A short review on QCD sum rule studies of P-wave single heavy baryons

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 $\Lambda_c(2595)^+$, $\Lambda_c(2625)^+$, $\Xi_c(2790)^{0/+}$, $\Xi_c(2815)^{0/+}$, $\Sigma_c(2800)^0$, $\Xi_c(2882)^0$, $\Xi_c(2923)^0$, $\Xi_c(2939)^0$, $\Xi_c(2965)^0$, $\Omega_c(3000)^0$, $\Omega_c(3066)^0$, $\Omega_c(3090)^0$, $\Omega_c(3050)^0$, $\Omega_c(3119)^0$, $\Lambda_b(5912)^0$, $\Lambda_b(5920)^0$, $\Xi_b(6087)^0$, $\Xi_b(6095)^0/\Xi_b(6100)^-$, $\Sigma_b(6097)^\pm$, $\Xi_b(6227)^-$, $\Omega_b(6316)^-$, $\Omega_b(6330)^-$, $\Omega_b(6340)^-$, and $\Omega_b(6350)^-$, etc. Furthermore, we predict additional $P$-wave singly heavy baryons, including two $\Lambda_b$ states, two $\Xi_b$ states, three $\Sigma_b$ states, three $\Xi_b^\prime$ states, two $\Omega_b$ states, two $\Lambda_c$ states, two $\Xi_c$ states, three $\Sigma_c$ states, and one $\Omega_c$ 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?".