¢-Particles and Quartet Model

The possibility that ¢-particles are vector-mesons composed of a charmed quark and an anti-charmed quark is discussed. Suggested by the hadron-lepton symmetry, quartet models of hadrons have been proposed.n.z> In these models there is a fourth quantum number (the charm quantum number) which is conserved by the strong interaction. Here, we assume a fractional charged version of the quartet model;2 ' i. e., we add a charmed quark c with quantum numbers B=1/3, Q=2/3, Y =-2/3 and C=;=1 (Q=l3 + Y/2+C) to the conventional quark model with p, n and A. quarks. The success of the SU(6) symmetric quark model suggests the SU(8) sym-metry of hadron dynamics. Then, the mesons with lightest masses are an SU(8) singlet, which is an SU(4) singlet pseudoscalar-meson r; ' with mass m., and an SU(8) 63-plet with mass m 0, which consists of SU ( 4) 15-plet pseudoscalar-mesons and SU ( 4) 16-plet vector-mesons. The degeneracy of these mesons is broken by introducing the following SU(8) symmetry-breaking interaction: (1) to the effective Lagrangian, where S is the total intrinsic spin of the quark and anti-quark, M is the 4 X 4 matrix of the field operators of the sixteen vector-mesons and fifteen pseudoscalar-mesons, and T 8 (T15) is a diagonal 4 X 4 matrix with diagonal elements 1, 1,-2 and 0 (1, 1, 1 and- 3). By.diagonalizing (1), we obtain the following results for the masses m and quark-contents of the mesons tabulated in Table I. Now we hav ~ an I = Y = C = 0 vector-meson with the quark-content cc. We identify it with a new meson3 ' </J (3105). From the masses of the observed vector-mesons we find a=0.07(GeVY and b=1.1(GeVY. (2) The masses of not-yet-discovered mesons given in Table I have been calculated by making use of (2). In order to improve the fit between the theoretical and experimental masses of the vector-mesons, we introduce additional term