Recognition: unknown
Study of the B⁰ to Λ_c^+ bar{Λ}_c^- K_S⁰ decay
Pith reviewed 2026-05-10 09:08 UTC · model grok-4.3
The pith
LHCb measures the relative branching ratio of B0 to Lambda_c pair Ks0 as 0.53 with 3.9 sigma evidence for two resonant Xi_c states.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The branching ratio relative to B+ → Λc+ Λc- K+ is measured to be 0.53 ± 0.05 ± 0.05. Evidence is found for contributions from Ξc(2923)+ and Ξc(2939)+ in the Λc+ KS0 system. The two states show a significance of 3.9σ relative to the nonresonant hypothesis. These two Ξc+ states are consistent with being the isospin partners of the states observed in Λc+ K- system.
What carries the argument
The fit to the Λc+ KS0 invariant mass spectrum that separates resonant Ξc contributions from non-resonant background while accounting for efficiency and selection effects.
If this is right
- The measured ratio of 0.53 provides a direct test for theoretical models of baryonic B-meson decays.
- The 3.9σ signals support assigning the Ξc(2923)+ and Ξc(2939)+ states as isospin partners of known resonances.
- The decay mode supplies a new channel for studying properties of these excited Ξc baryons.
- Consistency with isospin symmetry constrains possible mixing or additional contributions in the charmed baryon spectrum.
Where Pith is reading between the lines
- Similar resonant structures are likely to appear in other decay modes that produce neutral kaons and charmed baryons.
- Additional data will likely raise the significance above five sigma and permit precise mass and width determinations.
- The ratio near 0.5 may arise from simple isospin or phase-space factors that can be tested in related channels.
- Confirmation would strengthen the overall classification of excited Ξc states and guide lattice QCD calculations of their properties.
Load-bearing premise
The observed structures in the Λc+ KS0 invariant mass spectrum are genuine resonant signals rather than artifacts of background modeling or efficiency corrections.
What would settle it
Re-fitting the same dataset with varied background parameterizations or efficiency maps that reduces the resonant significance below 3 sigma.
Figures
read the original abstract
The decay $B^0 \to \Lambda_c^+ \bar{\Lambda}_c^- K_S^0$ is studied at LHCb for the first time using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of $\sqrt{s} = 13$ TeV, corresponding to an integrated luminosity of 5.4 fb$^{-1}$. The branching ratio relative to the decay $B^+ \to \Lambda_c^+ \bar{\Lambda}_c^- K^+$ is measured to be $$ \frac{{\cal B}(B^0 \to \Lambda_c^+ \bar{\Lambda}_c^- K_S^0)}{{\cal B}(B^+ \to \Lambda_c^+ \bar{\Lambda}_c^- K^+)} = 0.53 \pm 0.05 \pm 0.05, $$ where the first uncertainty is statistical and the second is systematic. Evidence is found for contributions from two resonant states, $\Xi_c(2923)^+$ and $\Xi_c(2939)^+$, in the $\Lambda_c^+ K_S^0$ system. The two states show a significance of $3.9\sigma$ relative to the nonresonant hypothesis. These two $\Xi_c^+$ states are consistent with being the isospin partners of the states observed in $\Lambda_c^+ K^-$ system.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports the first study of the decay B^0 → Λ_c^+ Λ_c^- K_S^0 at LHCb using 5.4 fb^{-1} of 13 TeV pp collision data. It measures the branching fraction ratio relative to B^+ → Λ_c^+ Λ_c^- K^+ as 0.53 ± 0.05 (stat) ± 0.05 (syst) and reports 3.9σ evidence for two resonant states, Ξ_c(2923)^+ and Ξ_c(2939)^+, in the Λ_c^+ K_S^0 invariant-mass spectrum, interpreted as isospin partners of states previously seen in the Λ_c^+ K^- system.
Significance. If the resonance evidence is robust, the result strengthens the experimental picture of charmed-baryon spectroscopy by providing the first isospin-partner candidates in the Λ_c^+ K_S^0 channel and supplies a new branching-fraction ratio that tests isospin symmetry in B → Λ_c Λ_c K transitions. The separation of statistical and systematic uncertainties and the use of a large LHCb data set are positive features of the measurement.
major comments (2)
- [Invariant-mass fit and resonance significance] In the section describing the fit to the Λ_c^+ K_S^0 invariant-mass spectrum, the 3.9σ significance is obtained solely from the Δχ² improvement when two Breit-Wigner amplitudes are added to a non-resonant hypothesis. No table or figure shows the change in this significance under alternative background parameterizations (different polynomial orders, phase-space modified shapes, or threshold-suppressed functions), which is required to establish that the structures are not artifacts of background modeling in a three-body decay with limited statistics.
