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Observation and Measurement of Ξ⁻ᵇ and Ω⁻ᵇ Baryon Decays to Λ⁺ₓ h⁻ h'⁻ Final States


Core Concepts
Decays of Ξ⁻ᵇ and Ω⁻ᵇ baryons to Λ⁺ₓ h⁻ h'⁻ final states, with h⁻ h'⁻ being π⁻ π⁻, K⁻ π⁻ and K⁻ K⁻ meson pairs, are observed and their branching fractions measured relative to the B⁻ → Λ⁺ₓ pπ⁻ mode. The Ξ⁻ᵇ production asymmetry is also measured.
Abstract

This analysis searches for decays of Ξ⁻ᵇ and Ω⁻ᵇ baryons to Λ⁺ₓ h⁻ h'⁻ final states, where h⁻ and h'⁻ are K⁻ or π⁻ mesons. The data sample corresponds to an integrated luminosity of 8.7 fb⁻¹ of pp collisions collected with the LHCb detector.

Key highlights:

  • Ξ⁻ᵇ → Λ⁺ₓ K⁻ π⁻, Ξ⁻ᵇ → Λ⁺ₓ K⁻ K⁻ and Ω⁻ᵇ → Λ⁺ₓ K⁻ K⁻ decays are observed with over 5σ significance.
  • The product of the relative branching fractions and fragmentation fractions for each signal mode are measured, using the B⁻ → Λ⁺ₓ pπ⁻ mode as a control channel.
  • The Ξ⁻ᵇ production asymmetry is measured and found to be consistent with zero.
  • The previously unobserved B⁻ → Λ⁺ₓ pK⁻ decay is also observed and its branching fraction measured relative to B⁻ → Λ⁺ₓ pπ⁻.

The analysis uses a blind approach for the Ξ⁻ᵇ and Ω⁻ᵇ baryon decays, with the signal mass regions not inspected until the analysis procedures are established. Efficiency corrections accounting for detector effects and phase-space distributions are applied, and various systematic uncertainties are evaluated.

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Stats
The Ξ⁻ᵇ → Λ⁺ₓ K⁻ π⁻ mode is used to measure the Ξ⁻ᵇ production asymmetry, which is found to be consistent with zero. The B⁻ → Λ⁺ₓ pK⁻ decay is observed for the first time.
Quotes
"Decays of Ξ⁻ᵇ and Ω⁻ᵇ baryons to Λ⁺ₓ h⁻ h'⁻ final states, with h⁻ h'⁻ being π⁻ π⁻, K⁻ π⁻ and K⁻ K⁻ meson pairs, are searched for using data collected with the LHCb detector." "The Ξ⁻ᵇ → Λ⁺ₓ K⁻ π⁻ mode is also used to measure the Ξ⁻ᵇ production asymmetry, which is found to be consistent with zero." "The B⁻ → Λ⁺ₓ pK⁻ decay is observed for the first time, and its branching fraction is measured relative to that of the B⁻ → Λ⁺ₓ pπ⁻ mode."

Deeper Inquiries

How do the measured production asymmetries and branching fractions of the Ξ⁻ᵇ and Ω⁻ᵇ baryons compare to theoretical predictions from QCD models?

The measured production asymmetries and branching fractions of the Ξ⁻ᵇ and Ω⁻ᵇ baryons provide critical insights into the validity of Quantum Chromodynamics (QCD) models. The results from the LHCb collaboration indicate that the production asymmetry for the Ξ⁻ᵇ baryon is consistent with zero, which aligns with theoretical expectations that suggest minimal asymmetry in the production of b-baryons due to the nature of strong interactions. The branching fractions measured for the decays of Ξ⁻ᵇ and Ω⁻ᵇ baryons to Λ⁺ₐ h⁻h'⁻ final states, particularly the significant observations of Ξ⁻ᵇ → Λ⁺ₐ K⁻π⁻ and Ω⁻ᵇ → Λ⁺ₐ K⁻K⁻, are also in line with theoretical predictions that account for Cabibbo-favored and Cabibbo-suppressed processes. These measurements help refine QCD models by providing empirical data that can constrain theoretical parameters, thereby enhancing our understanding of b-baryon production mechanisms and decay dynamics.

What are the implications of the observed Ξ⁻ᵇ and Ω⁻ᵇ decays for the spectroscopy of charm baryons, and could they provide evidence for exotic hadrons?

The observed decays of Ξ⁻ᵇ and Ω⁻ᵇ baryons to Λ⁺ₐ h⁻h'⁻ final states have significant implications for the spectroscopy of charm baryons. These decays allow for the exploration of the phase-space distribution of the final states, which can provide insights into the internal structure and interactions of charm baryons. The presence of specific decay modes, particularly those that are Cabibbo-suppressed, may hint at the existence of resonances or exotic hadrons that are not accounted for in conventional quark models. For instance, the decay patterns and branching fractions could suggest the presence of states that exhibit unusual quantum numbers or configurations, potentially leading to the discovery of exotic hadrons such as pentaquarks or tetraquarks. Thus, the study of these decays not only enriches our understanding of charm baryon spectroscopy but also opens avenues for investigating new and exotic forms of matter.

How could the techniques used in this analysis be extended to study other rare or previously unobserved b-baryon decays at the LHC?

The techniques employed in the analysis of Ξ⁻ᵇ and Ω⁻ᵇ decays can be effectively extended to investigate other rare or previously unobserved b-baryon decays at the LHC. Key methodologies include the use of advanced multivariate algorithms, such as boosted decision trees (BDTs), to enhance signal discrimination from background processes. This approach can be adapted to different decay channels by optimizing the selection criteria based on the specific kinematic and particle identification (PID) characteristics of the target decays. Additionally, the simultaneous unbinned extended maximum-likelihood fitting technique used to extract signal yields can be applied to other decay modes, allowing for the simultaneous analysis of multiple channels and the incorporation of cross-feed background contributions. Furthermore, the systematic uncertainties associated with efficiency corrections and phase-space distributions can be systematically evaluated and minimized, ensuring robust results. By leveraging these techniques, researchers can explore a broader spectrum of b-baryon decays, potentially uncovering new physics and enhancing our understanding of the b-quark sector.
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