Study of $ {\mathrm{B}}_{\mathrm{c}}^{+} $ decays to charmonia and three light hadrons

Information

LHCb-PAPER-2021-034
CERN-EP-2021-216
arXiv:2111.03001 [PDF]

(Submitted on 04 Nov 2021)
JHEP 01 (2022) 065
Inspire 1960979

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Abstract

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.

Figures and captions

Mass distributions for selected $ B _ c ^+ \rightarrow \psi 3 h ^{\pm} $ candidates. Projections of a fit, described in the text, are overlaid.	Fig_1.pdf [244 KiB] HiDef png [695 KiB] Thumbnail [572 KiB] *.C file tex code
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 $.	Fig_2.pdf [157 KiB] HiDef png [273 KiB] Thumbnail [210 KiB] *.C file tex code
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.	Fig_3.pdf [175 KiB] HiDef png [279 KiB] Thumbnail [208 KiB] *.C file tex code
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.	Fig_4.pdf [161 KiB] HiDef png [260 KiB] Thumbnail [225 KiB] *.C file tex code
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.	Fig_5.pdf [159 KiB] HiDef png [245 KiB] Thumbnail [210 KiB] *.C file tex code
Animated gif made out of all figures.	PAPER-2021-034.gif Thumbnail

Tables and captions

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.	Table_1.pdf [87 KiB] HiDef png [98 KiB] Thumbnail [49 KiB] tex code
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].	Table_2.pdf [98 KiB] HiDef png [78 KiB] Thumbnail [32 KiB] tex code
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.	Table_3.pdf [63 KiB] HiDef png [126 KiB] Thumbnail [55 KiB] tex code
Systematic uncertainties for the fractions of the decays via resonances.	Table_4.pdf [82 KiB] HiDef png [101 KiB] Thumbnail [43 KiB] tex code
Comparison of the measured ratios $\mathcal{R}^{ X }_{ Y }$ with their theoretical predictions or derivations from previous measurements.	Table_5.pdf [84 KiB] HiDef png [102 KiB] Thumbnail [51 KiB] tex code
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].	Table_6.pdf [92 KiB] HiDef png [130 KiB] Thumbnail [66 KiB] tex code
Off-diagonal correlation coefficients ($\left[\%\right]$) for statistical uncertainties for the measured ratios $\mathcal{R}^{ X }_{ Y }$.	Table_7.pdf [63 KiB] HiDef png [75 KiB] Thumbnail [37 KiB] tex code
Off-diagonal correlation coefficients ($\left[\%\right]$) for systematic uncertainties for the measured ratios $\mathcal{R}^{ X }_{ Y }$.	Table_8.pdf [64 KiB] HiDef png [78 KiB] Thumbnail [39 KiB] tex code