Measurement of the gamma gamma* --> etac transition form factor
Abstract
We study the reaction e+e- --> e+e- etac, etac --> KS K+- pi-+ and obtain etac mass and width values 2982.2+-0.4+-1.6 MeV/c2 and 31.7+-1.2+-0.8 MeV, respectively. We find Gamma(etac --> gamma gamma)B(etac --> K anti-K pi)=0.374+-0.009+-0.031 keV, and measure the gamma gamma* --> etac transition form factor in the momentum transfer range from 2 to 50 GeV2. The analysis is based on 469 fb-1 of integrated luminosity collected at PEP-II with the BABAR detector at e+e- center-of-mass energies near 10.6 GeV.
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