A Search for the Singlet-P State hc(1 1P1) of Charmonium in   Proton-Antiproton Annihilations at Fermilab Experiment E835p
  We present the results of a search for the spin-singlet P-wave state hc(1 1P1) of charmonium formed through proton-antiproton annihilation at Fermilab experiment E835. The decay channels whjich were studied were ppbar -> J/psi + X -> e^+e^- + X, ppbar -> J/psi + pi0 -> e^+e^- + 2gamma, ppbar -> J/psi + pi0pi0 -> e^+e^- + 4gamma, and the neutral channel ppbar -> eta_c gamma -> (2gamma) gamma. The decay ppbar -> J/psi gamma -> e^+e^- gamma, into which 1P1 decay is forbidden by C-parity conservation, was also examined for comparison   The 90% confidence upper limits for the decay channels studied in the mass range 3525.1-3527.3 MeV for a 1P1 resonance with a presumed width of 1.0 MeV were determined to be B(ppbar->1P1)xB(1P1->J/psi+X) <= 1.8x10^-7, B(ppbar->1P1)xB(1P1->J/psi+pi0) <= 1.2x10^-7, and B(ppbar->1P1)xB(1P1->J/psi+gamma) <= 1.0x10^-7. No evidence for a 1P1 enhancement was observed in either of the two additional reactions studied. 
David N. Joffe