Measurement of eta eta production in two-photon collisions

TL;DR

This paper presents the first measurement of the differential cross section for eta eta production in two-photon collisions over a broad energy and angular range, analyzing resonance contributions and comparing results with theoretical models.

Contribution

It provides the first experimental data on gamma gamma --> eta eta differential cross sections and resonance analysis in this energy range, including chi_{cJ} contributions.

Findings

First measurement of eta eta production cross section in gamma gamma collisions.

Analysis of resonance amplitudes for various partial waves.

Comparison of high-energy data with theoretical models.

Abstract

We report the first measurement of the differential cross section for the process gamma gamma --> eta eta in the kinematic range above the eta eta threshold, 1.096 GeV < W < 3.8 GeV over nearly the entire solid angle range, |cos theta*| <= 0.9 or <= 1.0 depending on W, where W and theta* are the energy and eta scattering angle, respectively, in the gamma gamma center-of-mass system. The results are based on a 393 fb^{-1} data sample collected with the Belle detector at the KEKB e^+ e^- collider. In the W range 1.1-2.0 GeV/c^2 we perform an analysis of resonance amplitudes for various partial waves, and at higher energy we compare the energy and the angular dependences of the cross section with predictions of theoretical models and extract contributions of the chi_{cJ} charmonia.