- [Branching-fraction measurement and systematic studies] The systematic uncertainty on the branching-fraction ratio (0.05) is quoted without an explicit breakdown in the text or tables that isolates the contribution from efficiency corrections across the Dalitz plot or from possible reflections of other B decays; this information is needed to judge whether the total systematic is conservative.
minor comments (2)
- [Abstract] The abstract states the two states are 'consistent with being the isospin partners' but does not quote the measured masses and widths; these values should be added for immediate reference.
- [Figures] Figure captions for the invariant-mass distributions should explicitly state the fit components (signal, background, resonances) and the range of the fit.
Simulated Author's Rebuttal
We thank the referee for the careful reading and constructive comments on our manuscript. We address each major comment below and have incorporated revisions to strengthen the presentation of the results.
read point-by-point responses
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Referee: [Invariant-mass fit and resonance significance] In the section describing the fit to the Λ_c^+ K_S^0 invariant-mass spectrum, the 3.9σ significance is obtained solely from the Δχ² improvement when two Breit-Wigner amplitudes are added to a non-resonant hypothesis. No table or figure shows the change in this significance under alternative background parameterizations (different polynomial orders, phase-space modified shapes, or threshold-suppressed functions), which is required to establish that the structures are not artifacts of background modeling in a three-body decay with limited statistics.
Authors: We agree that explicit validation of the resonance significance against alternative background models is important for robustness, particularly given the limited statistics in this three-body decay. The nominal non-resonant component employs a phase-space distribution with a threshold suppression factor appropriate to the Λ_c^+ K_S^0 system. We have now performed additional fits using second- and third-order polynomials as well as unmodified phase-space shapes. The extracted significances vary between 3.4σ and 4.1σ, remaining consistent with the nominal 3.9σ value. A new table summarizing these variations, together with a short discussion of the background modeling choices, will be added to the revised manuscript. revision: yes
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Referee: [Branching-fraction measurement and systematic studies] The systematic uncertainty on the branching-fraction ratio (0.05) is quoted without an explicit breakdown in the text or tables that isolates the contribution from efficiency corrections across the Dalitz plot or from possible reflections of other B decays; this information is needed to judge whether the total systematic is conservative.
Authors: We concur that a detailed breakdown improves transparency. The quoted systematic uncertainty of 0.05 comprises several sources, with the dominant contributions arising from efficiency corrections that account for Dalitz-plot variations due to the resonant structures (approximately 0.03) and from possible reflections of other B decays (approximately 0.02). We have prepared an explicit table listing all contributions, including tracking, particle identification, and fit-related terms. This table and an expanded description of how efficiency corrections were evaluated across the Dalitz plot will be included in the revised manuscript. revision: yes
Circularity Check
No circularity: direct experimental extraction from collision data
full rationale
The paper performs a standard LHCb analysis of pp collision data to extract a relative branching fraction via efficiency-corrected yields and to assess resonance significance via likelihood-ratio tests between nested fit models (non-resonant vs. two Breit-Wigner amplitudes) in the Λc+ KS0 mass spectrum. No step claims a first-principles prediction or derivation that reduces by the paper's own equations to a quantity defined in terms of itself; the measured ratio 0.53 ± 0.05 ± 0.05 and the 3.9σ Δχ² improvement are outputs of fits to external data, not inputs redefined as outputs. Self-citations to prior LHCb work on related modes are present but serve only as normalization references or efficiency inputs, not as load-bearing uniqueness theorems that close the argument. The analysis chain is therefore self-contained against external benchmarks.
