Nucleon–antinucleon bound states suggested

Does positronium have an analogy in the nucleon–antinucleon system? The existence of such narrow bound states is a possible explanation for results of a recent experiment that seem to contradict predictions of charge independence. Specifically, a team from Syracuse University, New York and from the Nuclear Research Center Demokritos in Athens, Greece found that in pionic annihilations at rest of antiprotons on deuterium, the resulting charged pions carried away less energy than is expected if the strong interaction forces are independent of charge. The Syracuse–Athens team then gathered evidence that the “missing” energy is taken away by an excess number of gamma rays; that is, more gamma rays than should be produced by decay of the neutral pions into two gammas. The experimenters feel that these extra gammas represent electromagnetic transitions between narrow nucleon–antinucleon resonances or bound states, which they have named “cosmion.” If their interpretation is correct then perhaps such narrow nucleon–antinucleon resonances or bound states are connected to the newly discovered J or ψ particles at 3.1 and 3.7 GeV; such is the suggestion of Alfred Goldhaber and Maurice Goldhaber. Another interesting feature of such possible states is that their characteristic gamma rays could identify regions of the universe where antimatter (if it exists) meets matter.

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