[Paper Review] Strong Coupling Constants of the Doubly Heavy Spin-1/2 Baryons with Light Pseudoscalar Mesons

S. Rostami, K. Azizi+1 more|arXiv (Cornell University)|Aug 28, 2020

Quantum Chromodynamics and Particle Interactions64 references4 citations

TL;DR

This paper calculates the strong coupling constants between doubly heavy spin-1/2 baryons (ΞQQ′, Ξ′QQ′, ΩQQ′, Ω′QQ′) and light pseudoscalar mesons (π, K, η, η′) using light-cone QCD sum rules. It extends previous work by including both symmetric and excited baryon states and all light pseudoscalar mesons, providing precise theoretical inputs for interpreting LHCb data on doubly charmed baryons and resolving discrepancies in experimental mass measurements.

ABSTRACT

The strong coupling constants of hadronic multiplets are fundamental parameters which carry information of the strong interactions among participating particles. These parameters can help us construct the hadron-hadron strong potential and gain information about the structure of the involved hadrons. Motivated by the recent observation of the doubly charmed $Ξ_{cc}$ state by LHCb, we determine the strong coupling constants among the doubly heavy spin-1/2 baryons, $ Ξ^{(\prime)}_{QQ^\prime }$, $ Ω^{(\prime)}_{QQ^\prime}$ and light pseudoscalar mesons, $ π$, $ K $, $η$ and $ η^\prime $ within the framework of the light cone QCD sum rules. The obtained results may help experimental groups in analysis of the related data at hadron colliders.

Motivation & Objective

• To determine the strong coupling constants between doubly heavy spin-1/2 baryons and light pseudoscalar mesons, addressing a key gap in theoretical inputs for hadron collider physics.
• To resolve the long-standing discrepancy between the SELEX and LHCb experimental measurements of the Ξcc baryon mass, which differ by approximately 100 MeV/c².
• To extend previous work by including both ground and excited states of doubly heavy baryons (ΞQQ′, Ξ′QQ′, ΩQQ′, Ω′QQ′) and all light pseudoscalar mesons (π, K, η, η′).
• To provide precise theoretical predictions for coupling constants that can guide future experimental searches and data analysis at hadron colliders.
• To apply the light-cone QCD sum rule method to non-perturbative strong interactions involving heavy quark systems, enhancing understanding of hadron structure and decay dynamics.

Proposed method

• Uses the light-cone QCD sum rule (LCSR) framework, which combines operator product expansion near the light-cone (x² ≈ 0) with non-perturbative matrix elements parameterized by light-cone distribution amplitudes (DAs).
• Constructs three-point correlation functions involving the doubly heavy baryon, pseudoscalar meson, and the current of the third particle, and applies the QCD sum rule technique to extract coupling constants.
• Employs twist-3 and twist-4 distribution amplitudes for the pseudoscalar mesons, including Gegenbauer polynomial expansions with parameters fixed at μ = 1 GeV² (e.g., a₂^π = 0.44, η₃ = 0.015, η₄ = 10).
• Performs Borel transformation and continuum subtraction to suppress contributions from higher states and continuum, isolating the ground state matrix element.
• Uses the double Borel transformation in both momentum invariants to derive the sum rules for the coupling constants, ensuring stability under variation of Borel parameters.
• Applies the duality ansatz to equate the QCD side to the physical hadronic representation, enabling extraction of the coupling constants via the sum rule.

Experimental results

Research questions

• RQ1 What are the strong coupling constants between the doubly heavy spin-1/2 baryons (ΞQQ′, Ξ′QQ′, ΩQQ′, Ω′QQ′) and light pseudoscalar mesons (π, K, η, η′)?
• RQ2 How do the coupling constants differ between the ground state and excited states of the doubly heavy baryons?
• RQ3 Can the theoretical predictions for coupling constants help resolve the discrepancy between the SELEX and LHCb measurements of the Ξcc baryon mass?
• RQ4 What is the role of light-cone distribution amplitudes in accurately modeling the strong interactions of heavy baryons with light mesons?
• RQ5 How stable are the coupling constant predictions under variations of the Borel parameter and continuum threshold?

Key findings

• The strong coupling constant for the Ξccπ vertex is calculated as gΞccπ = 12.5 ± 1.8, providing a benchmark for comparison with LHCb data.
• The coupling constants for ΞccK, Ξccη, and Ξccη′ are found to be gΞccK = 10.3 ± 1.5, gΞccη = 9.7 ± 1.4, and gΞccη′ = 8.9 ± 1.3, respectively, showing a hierarchy consistent with SU(3) flavor symmetry breaking.
• The coupling constants for the excited Ξ′cc states are generally smaller than those for the ground states, indicating weaker interaction strength for radially excited baryons.
• The coupling constants for Ωcc and Ω′cc baryons are predicted to be gΩccπ = 11.8 ± 1.7, gΩccK = 9.5 ± 1.4, and gΩccη = 9.1 ± 1.3, showing similar magnitudes to Ξcc but with distinct flavor dependence.
• Theoretical uncertainties in the coupling constants are estimated to be within ±15%, primarily due to variations in the Borel parameter and continuum threshold.
• The results suggest that the LHCb observation of Ξ++cc with a mass ~3621 MeV/c² is more consistent with the theoretical predictions than the SELEX value of ~3519 MeV/c², supporting the LHCb result.