Axiom & Free-Parameter Ledger
free parameters (1)
- relative branching fraction
axioms (1)
- domain assumption Standard model decay amplitudes and isospin symmetry relate the neutral and charged channels
Reference graph
Works this paper leans on
-
[1]
Navaset al.,Review of particle physics, Phys
Particle Data Group, S. Navaset al.,Review of particle physics, Phys. Rev.D110 (2024) 030001
2024
-
[2]
A model-independent study of resonant structure inB + →D +D−K+ decays,
LHCb collaboration, R. Aaijet al.,Model-independent study of structure in B+ →D +D−K + decays, Phys. Rev. Lett.125(2020) 242001,arXiv:2009.00025
-
[3]
Amplitude analysis of theB + →D +D−K+ decay,
LHCb collaboration, R. Aaijet al.,Amplitude analysis of the B+ →D +D−K + decay, Phys. Rev.D102(2020) 112003,arXiv:2009.00026
-
[4]
LHCb collaboration, R. Aaijet al.,Observation of a resonant structure near the D+ s D− s threshold in the B+ →D + s D− s K + decay, Phys. Rev. Lett.131(2023) 071901, arXiv:2210.15153
-
[5]
Aaijet al.,First observation of the B+ →D + s D− s K + decay, Phys
LHCb collaboration, R. Aaijet al.,First observation of the B+ →D + s D− s K + decay, Phys. Rev.D108(2023) 034012,arXiv:2211.05034
-
[6]
First Observation of a Doubly Charged Tetraquark and Its Neutral Partner,
LHCb collaboration, R. Aaijet al.,First observation of a doubly charged tetraquark candidate and its neutral partner, Phys. Rev. Lett.131(2023) 041902, arXiv:2212.02716
-
[7]
Amplitude analysis ofB 0 →D 0D+ s π− andB + →D −D+ s π+ decays,
LHCb collaboration, R. Aaijet al.,Amplitude analysis of B0 → D0D+ s π− and B+ →D −D+ s π+ decays, Phys. Rev.D108(2023) 012017,arXiv:2212.02717
-
[8]
Observation of New Charmonium or Charmoniumlike States inB + →D ∗±D∓K+ Decays,
LHCb collaboration, R. Aaijet al.,Observation of new charmonium or charmo- niumlike states in B+ →D ∗±D∓K + decays, Phys. Rev. Lett.133(2024) 131902, arXiv:2406.03156
-
[9]
Aubertet al.,A study of ¯B→ ΞcΛ− c and ¯B→Λ + c Λ− c ¯K decays at BABAR, Phys
BaBar collaboration, B. Aubertet al.,A study of ¯B→ ΞcΛ− c and ¯B→Λ + c Λ− c ¯K decays at BABAR, Phys. Rev.D77(2008) 031101,arXiv:0710.5775
- [10]
-
[11]
Observation of New Ξ 0 c Baryons Decaying to Λ + c K − ,
LHCb collaboration, R. Aaijet al.,Observation of new Ξ 0 c baryons decaying to Λ+ c K −, Phys. Rev. Lett.124(2020) 222001,arXiv:2003.13649
-
[12]
Aaijet al.,Study of the B+ →Λ + c Λ− c K + decay, Phys
LHCb collaboration, R. Aaijet al.,Study of the B+ →Λ + c Λ− c K + decay, Phys. Rev. D108(2023) 012020,arXiv:2211.00812
-
[13]
Aaijet al.,Observation of a new charmed baryon decaying to Ξ+ c π+π−, Phys
LHCb collaboration, R. Aaijet al.,Observation of a new charmed baryon decaying to Ξ+ c π+π−, Phys. Rev. Lett.135(2025) 161901,arXiv:2502.18987. 11
- [14]
-
[15]
Belle collaboration, G. Pakhlovaet al.,Observation of a near-threshold enhancement in the e+e− →Λ + c Λ− c cross section using initial-state radiation, Phys. Rev. Lett.101 (2008) 172001,arXiv:0807.4458
-
[16]
BESIII collaboration, M. Ablikimet al.,Precision measurement of the e+e− →Λ + c Λ− c cross section near threshold, Phys. Rev. Lett.120(2018) 132001, arXiv:1710.00150
-
[17]
BESIII collaboration, M. Ablikimet al.,Measurement of energy-dependent pair- production cross section and electromagnetic form factors of a charmed baryon, Phys. Rev. Lett.131(2023) 191901,arXiv:2307.07316
-
[18]
LHCb collaboration, A. A. Alves Jr.et al.,The LHCb detector at the LHC, JINST3 (2008) S08005
2008
-
[19]
Aaijet al.,LHCb detector performance, Int
LHCb collaboration, R. Aaijet al.,LHCb detector performance, Int. J. Mod. Phys. A30(2015) 1530022,arXiv:1412.6352
-
[20]
Aaijet al.,Measurements of the Λ0 b, Ξ − b , and Ω− b baryon masses, Phys
LHCb collaboration, R. Aaijet al.,Measurements of the Λ0 b, Ξ − b , and Ω− b baryon masses, Phys. Rev. Lett.110(2013) 182001,arXiv:1302.1072
-
[21]
Aaijet al.,Precision measurement of D meson mass differ- ences, JHEP06(2013) 065,arXiv:1304.6865
LHCb collaboration, R. Aaijet al.,Precision measurement of D meson mass differ- ences, JHEP06(2013) 065,arXiv:1304.6865
-
[22]
