Study of $B_c^+\to J/\psi D_s^+$ and $B_c^+\to J/\psi D_s^{*+}$ decays in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
A study of $B_c^+\to J/\psi D_s^+$ and $B_c^+\to J/\psi D_s^{*+}$ decays using 139 fb$^{-1}$ of integrated luminosity collected with the ATLAS detector from $\sqrt{s} = 13$ TeV $pp$ collisions at the LHC is presented. The ratios of the branching fractions of the two decays to the branching fraction of the $B_c^+\to J/\psi \pi^+$ decay are measured: $\mathcal B(B_c^+\to J/\psi D_s^+)/\mathcal B(B_c^+\to J/\psi \pi^+) = 2.76\pm 0.47$ and $\mathcal B(B_c^+\to J/\psi D_s^{*+})/\mathcal B(B_c^+\to J/\psi \pi^+) = 5.33\pm 0.96$. The ratio of the branching fractions of the two decays is found to be $\mathcal B(B_c^+\to J/\psi D_s^{*+})/\mathcal B(B_c^+\to J/\psi D_s^+) = 1.93\pm0.26$. For the $B_c^+\to J/\psi D_s^{*+}$ decay, the transverse polarization fraction, $\Gamma_{\pm\pm}/\Gamma$, is measured to be $0.70\pm0.11$. The reported uncertainties include both the statistical and systematic components added in quadrature. The precision of the measurements exceeds that in all previous studies of these decays. These results supersede those obtained in the earlier ATLAS study of the same decays with $\sqrt{s} = 7$ and 8 TeV $pp$ collision data. A comparison with available theoretical predictions for the measured quantities is presented.
3 March 2022
e-print arXiv:2203.01808 - pdf from arXiv
Figures
Figure 01a
Feynman diagrams for Bc+→J/ψDs(*)+ decays: (a) colour-favoured spectator, (b) colour-suppressed spectator, and (c) annihilation topology.
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Figure 01b
Feynman diagrams for Bc+→J/ψDs(*)+ decays: (a) colour-favoured spectator, (b) colour-suppressed spectator, and (c) annihilation topology.
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Figure 01c
Feynman diagrams for Bc+→J/ψDs(*)+ decays: (a) colour-favoured spectator, (b) colour-suppressed spectator, and (c) annihilation topology.
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Figure 02a
Distributions of ((a), (c)) the J/ψDs+ mass and ((b), (d)) |cosθ′(μ+)| for the selected Bc+→J/ψDs(*)+ candidates in ((a), (b)) Dataset 1 and ((c), (d)) Dataset 2. Data are shown as points, and the overall result of the fit is given by the red solid curve. The purple dashed line shows the contribution of the Bc+→J/ψDs+ signal, while the orange dotted and blue dashed-dotted lines show the contributions of the A±± and A00 components of the Bc+→J/ψDs*+ signal, respectively. The background contribution is shown with the green long-dashed line. The bottom panels show the pulls, defined as the difference between the data and the fit function divided by the uncertainty of the data point.
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Figure 02b
Distributions of ((a), (c)) the J/ψDs+ mass and ((b), (d)) |cosθ′(μ+)| for the selected Bc+→J/ψDs(*)+ candidates in ((a), (b)) Dataset 1 and ((c), (d)) Dataset 2. Data are shown as points, and the overall result of the fit is given by the red solid curve. The purple dashed line shows the contribution of the Bc+→J/ψDs+ signal, while the orange dotted and blue dashed-dotted lines show the contributions of the A±± and A00 components of the Bc+→J/ψDs*+ signal, respectively. The background contribution is shown with the green long-dashed line. The bottom panels show the pulls, defined as the difference between the data and the fit function divided by the uncertainty of the data point.
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Figure 02c
Distributions of ((a), (c)) the J/ψDs+ mass and ((b), (d)) |cosθ′(μ+)| for the selected Bc+→J/ψDs(*)+ candidates in ((a), (b)) Dataset 1 and ((c), (d)) Dataset 2. Data are shown as points, and the overall result of the fit is given by the red solid curve. The purple dashed line shows the contribution of the Bc+→J/ψDs+ signal, while the orange dotted and blue dashed-dotted lines show the contributions of the A±± and A00 components of the Bc+→J/ψDs*+ signal, respectively. The background contribution is shown with the green long-dashed line. The bottom panels show the pulls, defined as the difference between the data and the fit function divided by the uncertainty of the data point.
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Figure 02d
Distributions of ((a), (c)) the J/ψDs+ mass and ((b), (d)) |cosθ′(μ+)| for the selected Bc+→J/ψDs(*)+ candidates in ((a), (b)) Dataset 1 and ((c), (d)) Dataset 2. Data are shown as points, and the overall result of the fit is given by the red solid curve. The purple dashed line shows the contribution of the Bc+→J/ψDs+ signal, while the orange dotted and blue dashed-dotted lines show the contributions of the A±± and A00 components of the Bc+→J/ψDs*+ signal, respectively. The background contribution is shown with the green long-dashed line. The bottom panels show the pulls, defined as the difference between the data and the fit function divided by the uncertainty of the data point.
