Recent BABAR Results on Two-photon Physics

TL;DR

The BABAR experiment studied two-photon processes, measuring properties of charmonium states and transition form factors, revealing significant differences in meson distribution amplitudes.

Contribution

This work provides new high-statistics measurements of eta_c and eta_c(2S) properties and first-time analysis of certain decay modes, advancing understanding of meson structure.

Findings

Measured eta_c and eta_c(2S) masses and widths.

Determined decay probability ratios for specific meson modes.

Extracted photon-meson transition form factors and identified differences in meson distribution amplitudes.

Abstract

Recent BABAR results on two-photon processes are presented. A high statistics study of the two-photon production of the charmonium states eta_c and eta_c(2S) is performed. The mass and width of eta_c and eta_c(2S) are measured; the ratio of the decay probabilities to KS K+pi- and K+K-pi+pi-pi0 are determined. The latter mode is studied for the first time. The reactions e+e- --> e+e- gamma* gamma* --> e+e- + pseudoscalar meson are studied in the single-tag mode for pi0, eta, eta', and eta_c. From the measured differential cross sections the Q^2 dependencies of the photon-meson transition form factors are extracted. From these measurements we conclude that the pion distribution amplitude strongly differs from the distribution amplitudes of eta and eta' mesons.