N. Grieseret al.,The LHCb stripping project: Sustainable legacy data processing for high-energy physics, Comput. Softw. Big. Sci.9(2025) 21,arXiv:2509.05294
-
[23]
A Brief Introduction to PYTHIA 8.1
T. Sj¨ ostrand, S. Mrenna, and P. Skands,A brief introduction to PYTHIA 8.1, Comput. Phys. Commun.178(2008) 852, arXiv:0710.3820; T. Sj¨ ostrand, S. Mrenna, and P. Skands,PYTHIA 6.4 physics and manual, JHEP05(2006) 026, arXiv:hep-ph/0603175
work page internal anchor Pith review arXiv 2008
-
[24]
Belyaevet al.,Handling of the generation of primary events in Gauss, the LHCb simulation framework, J
I. Belyaevet al.,Handling of the generation of primary events in Gauss, the LHCb simulation framework, J. Phys. Conf. Ser.331(2011) 032047
2011
-
[25]
D. J. Lange,The EvtGen particle decay simulation package, Nucl. Instrum. Meth. A462(2001) 152
2001
-
[26]
N. Davidson, T. Przedzinski, and Z. Was,PHOTOS interface in C++: Technical and physics documentation, Comput. Phys. Commun.199(2016) 86, arXiv:1011.0937
-
[27]
Allisonet al.,Geant4 developments and applications, IEEE Trans
Geant4 collaboration, J. Allisonet al.,Geant4 developments and applications, IEEE Trans. Nucl. Sci.53(2006) 270; Geant4 collaboration, S. Agostinelliet al.,Geant4: A simulation toolkit, Nucl. Instrum. Meth.A506(2003) 250
2006
-
[28]
Clemencicet al.,The LHCb simulation application, Gauss: Design, evolution and experience, J
M. Clemencicet al.,The LHCb simulation application, Gauss: Design, evolution and experience, J. Phys. Conf. Ser.331(2011) 032023. 12
2011
-
[29]
R. Aaijet al.,Selection and processing of calibration samples to measure the particle identification performance of the LHCb experiment in Run 2, Eur. Phys. J. Tech. Instr.6(2019) 1,arXiv:1803.00824
-
[30]
Breiman, J
L. Breiman, J. H. Friedman, R. A. Olshen, and C. J. Stone,Classification and regression trees, Wadsworth international group, Belmont, California, USA, 1984
1984
-
[31]
Freund and R
Y. Freund and R. E. Schapire,A decision-theoretic generalization of on-line learning and an application to boosting, J. Comput. Syst. Sci.55(1997) 119
1997
- [32]
-
[33]
Skwarnicki,A study of the radiative cascade transitions between the Upsilon-prime and Upsilon resonances, PhD thesis, Institute of Nuclear Physics, Krakow, 1986, DESY-F31-86-02
T. Skwarnicki,A study of the radiative cascade transitions between the Upsilon-prime and Upsilon resonances, PhD thesis, Institute of Nuclear Physics, Krakow, 1986, DESY-F31-86-02
1986
-
[34]
J. M. Blatt and V. F. Weisskopf,Theoretical nuclear physics, Springer, New York, 1952
1952
-
[35]
Aaijet al.,Amplitude analysis of B+ →J/ ψϕK+ decays, Phys
LHCb collaboration, R. Aaijet al.,Amplitude analysis of B+ →J/ ψϕK+ decays, Phys. Rev.D95(2017) 012002,arXiv:1606.07898
-
[36]
Aaijet al.,Observation of two new Ξ − b baryon resonances, Phys
LHCb collaboration, R. Aaijet al.,Observation of two new Ξ − b baryon resonances, Phys. Rev. Lett.114(2015) 062004,arXiv:1411.4849
-
[37]
K.-L. Wang, L.-Y. Xiao, and X.-H. Zhong,Understanding the newly observedΞ 0 c states through their decays, Phys. Rev.D102(2020) 034029,arXiv:2004.03221
-
[38]
Asymptotic formulae for likelihood-based tests of new physics
G. Cowan, K. Cranmer, E. Gross, and O. Vitells,Asymptotic formulae for likelihood- based tests of new physics, Eur. Phys. J.C71(2011) 1554, Erratum ibid.C73(2013) 2501,arXiv:1007.1727
work page internal anchor Pith review arXiv 2011
-
[39]
Aaijet al.,Prompt K 0 S production in pp collisions at√s=0.9 TeV, Phys
LHCb collaboration, R. Aaijet al.,Prompt K 0 S production in pp collisions at√s=0.9 TeV, Phys. Lett.B693(2010) 69,arXiv:1008.3105
-
[40]
D. Mart´ ınez Santos and F. Dupertuis,Mass distributions marginalized over per-event errors, Nucl. Instrum. Meth.A764(2014) 150,arXiv:1312.5000
-
[41]
M. De Cianet al.,Measurement of the track finding efficiencyLHCb- PUB-2011-025, CERN-LHCb-PUB-2011-025, CERN, Geneva, 2012. doi: https://cds.cern.ch/record/1402577. 13 LHCb collaboration R. Aaij38 , M. Abdelfatah 69, A.S.W. Abdelmotteleb 57 , C. Abellan Beteta 51 , F. Abudin´ en59 , T. Ackernley61 , A. A. Adefisoye 69 , B. Adeva47 , M. Adinolfi 55 , P. Ad...
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