Is the resonance D(2637) really a radial excitation?

Abstract

We consider various possible identifications of the quantum numbers of the resonance D(2637) recently observed by DELPHI in the $D^*\pi\pi$ channel. We argue that in spite of a good agreement of the measured mass with the quark-model prediction for the radial excitation, a total width as small as $\le 15$ MeV is hardly compatible with its identification as a radial charm excitation. The $J^{P}=2^{-}, 3^{-}$ orbitally excited mesons with such a mass could have widths of the observed order of magnitude. However in this case one would expect two neighbouring states with the mass difference of about 30-50 MeV corresponding to the nearly degenerate components of the heavy- meson multiplet with light-quanta angular momentum j=5/2, and moreover, according to the quark-model predictions the mass of the orbital excitation should be more than 50 MeV larger than 2637 MeV. Thus we conclude that, at present, we find no fully convincing understanding of the quantum numbers of the observed resonance.