Charmonium resonances in the 3.9 GeV/c2 energy region and the X(3915)/X(3930) puzzle

Abstract

An interesting controversy has emerged challenging the widely accepted nature of the X(3915) and the X(3930) resonances, which had initially been assigned to the χc0(2P) and χc2(2P)cc¯ states, respectively. To unveil their inner structure, the properties of the JPC=0++ and JPC=2++ charmonium states in the energy region of these resonances are analyzed in the framework of a constituent quark model. Together with the bare qq¯ states, threshold effects due to the opening of nearby meson–meson channels are included in a coupled-channels scheme calculation. We find that the structure of both states is dominantly molecular with a probability of bare qq¯ states lower than 45%. Our results favor the hypothesis that X(3915) and X(3930) resonances arise as different decay mechanisms of the same JPC=2++ state. Moreover we find an explanation for the recently discovered M=3860MeV/c2 as a JPC=0++ 2P state and rediscover the lost Y(3940) as an additional state in the JPC=0++ family.