlation coefficients ($\left[\%\right]$) for systematic uncertainties for the measured ratios $\mathcal{R}^{ X }_{ Y }$. |
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Created on 26 April 2024.