Professor Joseph M. Izen

Department of Physics, University of Texas at Dallas





A Charmonium meson is a particle made of a charm quark and an anti-charm quark. It is the hydrogen atom, or more correctly the positronium atom of meson spectroscopy.  Historically, the observation of two charmonia, the J/psi(1S)  and the psi(2S), was a crucial piece of evidence that confirmed the existence of quarks. Many charmonium excitations have since been identified by annihilating electrons and positrons or protons and antiprotons with just enough energy to produce a charm-anticharm system, and charmonium spectroscopy has been the primary yardstick for measuring the radial dependence of the strong force. After nearly three decades of routine charmonium spectroscopy, a fly has lodged itself in the ointment. The B-factories which annihilate beams electrons and positrons at over three times the energy for threshold charmonium production have developed novel techniques to observe charmonia. These experiments are finding states with masses where charmonia were not expected, culminating this past summer in the discovery of the Y(4260) which may be the most exotic of all the new states. The evidence for the Y(4260), and theoretical speculation regarding its nature will be presented.