Evidence of a new excited charmed baryon at Belle

A charmed baryon is a kind of baryon containing at least one charm quark. There exist abundant excited charmed baryons, and the study of charmed baryon spectroscopy is very important for understanding the dynamics of light quarks in the environment of a heavy quark, and for testing heavy-quark symmetry and the chiral symmetry of light quarks. The Λ⁺_c baryon is the lightest charmed baryon, which is an isospin singlet composed of one charm quark, one up quark and one down quark. Very recently, using a data sample of 770 million BB events collected at Υ(4S) resonance in the Belle experiment, Japan, studies were performed on the decay B⁰ → Σ_c (2455)^{0, ++}π^±p. A new structure has been found in the invariant mass distribution of Σ_c (2455)^{0, ++}π^± with a significance of 4.2σ including systematic uncertainty, which means that the probability of the emergence of this structure due to statistical fluctuation and various uncertainties is less than 0.002%. Its mass and width are measured to be (2913.8 ± 5.6 ± 3.8) MeV/c² and (51.8 ± 20.0 ± 18.8) MeV, respectively. No known excited charmed baryon can match the observed new structure. It is probably a new excited Λ_c baryon, tentatively named as Λ_c (2910)⁺.