Recent experimental results on charmed baryons

BABAR has recently published a study of the decay B → Λ+c p̄π in a sample of 383 × 10 Υ(4S) → BB decays [7, 3] measuring B(B− → Λ+c p̄π) = (3.38 ± 0.12 ± 0.12 ± 0.88) × 10 [2]. This value is somewhat larger than the previous Belle result of (2.01±0.15±0.20± 0.52) × 10 from 152 × 10 Υ(4S) → BB decays [8]. Both papers see clear signals forB → Σc(2455)p̄ in the Dalitz plot, but a small or no signal forB → Σc(2520)p̄. Both papers also observed a Λ+c p̄ threshold enhancement, discussed later. In addition, BABAR noted a broad, statistically significant (5.8σ) peak in Λ+c π − which is welldescribed by a relativistic D-wave Breit-Wigner with mass 2846 ± 8 MeV/c and width 86 −22 MeV, as illustrated in Fig. 1. This region of the Dalitz plot is populated in the Belle data, but it is not clear whether a significant structure with the same parameters is present. The closest known resonance is the Σc(2800) [9]: the widths are consistent but the mass obtained by BABAR differs from the nominal value, 2802± 4± 7 MeV/c, by around three standard deviations. This difference is intriguing but not conclusive. An updated study by Belle with their large Υ(4S) dataset could settle this question and establish whether BABAR saw the Σc(2800) with a downward fluctuation in mass or an entirely new state. BABAR also used the largeB → Σc(2455)p̄ signal to determine the spin of the Σc(2455); the state is predicted to have J = 1/2 in the quark model but neither quantum number has been measured. BABAR performed an angular analysis of the decay under the assumption that J(Λ+c ) =