Observation of the P11 state of charmonium

We have performed a search for the 1 P 1 state of charmonium resonantly formed in pp annihilations, close to the center of gravity of the 3 P J states. We report results from the study of the J/ψ+π 0 and J/ψ+2π final states. We have observed a statistically significant enhancement in the p+p→J/ψ+π 0 cross section at √s≃3526.2 MeV. This enhancement has the characteristics of a narrow resonance of mass, total width, and production cross section consistent with what is expected for the 1 P 1 state