arXiv2025
Over the past few decades, the study of singly heavy baryons has entered a golden era, with numerous excited states observed by experimental collaborations. Various theoretical approaches have been developed to investigate their properties, with the QCD sum rule method being one of the most widely applied. This paper provides a review of these QCD sum rule studies. Over the last ten years, we have systematically studied $P$-wave singly heavy baryons using QCD sum rules and light-cone sum rules within the framework of heavy quark effective theory. These $P$-wave singly heavy baryons can explain many excited heavy baryons, including the $Λ_c(2595)^+$, $Λ_c(2625)^+$, $Ξ_c(2790)^{0/+}$, $Ξ_c(2815)^{0/+}$, $Σ_c(2800)^0$, $Ξ_c(2882)^0$, $Ξ_c(2923)^0$, $Ξ_c(2939)^0$, $Ξ_c(2965)^0$, $Ω_c(3000)^0$, $Ω_c(3066)^0$, $Ω_c(3090)^0$, $Ω_c(3050)^0$, $Ω_c(3119)^0$, $Λ_b(5912)^0$, $Λ_b(5920)^0$, $Ξ_b(6087)^0$, $Ξ_b(6095)^0/Ξ_b(6100)^-$, $Σ_b(6097)^\pm$, $Ξ_b(6227)^-$, $Ω_b(6316)^-$, $Ω_b(6330)^-$, $Ω_b(6340)^-$, and $Ω_b(6350)^-$, etc. Furthermore, we predict additional $P$-wave singly heavy baryons, including two $Λ_b$ states, two $Ξ_b$ states, three $Σ_b$ states, three $Ξ_b^\prime$ states, two $Ω_b$ states, two $Λ_c$ states, two $Ξ_c$ states, three $Σ_c$ states, and one $Ω_c$ state, all with relatively narrow decay widths, making them viable candidates for experimental observation. The study of singly heavy baryons is closely related to two meaningful questions:"What is the shortest possible lifetime of an observable particle?" and "How can one generally describe approximate (flavor) symmetries?".