CMS-PAS-BPH-18-005

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.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 12 (2019) 100. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	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.
png pdf	Figure 3: The illustration of decay angles in ${{\mathrm {B}^{+}}}\to {\mathrm {J}/\psi} {{\overline {\Lambda}}} {\mathrm {p}}$ decay.
png pdf	Figure 4: The background-subtracted and efficiency-corrected $\cos(\theta _{{{\mathrm {K}}} ^{*}})$ distribution on data and simulation.
png pdf	Figure 5: The dependence of first unnormalized Legendre moments on $M( {{\overline {\Lambda}}} {\mathrm {p}})$ .
png pdf	Figure 5-a: The dependence of the first unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$ .
png pdf	Figure 5-b: The dependence of the second unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$ .
png pdf	Figure 5-c: The dependence of the third unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$ .
png pdf	Figure 5-d: The dependence of the fourth unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$ .
png pdf	Figure 5-e: The dependence of the fifth unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$ .
png pdf	Figure 5-f: The dependence of the sixth unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$ .
png pdf	Figure 5-g: The dependence of the seventh unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$ .
png pdf	Figure 5-h: The dependence of the eighth unnormalized Legendre moment on $M( {{\overline {\Lambda}}} {\mathrm {p}})$ .

Tables
png pdf	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.
png pdf	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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