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CMS-BPH-22-002 ; CERN-EP-2024-006
Observation of the $ \Lambda_{b}^{0}\to\mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ decay
Accepted for publication in 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^{-}) $.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
Measured $ \psi(2\mathrm{S})\Lambda $ (left) and $ \mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ (right) invariant mass distributions and overlaid fit results.

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Figure 1-a:
Measured $ \psi(2\mathrm{S})\Lambda $ invariant mass distribution and overlaid fit result.

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Figure 1-b:
Measured $ \mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ invariant mass distribution and overlaid fit result.

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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.

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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.

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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.

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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.

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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} $.

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Figure 3-a:
Measured $ \psi(2\mathrm{S})\Lambda $ invariant mass distribution and corresponding fit used for the measurement of $ \mathcal{R} $.

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Figure 3-b:
Measured $ \mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ invariant mass distribution and corresponding fit used for the measurement of $ \mathcal{R} $.

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Figure 4:
Measured $ \mathrm{J}/\psi\,\Xi^{-}\mathrm{K^+} $ invariant mass distribution and overlaid constrained fit result.
Tables

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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.

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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.
References
1 LHCb Collaboration Observation of $ \mathrm{J}/\psi \mathrm{p} $ resonances consistent with pentaquark states in $ \Lambda_{b}^{0}\to\mathrm{J}/\psi\mathrm{p}\mathrm{K^-} $ decays PRL 115 (2015) 072001 1507.03414
2 L. Maiani, A. D. Polosa, and V. Riquer The new pentaquarks in the diquark model PLB 749 (2015) 289 1507.04980
3 E. Santopinto and A. Giachino Compact pentaquark structures PRD 96 (2017) 014014 1604.03769
4 L. Roca, J. Nieves, and E. Oset LHCb pentaquark as a $ \bar{D}^*\Sigma_c-\bar{D}^*\Sigma_c^* $ molecular state PRD 92 (2015) 094003 1507.04249
5 M. I. Eides, V. Y. Petrov, and M. V. Polyakov Pentaquarks with hidden charm as hadroquarkonia EPJC 78 (2018) 36 1709.09523
6 M.-L. Du et al. Interpretation of the LHCb $ P_c $ states as hadronic molecules and hints of a narrow $ P_c(4380) $ PRL 124 (2020) 072001 1910.11846
7 S. X. Nakamura $ P_c(4312)^+ $, $ P_c(4380)^+ $, and $ P_c(4457)^+ $ as double triangle cusps PRD 103 (2021) 111503 2103.06817
8 LHCb Collaboration Observation of a narrow pentaquark state, $ P_c(4312)^+ $, and of two-peak structure of the $ P_c(4450)^+ $ PRL 122 (2019) 222001 1904.03947
9 LHCb Collaboration Evidence of a $ \mathrm{J}/\psi\Lambda $ structure and observation of excited $ \Xi^{-} $ states in the $ \Xi_{b}^{-} \to \mathrm{J}/\psi\Lambda \mathrm{K^-} $ decay Sci. Bull. 66 (2021) 1278 2012.10380
10 LHCb Collaboration Evidence for a new structure in the $ \mathrm{J}/\psi\mathrm{p} $ and $ \mathrm{J}/\psi\overline{\mathrm{p}} $ systems in $ \mathrm{B}_{s}^{0}\to\mathrm{J}/\psi\mathrm{p}\overline{\mathrm{p}} $ decays PRL 128 (2022) 062001 2108.04720
11 LHCb Collaboration Observation of a $ \mathrm{J}/\psi\Lambda $ resonance consistent with a strange pentaquark candidate in $ {\mathrm{B}^{-}}\to \mathrm{J}/\psi\Lambda\bar{p} $ decays PRL 131 (2023) 031901 2210.10346
