Charmonium Spectroscopy from Radiative Decays of the J/ψ and ψ'

Data were collected at the Stanford Linear Accelerator Center's electron-positron colliding beam machine, SPEAR, intermittently over a two and half year period, beginning at the end of 1978. The Crystal Ball detector consists of a highly segmented array of 732 NaI(Tl) crystals (16 radiation lengths) covering ≅ 98% of 4π steradians, and is used to measure the photon energies, directions, and lateral shower distributions. Centrally located spark and proportional chambers are used for charged particle recognition. as a result, this detector is excellently suited for studying the radiative transitions among the charmonium family of states: i) from ψ' to the triplet P states, x(3415), x(3510), and x(3550); ii) from ψ' and J/ψ to the singlet S state n_c(2984); and iii) from ψ' to the radially excited singlet S state n_c'(3592). The analysis of 1.8 ∙ 10⁶ ψ' and 2.2 ∙ 10⁶ J/ψ decays yields the following spectrum of states: x₀(3418), x₁(3512), x₂3558), n_c(2984), and n_c'(3592), each with a ± 4 MeV error on its mass. The branching ratios are measured to be: B(ψ'→yx_0,1,2) = (9.9 ± 0.5 ± 0.8)%, (9.0 ± 0.5 ± 0.7)%, and (8.0 ± 0.5 ± 0.7)%, respectively; B(ψ'→yn_c) = (0.28 ± 0.06)% and B(J/ψ→yn_c) = (1.27 ± 0.36)%; and B(ψ'→yn_c) = (0.5 - 1.2)% at the 90% confidence level. Values for the natural line widths are obtained: Γ(x_0,1,2) = (13.5 - 20.4) MeV, < 3.8 MeV, (0.85 - 4.9) MeV, respectively (90% C.L.); Γ(n_c) = (11.5 + 4.5/ - 4.0) MeV; and Γ(n_c') < 7 MeV (90% C.L.). The cascade product branching ratios B(ψ'→yx_J) ∙ B(x_J → yJ/ψ) were measured for J = 1 and 2 to be: (2.56 ± 0.12 ± 0.20)% and (0.99 ± 0.10 ± 0.08)% respectively. No signal was seen for the J= 0 transition, with an upper limit above its previously measured product branching ratio. The results of this analysis are compared with the predictions of the charmonium models.

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