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Study of $B^+_c$ decays to the $K^+K^-\pi^+$ final state and evidence for the decay $B^+_c\to\chi_{c0}\pi^+$

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Abstract

A study of $B_c^+\to K^+K^-\pi^+$ decays is performed for the first time using data corresponding to an integrated luminosity of 3.0 $\mathrm{fb}^{-1}$ collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of $7$ and $8$ TeV. Evidence for the decay $B_c^+\to\chi_{c0}(\to K^+K^-)\pi^+$ is reported with a significance of 4.0 standard deviations, resulting in the measurement of $\frac{\sigma(B_c^+)}{\sigma(B^+)}\times\mathcal{B}(B_c^+\to\chi_{c0}\pi^+)$ to be $(9.8^{+3.4}_{-3.0}(\mathrm{stat})\pm 0.8(\mathrm{syst}))\times 10^{-6}$. Here $\mathcal{B}$ denotes a branching fraction while $\sigma(B_c^+)$ and $\sigma(B^+)$ are the production cross-sections for $B_c^+$ and $B^+$ mesons. An indication of $\bar b c$ weak annihilation is found for the region $m(K^-\pi^+)<1.834\mathrm{\,GeV\!/}c^2$, with a significance of 2.4 standard deviations.

Figures and captions

Fit to the $ K ^+ K ^- \pi ^+ $ invariant mass for the $ B ^+ $ candidates, with $1.834<m( K ^+ K ^- )<1.894 {\mathrm{\,GeV\!/}c^2} $. The contributions from the signal $ B ^+ \rightarrow {\overline D}^0(\rightarrow K ^+ K ^- )\pi ^+ $, combinatorial background (Comb.) and partially reconstructed background (Part.) obtained from the fit are shown.

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Projection of the fit to the $ K ^+ K ^- \pi ^+ $ invariant mass in the $ B _ c ^+$ region, in the bins of BDT output used in the analysis: (top) $0.04<\mathcal{O}_{\mathrm{BDT}}<0.12$, (middle) $0.12<\mathcal{O}_{\mathrm{BDT}}<0.18$ and (bottom) $\mathcal{O}_{\mathrm{BDT}}>0.18$, for $m( K ^- \pi ^+ )<1.834 {\mathrm{\,GeV\!/}c^2} $, including the vetoes in $m( K ^+ K ^- )$ (see text). Apart from the signal type, which is given by $ B _ c ^+ \rightarrow K ^+ K ^- \pi ^+ $, the contributions are indicated according to the same scheme as in Fig. 1.

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Distribution of events for the signal region $6.2<m( K ^+ K ^- \pi ^+ )<6.35 {\mathrm{\,GeV\!/}c^2} $ in the $m^2( K ^- \pi ^+ )$ vs. $m^2( K ^+ K ^- )$ plane for (left) $\mathcal{O}_{\mathrm{BDT}}>0.12$ and (right) $\mathcal{O}_{\mathrm{BDT}}>0.18$. The vertical red dashed lines represent a band of width $\pm60 {\mathrm{\,MeV\!/}c^2} $ around the $\chi _{ c 0}$ mass. The horizontal blue dot-dashed line indicates the upper bound of the annihilation region at $m( K ^- \pi ^+ )=1.834 {\mathrm{\,GeV\!/}c^2} $, representing 17% of the available phase space area.

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Fit projections to the (left) $ K ^+ K ^- \pi ^+ $ and (right) $ K ^+ K ^- $ invariant masses, in the bins of BDT output (top) $0.04<\mathcal{O}_{\mathrm{BDT}}<0.12$, (middle) $0.12<\mathcal{O}_{\mathrm{BDT}}<0.18$ and (bottom) $\mathcal{O}_{\mathrm{BDT}}>0.18$, for the extraction of the $ B _ c ^+ \rightarrow \chi _{ c 0} (\rightarrow K ^+ K ^- )\pi ^+ $ signal. The contributions from the $ B _ c ^+ \rightarrow \chi _{ c 0} (\rightarrow K ^+ K ^- )\pi ^+ $ signal, combinatorial background (Comb.), possible pollution from the annihilation region $ B _ c ^+ \rightarrow ( K ^- \pi ^+ ) K ^+ $, and combinations of $\chi _{ c 0} \rightarrow K ^+ K ^- $ with a random track $X$ are shown.

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Tables and captions

Relative systematic uncertainties (in %) of the measurements of $R_{\mathrm{an},KK\pi}$ and $R_{\chi _{ c 0} \pi}$.

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Supplementary Material [file]

Supplementary material full pdf

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README for supplemental material: - supplementary.pdf is the compiled version - supplement.tex is the latex source file - feyn_diags.zip contains all the Feynman diagrams of Figure 1 - all the other figures have self-explanatory names

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Created on 18 December 2018.Citation count from INSPIRE on 18 December 2018.