12 K. Azizi, Y. Sarac, and H. Sundu Investigation of hidden-charm double strange pentaquark candidate $ P_{css} $ via its mass and strong decays EPJC 82 (2022) 543 2112.15543
13 F.-L. Wang, X.-D. Yang, R. Chen, and X. Liu Hidden-charm pentaquarks with triple strangeness due to the $ \Omega_{c}^{(*)}\bar{D}_s^{(*)} $ interactions PRD 103 (2021) 054025 2101.11200
14 CMS Collaboration Precision luminosity measurement in proton-proton collisions at $ \sqrt{s} = $ 13 TeV in 2015 and 2016 at CMS EPJC 81 (2021) 800 CMS-LUM-17-003
2104.01927
15 CMS Collaboration CMS luminosity measurement for the 2017 data-taking period at $ \sqrt{s} = $ 13 TeV CMS Physics Analysis Summary, 2018
CMS-PAS-LUM-17-004
CMS-PAS-LUM-17-004
16 CMS Collaboration CMS luminosity measurement for the 2018 data-taking period at $ \sqrt{s} = $ 13 TeV CMS Physics Analysis Summary, 2019
CMS-PAS-LUM-18-002
CMS-PAS-LUM-18-002
17 CMS Collaboration HEPData record for this analysis link
18 CMS Collaboration The CMS experiment at the CERN LHC JINST 3 (2008) S08004
19 CMS Collaboration Description and performance of track and primary-vertex reconstruction with the CMS tracker JINST 9 (2014) P10009 CMS-TRK-11-001
1405.6569
20 CMS Tracker Collaboration The CMS Phase-1 pixel detector upgrade JINST 16 (2021) P02027 2012.14304
21 CMS Collaboration Track impact parameter resolution for the full pseudo rapidity coverage in the 2017 dataset with the CMS Phase-1 pixel detector CMS Detector Performance Note CMS-DP-2020-049, 2020
CDS
22 CMS Collaboration The CMS trigger system JINST 12 (2017) P01020 CMS-TRG-12-001
1609.02366
23 CMS Collaboration Performance of the CMS Level-1 trigger in proton-proton collisions at $ \sqrt{s} = $ 13\,TeV JINST 15 (2020) P10017 CMS-TRG-17-001
2006.10165
24 T. Sjöstrand et al. An introduction to PYTHIA 8.2 Comput. Phys. Commun. 191 (2015) 159 1410.3012
25 CMS Collaboration Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements EPJC 80 (2020) 4 CMS-GEN-17-001
1903.12179
26 D. J. Lange The EvtGen particle decay simulation package NIM A 462 (2001) 152
27 E. Barberio and Z. Was PHOTOS --- a universal Monte Carlo for QED radiative corrections: version 2.0 Comput. Phys. Commun. 79 (1994) 291
28 GEANT4 Collaboration GEANT 4 --- a simulation toolkit NIM A 506 (2003) 250
29 CMS Collaboration Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $ \sqrt{s}= $ 13 TeV JINST 13 (2018) P06015 CMS-MUO-16-001
1804.04528
30 CMS Collaboration CMS tracking performance results from early LHC operation EPJC 70 (2010) 1165 CMS-TRK-10-001
1007.1988
31 Particle Data Group Collaboration Review of particle physics Prog. Theor. Exp. Phys. 2022 (2022) 083C01
32 G. Punzi Sensitivity of searches for new signals and its optimization in Proceedings of PHYSTAT 2003, Statistical problems in particle physics, astrophysics and cosmology physics/0308063
33 S. Jackman Bayesian analysis for the social sciences John Wiley & Sons, New Jersey, USA, 2009
link
34 S. S. Wilks The large-sample distribution of the likelihood ratio for testing composite hypotheses Annals Math. Statist. 9 (1938) 60
35 G. Cowan, K. Cranmer, E. Gross, and O. Vitells Asymptotic formulae for likelihood-based tests of new physics EPJC 71 (2011) 1554 1007.1727
36 N. L. Johnson Systems of frequency curves generated by methods of translation Biometrika 36 (1949) 149
37 M. Pivk and F. R. Le Diberder $ _\mathrm{{s}}\mathcal{P}\mathrm{lot} $: a statistical tool to unfold data distributions NIM A 555 (2005) 356 physics/0402083
38 CMS Collaboration Tracking performances for charged pions with Run2 legacy data CMS Detector Performance Note CMS-DP-2022-012, 2022
CDS
39 CMS Collaboration Observation of a new excited beauty strange baryon decaying to $ \Xi_{b}^{-}\pi^{+}\pi^{-} $ PRL 126 (2021) 252003 CMS-BPH-20-004
2102.04524
40 CMS Collaboration Study of excited $ \Lambda_\mathrm{b}^0 $ states decaying to $ \Lambda_\mathrm{b}^0\pi^+\pi^- $ in proton-proton collisions at $ \sqrt{s}= $ 13 TeV PLB 803 (2020) 135345 CMS-BPH-19-003
2001.06533
Compact Muon Solenoid
LHC, CERN