Measurement of the resonance parameters of the charmonium ground state, eta(c)(1(1)S(0))

The resonance parameters of the charmonium ground state, eta(c)(1(l)S(0)), have been measured by means of the reaction (p) over barp --> eta(c) --> gammagamma. The mass and total width are determined to be 2984.1 +/- 2.1 +/- 1.0 MeV/c(2) and 20.4(-6.7)(+7.7) +/- 2.0 Mev, respectively. The product of branching ratios B((p) over barp --> eta(c))B(eta(c) --> gammagamma) is determined to be (22.4(-3.7)(+3.8) +/- 2.0) x 10(-8), from which B(eta(c) --> gammagamma) = (1.87(-0.31-0.50)(+0.32+0.95)) x 10(-4), and Gamma(eta(c) --> gammagamma) = 3.8(-1.0-1.0)(+1.1+1-9) keV are derived using B(eta(c) --> (p) over barp) (12 +/- 4) x 10(-4) from the literature. (C) 2003 Published by Elsevier B.V.