CMS-BPH-22-002

CMS-BPH-22-002 ; CERN-EP-2024-006
Observation of the $ \Lambda_{b}^{0}\to\mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ decay
CMS Collaboration
29 January 2024
Submitted to Eur. Phys. J. C
Abstract: Using proton-proton collision data corresponding to an integrated luminosity of 140 fb$ ^{-1} $ collected by the CMS experiment at $ \sqrt{s}= $ 13 TeV, the $ \Lambda_{b}^{0}\to\mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ decay is observed for the first time, with a statistical significance exceeding 5 standard deviations. The relative branching fraction, with respect to the $ \Lambda_{b}^{0}\to\psi(2\mathrm{S})\Lambda $ decay, is measured to be $ \mathcal{B}(\Lambda_{b}^{0}\to\mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+})/\mathcal{B}(\Lambda_{b}^{0}\to\psi(2\mathrm{S})\Lambda) = [ $ 3.38 $ \pm $ 1.02 $ \pm $ 0.61 $ \pm $ 0.03 $ ]$%, where the first uncertainty is statistical, the second is systematic, and the third is related to the uncertainties in $ \mathcal{B}(\psi(2\mathrm{S})\to\mathrm{J}/\psi\,\pi^{+}\pi^{-}) $ and $ \mathcal{B}(\Xi^{-}\to\Lambda\pi^{-}) $.
Links: e-print arXiv:2401.16303 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Measured $ \psi(2\mathrm{S})\Lambda $ (left) and $ \mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ (right) invariant mass distributions and overlaid fit results.
png pdf	Figure 1-a: Measured $ \psi(2\mathrm{S})\Lambda $ invariant mass distribution and overlaid fit result.
png pdf	Figure 1-b: Measured $ \mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ invariant mass distribution and overlaid fit result.
png pdf	Figure 2: Intermediate invariant mass distributions of the $ \Lambda_{b}^{0}\to\mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ decay. The filled circles and empty squares show the measured background-subtracted distributions and the results from the simulation with a phase-space model, respectively.
png pdf	Figure 2-a: $ \mathrm{J}/\psi\,\mathrm{K^+} $ invariant mass distribution. The filled circles and empty squares show the measured background-subtracted distribution and the results from the simulation with a phase-space model, respectively.
png pdf	Figure 2-b: $ \Xi^{-}\mathrm{K^+} $ invariant mass distribution. The filled circles and empty squares show the measured background-subtracted distribution and the results from the simulation with a phase-space model, respectively.
png pdf	Figure 2-c: $ \mathrm{J}/\psi\,\mathrm{K^+} $ invariant mass distribution. The filled circles and empty squares show the measured background-subtracted distribution and the results from the simulation with a phase-space model, respectively.
png pdf	Figure 3: Measured $ \psi(2\mathrm{S})\Lambda $ (left) and $ \mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ (right) invariant mass distributions and corresponding fits used for the measurement of $ \mathcal{R} $.
png pdf	Figure 3-a: Measured $ \psi(2\mathrm{S})\Lambda $ invariant mass distribution and corresponding fit used for the measurement of $ \mathcal{R} $.
png pdf	Figure 3-b: Measured $ \mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ invariant mass distribution and corresponding fit used for the measurement of $ \mathcal{R} $.
png pdf	Figure 4: Measured $ \mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ invariant mass distribution and overlaid constrained fit result.

Tables
png pdf	Table 1: Optimized selection criteria for the signal decay mode $ \Lambda_{b}^{0}\to\mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $. The first two requirements are applied using the momenta before the corresponding mass constraint.
png pdf	Table 2: The relative systematic uncertainties in the measurement of $ \mathcal{R} $.

Summary

The $ \Lambda_{b}^{0}\to\mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ decay is observed with a significance exceeding 5 standard deviations using $ \sqrt{s}= $ 13 TeV proton-proton collision data corresponding to an integrated luminosity of 140 fb$^{-1}$ collected by the CMS experiment. The branching fraction is measured with respect to the $ \Lambda_{b}^{0}\to\psi(2\mathrm{S})\Lambda $ decay to be $ \mathcal{B}(\Lambda_{b}^{0}\to\mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+})/\mathcal{B}(\Lambda_{b}^{0}\to\psi(2\mathrm{S})\Lambda) = [ $ 3.38 $ \pm $ 1.02 (stat) $ \pm $ 0.61 (syst) $ \pm 0.03\,(\mathcal{B})]$%. The distributions of intermediate invariant masses $ m(\mathrm{J}/\psi\,\Xi^{-}) $, $ m(\mathrm{J}/\psi\,\mathrm{K^+}) $, and $ m(\Xi^{-}\mathrm{K^+}) $ from the $ \Lambda_{b}^{0}\to\mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ decay are also presented. This is the first discovered multibody decay containing the $ \mathrm{J}/\psi\,\Xi^{-} $ system, which opens the possibility to search for doubly-strange hidden-charm pentaquarks when more data are collected. The new results are important for understanding the strong interaction processes in hadronic decays of beauty baryons and the possible formation of exotic multiquark states.

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