Results of a search for the h c ( 1 P 1 ) state of charmonium in the η c γ and J/ψπ 0 decay modes

We report evidence for the h{sub c} state of charmonium in its {eta}{sub c}{gamma} decay mode and lack of evidence in the J/{psi}{pi}{sup 0} mode. We studied these channels in pp annihilations near the center of gravity of the {sup 3}P{sub J} states, where the h{sub c} was reported in the J/{psi}{pi}{sup 0} mode by E760, our previous experiment, at 3526.2{+-}0.15{+-}0.2 MeV, with {gamma}{sub R}{<=}1 MeV. We observe an event excess in the {eta}{sub c}{gamma} 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{approx}0.001. The resonance mass is 3525.8{+-}0.2{+-}0.2 MeV and the resonance width {<=}1 MeV. We estimate 10.0{+-}3.5<{gamma}{sub pp}B{sub {eta}{sub c}}{sub {gamma}}<12.0{+-}4.5 eV, corresponding to fixed values 0.5<{gamma}{sub R}<1.0 MeV. We find no event excess within the search region in the J/{psi}{pi}{sup 0} mode.