Results of a search for the hc(P11) state of charmonium in the ηcγ and J/ψπ0 decay modes

We report evidence for the hc state of charmonium in its ηcγ decay mode and lack of evidence in the J/ψπ0 mode. We studied these channels in p̄p annihilations near the center of gravity of the PJ3 states, where the hc was reported in the J/ψπ0 mode by E760, our previous experiment, at 3526.2±0.15±0.2MeV, with ΓR≤1MeV. We observe an event excess in the ηcγ mode near 3526 MeV. Testing the null hypothesis of a linearly varying background cross section against the alternate hypothesis that includes a resonance near 3526 MeV, we reject the null hypothesis with P∼0.001. The resonance mass is 3525.8±0.2±0. 2MeV and the resonance width ≤1MeV. We estimate 10.0±3. 5<Γp̄pBηcγ<12.0±4.5eV, corresponding to fixed values 0.5<ΓR<1.0MeV. We find no event excess within the search region in the J/ψπ0 mode.