Observation of the hc 1 P 1 State of Charmonium

We have performed a search for the $^{1}$${\mathit{P}}_{1}$ state of charmonium resonantly formed in p\ifmmode\bar\else\textasciimacron\fi{}p annihilations, close to the center of gravity of the $^{3}$${\mathit{P}}_{\mathit{J}}$ states. We report results from the study of the J/\ensuremath{\psi}+${\mathrm{\ensuremath{\pi}}}^{0}$ and J/\ensuremath{\psi}+2\ensuremath{\pi} final states. We have observed a statistically significant enhancement in the p\ifmmode\bar\else\textasciimacron\fi{}+p\ensuremath{\rightarrow}J/\ensuremath{\psi}+${\mathrm{\ensuremath{\pi}}}^{0}$ cross section at \ensuremath{\surd}s \ensuremath{\simeq}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}$${\mathit{P}}_{1}$ state. In our search we have found no candidates for the reactions p\ifmmode\bar\else\textasciimacron\fi{}+p\ensuremath{\rightarrow}J/\ensuremath{\psi}+${\mathrm{\ensuremath{\pi}}}^{0}$+${\mathrm{\ensuremath{\pi}}}^{0}$ and p\ifmmode\bar\else\textasciimacron\fi{}+p\ensuremath{\rightarrow}J/\ensuremath{\psi}+${\mathrm{\ensuremath{\pi}}}^{+}$+${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$.