CMS-BPH-19-002

CMS-BPH-19-002 ; CERN-EP-2019-224
Observation of the $\Lambda_{\mathrm{b}}^0 \to \mathrm{J}/\psi \Lambda \phi$ decay in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
9 November 2019
Phys. Lett. B 802 (2020) 135203
Abstract: The observation of the $\Lambda_{\mathrm{b}}^0 \to \mathrm{J}/\psi \Lambda \phi$ decay is reported using proton-proton collision data collected at $\sqrt{s} =$ 13 TeV by the CMS experiment at the LHC in 2018, corresponding to an integrated luminosity of 60 fb $^{-1}$ . The ratio of the branching fractions ${\cal B}(\Lambda_{\mathrm{b}}^0 \to \mathrm{J}/\psi \Lambda \phi)/{\cal B}(\Lambda_{\mathrm{b}}^0\to \psi{\mathrm{(2S)}} \Lambda)$ is measured to be (8.26 $\pm$ 0.90 (stat) $\pm$ 0.68 (syst) $\pm$ 0.11 ( ${\cal B}$ ) ) $\times 10^{-2}$ , where the first uncertainty is statistical, the second is systematic, and the last uncertainty reflects the uncertainties in the world-average branching fractions of $\phi$ and $\psi{\mathrm{(2S)}}$ decays to the reconstructed final states.
Links: e-print arXiv:1911.03789 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The invariant mass distributions of (left) ${\mathrm{J}/\psi} \Lambda {{\mathrm{K}} ^{+}} {{\mathrm{K}} ^{-}}$ and (right) background-subtracted ${{\mathrm{K}} ^{+}} {{\mathrm{K}} ^{-}}$ . The points are the data, with the vertical bars giving the statistical uncertainties, and the lines show the results of the fits described in the text.
png pdf	Figure 1-a: The invariant mass distribution of ${\mathrm{J}/\psi} \Lambda {{\mathrm{K}} ^{+}} {{\mathrm{K}} ^{-}}$ . The points are the data, with the vertical bars giving the statistical uncertainties, and the lines show the results of the fits described in the text.
png pdf	Figure 1-b: The invariant mass distribution of background-subtracted ${{\mathrm{K}} ^{+}} {{\mathrm{K}} ^{-}}$ . The points are the data, with the vertical bars giving the statistical uncertainties, and the lines show the results of the fits described in the text.
png pdf	Figure 2: The invariant mass distribution of $\Lambda _{\mathrm {b}}^0\to \psi{\mathrm{(2S)}}\Lambda$ candidates. The points are the data and the lines give the result of the fit described in the text.

Tables
png pdf	Table 1: Summary of the relative systematic uncertainties in ${\cal B}(\Lambda _{\mathrm {b}}^0\to {\mathrm{J}/\psi} \Lambda \phi)/{\cal B}(\Lambda _{\mathrm {b}}^0\to \psi{\mathrm{(2S)}}\Lambda)$ .

Summary

The observation of the

$\Lambda_{\mathrm{b}}^0 \to \mathrm{J}/\psi\Lambda \phi$ decay and the measurement of the branching fraction ratio

${\cal B}(\Lambda_{\mathrm{b}}^0 \to \mathrm{J}/\psi\Lambda \phi)/{\cal B}(\Lambda_{\mathrm{b}}^0 \to \psi{\mathrm{(2S)}} \Lambda)$ is presented using a data sample of proton-proton collisions at

$\sqrt{s} =$ 13 TeV collected in 2018 by the CMS experiment and corresponding to an integrated luminosity of 60 fb

$^{-1}$ . The ratio

${\cal B}(\Lambda_{\mathrm{b}}^0 \to \mathrm{J}/\psi\Lambda \phi)/{\cal B}(\Lambda_{\mathrm{b}}^0 \to \psi{\mathrm{(2S)}} \Lambda)$ is measured to be (8.26

$\pm$ 0.90 (stat)

$\pm$ 0.68 (syst)

$\pm$ 0.11 (

${\cal B}$ ) )

$\times 10^{-2}$ , where the first uncertainty is statistical, the second is systematic, and the last uncertainty reflects the uncertainties in the world-average branching fractions of

$\phi$ and

$\psi{\mathrm{(2S)}}$ decays to the reconstructed final states. The observation of the

$\Lambda_{\mathrm{b}}^0 \to \mathrm{J}/\psi\Lambda \phi$ decay opens a window on future searches for new resonances in the

$\mathrm{J}/\psi\Lambda$ and

$\mathrm{J}/\psi\phi$ mass spectra, once a sufficient number of signal events is observed.

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