CMS-PAS-BPH-19-002

CMS-PAS-BPH-19-002
Observation of the $\Lambda_{\mathrm{b}} \to \mathrm{J}/\psi \Lambda \phi$ decay in proton-proton collisions at $\sqrt{s}=$ 13 TeV
CMS Collaboration
August 2019

Abstract: We report a first observation of the $\Lambda_{\mathrm{b}} \to \mathrm{J}/\psi \Lambda \phi$ decay using proton-proton collision data collected at $\sqrt{s}$ = 13 TeV by the CMS experiment at the LHC, and corresponding to an integrated luminosity of 60 fb $^{-1}$ . The ratio of the branching fractions ${\cal B}(\Lambda_{\mathrm{b}} \to \mathrm{J}/\psi \Lambda \phi)/{\cal B}(\Lambda_{\mathrm{b}}\to \psi\mathrm{(2S)} \Lambda)$ 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 third is due to the uncertainties in the world-average branching fractions.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, PLB 802 (2020) 135203. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The invariant mass distribution $M({\mathrm{J}/\psi} \Lambda {{\mathrm{K}} ^{+}} {{\mathrm{K}} ^{-}})$ (left) and the background-subtracted distribution of $M({{\mathrm{K}} ^{+}} {{\mathrm{K}} ^{-}})$ (right). The choice of the fit function is explained in the text.
png pdf	Figure 1-a: The invariant mass distribution $M({\mathrm{J}/\psi} \Lambda {{\mathrm{K}} ^{+}} {{\mathrm{K}} ^{-}})$ (left) and the background-subtracted distribution of $M({{\mathrm{K}} ^{+}} {{\mathrm{K}} ^{-}})$ (right). The choice of the fit function is explained in the text.
png pdf	Figure 1-b: The invariant mass distribution $M({\mathrm{J}/\psi} \Lambda {{\mathrm{K}} ^{+}} {{\mathrm{K}} ^{-}})$ (left) and the background-subtracted distribution of $M({{\mathrm{K}} ^{+}} {{\mathrm{K}} ^{-}})$ (right). The choice of the fit function is explained in the text.
png pdf	Figure 2: The invariant mass distribution of $\Lambda_{\mathrm{b}} \to \psi\mathrm{(2S)}\Lambda$ candidates. The points are data and the curve is the result of the fit described in the text.

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

Summary

We report the first observation of the

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

${\cal B}(\Lambda_{\mathrm{b}} \to \mathrm{J}/\psi\Lambda \phi)/{\cal B}(\Lambda_{\mathrm{b}} \to \psi\mathrm{(2S)} \Lambda)$ using a data sample of pp collisions at

$\sqrt{s} =$ 13 TeV recorded in 2018 and corresponding to an integrated luminosity of 60 fb

$^{-1}$ . The branching fraction ratio

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

$\pm$ 0.90 (stat)

$\pm$ 0.68 (syst)

$\pm$ 0.11 (

${\cal B}$ ) )

$\times 10^{-2}$ .

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