Measurement of the gamma gamma* --> eta_c transition form factor

TL;DR

This paper measures the eta_c meson's properties, including its mass, width, and transition form factor, using a large dataset from e+e- collisions to improve understanding of its electromagnetic structure.

Contribution

It provides new measurements of the eta_c transition form factor over a wide momentum transfer range, based on extensive data collected with the BABAR detector.

Findings

Eta_c mass measured at 2982.2 MeV/c^2

Eta_c width measured at 31.7 MeV

Transition form factor characterized from 2 to 50 GeV^2

Abstract

We study the reaction e+e- --> e+e- eta_c, eta_c --> K_S K+- pi-+ and obtain eta_c mass and width values 2982.2+-0.4+-1.6 MeV/c^2 and 31.7+-1.2+-0.8 MeV, respectively. We find Gamma(eta_c --> gamma gamma)B(eta_c --> K anti-K pi)=0.374+-0.009+-0.031 keV, and measure the gamma gamma* --> eta_c transition form factor in the momentum transfer range from 2 to 50 GeV^2. 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.