Observation of Excited Charmed Mesons.

Using the Tagged Photon Spectrometer and a high energy photon beam, Fermi-lab experiment E691 was able to collect a large sample (>10 ^4) of fully reconstructed charmed particles. This data set is used to search for P-wave charmed mesons (called D^{**}'s). Evidence is found for a state of mass 2459 +/- 3 (stat) +/- 2 (syst) MeV/c ^2 and width 21_sp{-8 }{+12}+/- 5 MeV/c^2 which decays to D^+pi^ -. The statistical significance of the signal is measured to be greater than 5 standard deviations. Various arguments suggest that the state is the J^ P = 2^+ P-wave charmed meson but neither the spin nor parity is measured directly. The fraction of D^+ coming from D ^{**o}(2459) is.07 +/- .02 +/-.02. Also, the D ^{**o}(2420) to D^{*+}pi^- decay observed previously in e^{+}e ^- experiments is confirmed. Finally, a 4 standard deviation signal is observed in the D ^{circ}pi^{+} ^ectrum. This is interpreted as evidence for the decay of the charged counterpart of the D^ {**o}(2420) to D^{*0 }pi^+, with the neutral from the D^{*o} decay going unobserved. The mass and width of the state are 2443 +/- 7 +/- 5 MeV/c^2 and 41 +/- 19 +/- 8 MeV/c^2, respectively. The fraction of D^{*+} coming from D^{**o}(2420) and the fraction of D^{*o} coming from the charged counterpart of the D^{**o }(2420) are measured to be consistent.