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| CMS-PAS-BPH-18-005 | ||
| Study of the $\mathrm{B}^{+}\rightarrow \mathrm{J}/\psi \bar{\Lambda} \mathrm{p}$ decay in proton-proton collisions at $\sqrt{s}= $ 8 TeV | ||
| CMS Collaboration | ||
| March 2019 | ||
| Abstract: A study of the $\mathrm{B}^{+} \rightarrow \mathrm{J}/\psi \bar{\Lambda} \mathrm{p}$ decay is reported, using proton-proton collision data collected at $\sqrt{s}= $ 8 TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 19.6 fb$^{-1}$. The ratio of branching fractions ${{\cal B}(\mathrm{B}^{+} \rightarrow \mathrm{J}/\psi \bar{\Lambda} \mathrm{p})}/{{\cal B}(\mathrm{B}^{+} \rightarrow \mathrm{J}/\psi \mathrm{K}^{*+})}$ is measured to be 1.054 $\pm$ 0.057 (stat) $\pm$ 0.028 (syst) $\pm$ 0.011 (${\cal B}$)%, where the first uncertainty is statistical, the second is systematic, and the third reflects the uncertainties in the world-average branching fractions. The invariant mass distributions of $\mathrm{J}/\psi \bar{\Lambda}$, $\mathrm{J}/\psi \mathrm{p}$, and $\bar{\Lambda} \mathrm{p}$ systems produced in the $\mathrm{B}^{+} \rightarrow \mathrm{J}/\psi \bar{\Lambda} \mathrm{p}$ decay are investigated and found to be inconsistent with the pure phase space hypothesis. The analysis is extended by using a model-independent angular amplitude analysis, which shows that the inclusion of contributions from excited kaons in the $\bar{\Lambda} \mathrm{p}$ system does improve the description of the observed invariant mass distributions. | ||
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Links:
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These preliminary results are superseded in this paper, JHEP 12 (2019) 100. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Invariant mass distribution of the selected $ {{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{\overline {\Lambda}}} {\mathrm {p}}$ candidates (upper). The $ {\mathrm {J}/\psi} {\mathrm {K^0_S}} {\pi ^+}$ (lower left) and $ {\mathrm {K^0_S}} {\pi ^+}$ (lower right) invariant mass distributions in the $ {{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{{\mathrm {K}}} ^{*+}} $ decay. The points are data and the curves are results of the fits described in the text. The vertical lines in the last plot indicate the $ {{{\mathrm {K}}} ^{*+}} $ invariant mass window used for the normalization, as described in the text. |
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Figure 1-a:
Invariant mass distribution of the selected $ {{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{\overline {\Lambda}}} {\mathrm {p}}$ candidates. The points are data and the curves are results of the fits described in the text. |
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Figure 1-b:
The $ {\mathrm {J}/\psi} {\mathrm {K^0_S}} {\pi ^+}$ invariant mass distribution in the $ {{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{{\mathrm {K}}} ^{*+}} $ decay. The points are data and the curves are results of the fits described in the text. |
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Figure 1-c:
The $ {\mathrm {K^0_S}} {\pi ^+}$ invariant mass distribution in the $ {{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{{\mathrm {K}}} ^{*+}} $ decay. The points are data and the curves are results of the fits described in the text. The vertical lines indicate the $ {{{\mathrm {K}}} ^{*+}} $ invariant mass window used for the normalization, as described in the text. |
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Figure 2:
The invariant mass distributions of the $ {\mathrm {J}/\psi} \, {\mathrm {p}}$ (upper left), $ {\mathrm {J}/\psi} {{\overline {\Lambda}}}$ (upper right), and $ {{\overline {\Lambda}}} {\mathrm {p}}$ (lower) systems from the $ {{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{\overline {\Lambda}}} {\mathrm {p}}$ decay. The points are efficiency-corrected and background-subtracted data. Superimposed curves are obtained from simulation: the red curve represents the phase space distribution corrected by the $ {{\overline {\Lambda}}} {\mathrm {p}}$ angular structure with the inclusion of the first eight moments corresponding to the resonances in the $ {{\overline {\Lambda}}} {\mathrm {p}}$ system with the maximum spin $S=4$; the dashed red curve is the fit to the phase space distribution reweighted according to the 1D $\cos\theta _{{{\mathrm {K}}} ^{*}}$ distribution, which is defined as the $H_1$ hypothesis and explained in Section 8.3; the black dashed line corresponds to the pure phase space fit. |
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Figure 2-a:
The invariant mass distribution of the $ {\mathrm {J}/\psi} \, {\mathrm {p}}$ system from the $ {{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{\overline {\Lambda}}} {\mathrm {p}}$ decay. The points are efficiency-corrected and background-subtracted data. Superimposed curves are obtained from simulation: the red curve represents the phase space distribution corrected by the $ {{\overline {\Lambda}}} {\mathrm {p}}$ angular structure with the inclusion of the first eight moments corresponding to the resonances in the $ {{\overline {\Lambda}}} {\mathrm {p}}$ system with the maximum spin $S=4$; the dashed red curve is the fit to the phase space distribution reweighted according to the 1D $\cos\theta _{{{\mathrm {K}}} ^{*}}$ distribution, which is defined as the $H_1$ hypothesis and explained in Section 8.3; the black dashed line corresponds to the pure phase space fit. |
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Figure 2-b:
The invariant mass distribution of the $ {\mathrm {J}/\psi} {{\overline {\Lambda}}}$ system from the $ {{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{\overline {\Lambda}}} {\mathrm {p}}$ decay. The points are efficiency-corrected and background-subtracted data. Superimposed curves are obtained from simulation: the red curve represents the phase space distribution corrected by the $ {{\overline {\Lambda}}} {\mathrm {p}}$ angular structure with the inclusion of the first eight moments corresponding to the resonances in the $ {{\overline {\Lambda}}} {\mathrm {p}}$ system with the maximum spin $S=4$; the dashed red curve is the fit to the phase space distribution reweighted according to the 1D $\cos\theta _{{{\mathrm {K}}} ^{*}}$ distribution, which is defined as the $H_1$ hypothesis and explained in Section 8.3; the black dashed line corresponds to the pure phase space fit. |
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Figure 2-c:
The invariant mass distribution of the $ {{\overline {\Lambda}}} {\mathrm {p}}$ system from the $ {{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{\overline {\Lambda}}} {\mathrm {p}}$ decay. The points are efficiency-corrected and background-subtracted data. Superimposed curves are obtained from simulation: the red curve represents the phase space distribution corrected by the $ {{\overline {\Lambda}}} {\mathrm {p}}$ angular structure with the inclusion of the first eight moments corresponding to the resonances in the $ {{\overline {\Lambda}}} {\mathrm {p}}$ system with the maximum spin $S=4$; the dashed red curve is the fit to the phase space distribution reweighted according to the 1D $\cos\theta _{{{\mathrm {K}}} ^{*}}$ distribution, which is defined as the $H_1$ hypothesis and explained in Section 8.3; the black dashed line corresponds to the pure phase space fit. |
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Figure 3:
The illustration of decay angles in $ {{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{\overline {\Lambda}}} {\mathrm {p}}$ decay. |
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Figure 4:
The background-subtracted and efficiency-corrected $\cos(\theta _{{{\mathrm {K}}} ^{*}})$ distribution on data and simulation. |
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Figure 5:
The dependence of first unnormalized Legendre moments on $M( {{\overline {\Lambda}}} {\mathrm {p}})$. |
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Figure 5-a:
The dependence of the first unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$. |
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Figure 5-b:
The dependence of the second unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$. |
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Figure 5-c:
The dependence of the third unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$. |
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Figure 5-d:
The dependence of the fourth unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$. |
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Figure 5-e:
The dependence of the fifth unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$. |
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Figure 5-f:
The dependence of the sixth unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$. |
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Figure 5-g:
The dependence of the seventh unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$. |
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Figure 5-h:
The dependence of the eighth unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$. |
| Tables | |
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Table 1:
Summary of the relative systematic uncertainties in the $ {{\cal B}({{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{\overline {\Lambda}}} {\mathrm {p}})} / {{\cal B}({{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{{\mathrm {K}}} ^{*+}})}$ ratio. |
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Table 2:
Known excited $ {{\mathrm {K}}} ^{*}$ states [3] that can decay to $ {{\overline {\Lambda}}} {\mathrm {p}}$. |
| Summary |
| Using the data set of proton-proton collisions, collected by the CMS experiment at $\sqrt{s} = $ 8 TeV and corresponding to an integrated luminosity of 19.6 fb$^{-1}$, we measured the branching fraction ratio ${{\cal B}(\mathrm{B^{+}} \to \mathrm{J}/\psi\bar{\Lambda} {\mathrm{p}})}/{{\cal B}(\mathrm{B^{+}} \to \mathrm{J}/\psi \mathrm{K}^{*+})} = $ (1.054 $\pm$ 0.057 (stat) $\pm$ 0.028 (syst) $\pm$ 0.011 (${\cal B}$) )$\times 10^{-2}$. Using the world-average branching fraction of the $\mathrm{B^{+}} \to \mathrm{J}/\psi \mathrm{K}^{*+}$ decay, we obtained ${\cal B}(\mathrm{B^{+}} \to \mathrm{J}/\psi\bar{\Lambda} {\mathrm{p}}) = $ (15.07 $\pm$ 0.81 (stat) $\pm$ 0.40 (syst) $\pm$ 0.86 (${\cal B}$) )$\times 10^{-6}$. The study of two-body invariant mass distributions of the $\mathrm{B^{+}} \to \mathrm{J}/\psi\bar{\Lambda} {\mathrm{p}}$ decay products was performed, showing that the spectra can not be satisfactory modeled with a phase space distribution. The incompatibility with the phase space hypothesis is more than 5.5, 6, and 3.4 standard deviations for the $\mathrm{J}/\psi \bar{\Lambda}$, $\mathrm{J}/\psi\,{\mathrm{p}}$, and $\bar{\Lambda} {\mathrm{p}}$ mass spectra, respectively. A model-independent approach was used to conclude that the agreement is improved significantly, and is within three standard deviations, once the contribution from K$^{*}$ resonances with spins up to 4 in the $\bar{\Lambda} {\mathrm{p}}$ system is accounted for. |
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