Observation of ?c+?np+? and search for ?c+?na0980+

By analysing 6.1 fb^-1 of data collected at centre-of-mass energies between s=4.600 and 4.843 GeV with the BESIII detector at the BEPCII collider, we observe the decay ?c+?np+? for the first time with a statistical significance of 9.5s. The ratio of branching fractions B?c+?np+?/B?c+??p+? is measured to be 0.155 ± 0.031_stat. ± 0.012_syst. Taking the world average of B?c+??p+? as reference, the absolute branching fraction is calculated to be B?c+?np+?=2.94±0.59stat.±0.23syst.±0.13ref.×10-3. The intermediate process ?c+?na0980+ is also searched for in the p⁺? invariant mass spectrum. Since no significant signal is found, the upper limit on B?c+?na0980+×Ba0980+?p+? is set to 8.4 × 10^-4 at 90% confidence level. A sophisticated deep learning approach using a Transformer-based architecture is employed to distinguish signals from prevalent hadronic backgrounds, complemented by thorough validation and systematic uncertainty quantification.