Observation of eta_c^{prime} Production in gamma gamma Fusion at CLEO

TL;DR

This paper reports the first observation of the eta_c' (2S) charmonium state produced via two-photon fusion at CLEO, measuring its mass, hyperfine splitting, and two-photon decay width.

Contribution

It provides the first experimental measurement of the eta_c' (2S) mass, hyperfine splitting, and two-photon decay width in two-photon fusion at CLEO.

Findings

Mass of eta_c' measured at 3642.9 MeV

Hyperfine splitting for 2S state is 43.1 MeV

Two-photon decay width of eta_c' is 1.3 keV

Abstract

We report on the observation of the eta_{c}^{prime}(2^{1}S_{0}), the radial excitation of eta_{c}(1^{1}S_{0}) ground state of charmonium, in the two-photon fusion reaction gamma gamma rightarrow eta_{c}^{prime} rightarrow K_{S}^{0}K^{pm}pi^{mp} in 13.6 fb^{-1} of CLEO II/II.V data and 13.1 fb^{-1} of CLEO III data. We obtain M(eta_{c}^{prime})=3642.9 pm 3.1(stat) pm1.5(syst) MeV, and M(eta_{c})=2981.8 pm1.3(stat) pm 1.5(syst) MeV. The corresponding values of hyperfine splittings between ^{1}S_{0} and ^{3}S_{1} states are \Delta M_{hf}(1S)=115.1 pm 2.0 MeV, Delta M_{hf}(2S)=43.1 pm3.4 MeV. Assuming that the eta_{c} and eta_{c}^{prime} have equal branching fractions to K_{S}K pi, we obtain Gamma_{gamma gamma}(eta_{c}^{prime})=1.3 pm 0.6 keV.