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Figure 03
Distributions of the J/ψπ+ mass for the selected Bc+→J/ψπ+ candidates. Data are shown as points, and the overall result of the fit is given by the red solid curve. The signal contribution is shown by the purple shaded area. The blue dashed, red dotted, and green long-dashed lines correspond to the Bc+→J/ψρ+, Bc+→J/ψ K+, and combinatorial background contributions, respectively. The bottom panel shows the pulls, defined as the difference between the data and the fit function divided by the uncertainty of the data point.
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Figure 04
Comparison of the results of this measurement with those of ATLAS Run 1, LHCb and theoretical predictions based on a QCD relativistic potential model (QCD PM), QCD sum rules (QCD SR), covariant confined quark model (CCQM), Bauer&endash;Stech&endash;Wirbel relativistic quark model (BSW), light-front quark model (LFQM), perturbative QCD (pQCD), relativistic independent quark model (RIQM), and calculations in the QCD factorization approach (FNCM). Hatched areas show the statistical uncertainties of this measurement and yellow bands correspond to the total uncertainties. Quadrature sums of all experimental uncertainties are quoted for the ATLAS Run 1 and LHCb results. The uncertainties of the theoretical predictions are shown only if they are explicitly quoted in the corresponding papers.
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Tables
Table 01
Parameters of the Bc+→J/ψDs+ and Bc+→J/ψDs*+ signals obtained with the unbinned extended maximum-likelihood fit to the data. Only the statistical uncertainties are included. No acceptance or efficiency corrections are applied to the signal yields.
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Table 02
Parameters of the Bc+→J/ψπ+ signal obtained with the unbinned extended maximum-likelihood fit. Only the statistical uncertainties are included. No efficiency correction is applied to the signal yield.
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Table 03
Summary of the total efficiencies. Quoted uncertainties correspond to statistical uncertainties of the simulated samples used. For the Bc+→J/ψπ+ channel, the efficiency εBc+→J/ψπ+ entering the equations for RDs(*)+/π+ is shown, while the efficiency for the full dataset is not defined.
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Table 05
Comparison of the measured quantities with the results of earlier measurements and theory predictions. Values of the corresponding ratios of branching fractions calculated using Eqs. (4)–(6) and Eq. (7) and of transverse polarization fractions for B+, B0, and B0s decays are also shown. No phase-space corrections are applied to the ratios and the quoted uncertainties are the ones propagated from the world average uncertainties of the individual decay branching fractions. For all experimental measurements, quadrature sums of all uncertainties are quoted. Uncertainties in the predictions are quoted only if they are explicitly given in the corresponding references.
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Auxiliary material
Figure 01
Distributions of the BDT output for the data sidebands events (black points) and simulated signal events in Bc+→J/ψDs+ channel (purple dashed line) and A±± (orange dotted line) and A00 (blue dashed line) components of the Bc+→J/ψDs*+ signal. All distributions are normalised to unity. Events with the BDT output value above 0.04 are retained for the signal fit.
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Figure 02a
The projections of the fit on the |cosθ′(μ+)| variable for a subset of the selected Bc+→J/ψDs(*)+ candidates in a mass range 5950 MeV < m(J/ψDs+) < 6350 MeV in (a) Dataset 1 and (b) Dataset 2. Data are shown as points, and the overall result of the fit projection is given by the red solid curve. The purple dashed line shows the contribution of the Bc+→J/ψDs+ signal, while the orange dotted and blue dashed-dotted lines show the contributions of the A±± and A00 components of the Bc+→J/ψDs*+ signal, respectively. The background contribution is shown with green long-dashed line. The bottom panel shows the pulls, defined as the difference between the data and the fit function divided by the uncertainty of the data point.
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Figure 02b
The projections of the fit on the |cosθ′(μ+)| variable for a subset of the selected Bc+→J/ψDs(*)+ candidates in a mass range 5950 MeV < m(J/ψDs+) < 6350 MeV in (a) Dataset 1 and (b) Dataset 2. Data are shown as points, and the overall result of the fit projection is given by the red solid curve. The purple dashed line shows the contribution of the Bc+→J/ψDs+ signal, while the orange dotted and blue dashed-dotted lines show the contributions of the A±± and A00 components of the Bc+→J/ψDs*+ signal, respectively. The background contribution is shown with green long-dashed line. The bottom panel shows the pulls, defined as the difference between the data and the fit function divided by the uncertainty of the data point.
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Figure 03
Comparison of the measured ratios of branching fractions and the transverse polarisation fraction with the corresponding values for B+, B0, and B0s decays occurring predominantly via the colour-favoured or colour-suppressed spectator diagrams. No phase-space corrections are applied to the ratios of branching fractions and the quoted uncertainties are the ones propagated from the world average uncertainties of the individual decay branching fractions. Hatched areas show the statistical uncertainties of the measurement and yellow bands correspond to the total uncertainties. The results of the LHCb measurement are also shown with total experimental uncertainties.
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