Measurements of the Mass, total Width and Two-Photon Partila Width of the ${\eta }_c$ Meson

Abstract

Using 13.4 $f{b}^{-1}$ of data collected with the CLEO detector at the Cornell Electron Storage Ring, we have observed 300 events for the two-photon production of ground-state pseudo-scalar charmonium in the decay ${\eta }_c$ -> $K_S{K}^{\mp }{\pi }^{\pm }$. We have measured the ${\eta }_c$ mass to be (2980.4 +- 2.3 (stat) +- 0.6 (sys)) MeV and its full width as (27.0 +- 5.8 (stat) +- 1.4 (sys)) MeV. We have determined the two-photon partial width of the ${\eta }_c$ meson to be (7.6 +- 0.8 (stat) +- 0.4 (sys) +- 2.3 (br)) keV, with the last uncertainty associated with the decay branching fraction.

9 pages postscript, also available through http://w4.lns.cornell.edu/public/CLNS