Observation of an excited state of a pion: a new pseudoscalar meson
Bellini G., Vasilevskii I. M., Vegni G., Vishnyakov V. V., Di Corato M., Zaimidoroga O. A., Ivan'shchin Yu. I., Lytkin L. K., Palombo F., Pernegr J., Sala A., Sala S., Sychkov S. Ya., Tyapkin A. A., Frabetti P.-L.
A new pseudoscalar meson has been discovered by a partial-wave analysis of a π+π~π~ system produced during the diffractive dissociation of тг mesons with a momentum of 40 GeV/c by nuclei. This new pseudoscalar meson has a mass of 1.205±0.007 GeV/c2, a width of 0.320±0.035 GeV/c2, and quantum numbers IGJP = 1~0~. In a quark-structure interpretation, this new particle is a radial excitation of a pion.