Measurements of the mass and width of the eta_c meson and of an eta_c(2S) candidate

TL;DR

This paper reports precise measurements of the eta_c meson’s mass and width, and provides evidence for the eta_c(2S) state using two-photon interactions at the SLAC B-Factory with the BABAR detector.

Contribution

The study presents the first detailed measurements of eta_c(2S) candidate properties in two-photon interactions, improving understanding of charmonium states.

Findings

eta_c mass: 2982.5 MeV/c2

eta_c width: 34.3 MeV/c2

eta_c(2S) candidate observed with mass 3630.8 MeV/c2

Abstract

The mass and total width of the eta_c meson have been measured in two-photon interactions at the SLAC asymmetric B-Factory with the BABAR detector. With a sample of approximately 2500 reconstructed eta_c -> Ks K pi decays in 88 fb-1 of data, the measured eta_c mass and width are respectively 2982.5 +- 1.1 (stat) +- 0.9 (syst) MeV/c2 and 34.3 +- 2.3 (stat) +- 0.9 (syst) MeV/c2. Using the same decay mode, a second resonance with 112 +- 24 events is observed with a mass of 3630.8 +- 3.4 (stat) +- 1.0 (syst) MeV/c2 and width of 17.0 +- 8.3 (stat) +- 2.5 (syst) MeV/c2. This observation is consistent with expectations for the eta_c(2S) state.