Opportunities for studying C+ resonances at 3--12 GeV photon collider

Abstract

Recently, a γγ collider based on existing 17.5 GeV linac of the European XFEL has been proposed. High energy photons will be generated by Compton scattering of laser photons with a wavelength of 0.5-1 µm on electrons. Such photon collider covers the range of invariant masses W γγ < 12 GeV. The physics program includes spectroscopy of C+ resonances (c-, b-quarkonia, 4-quark states, glueballs) in various J P states. Variable circular and linear polarizations will help in determining the quantum numbers. In this paper, we present a summary of measured and predicted two-photon widths of various resonances in the mass region 3-12 GeV and investigate the experimental possibility of observing these heavy two-photon resonances under conditions of a large multi-hadron background. Registration of all final particles is assumed. The minimum values of Γ γγ for detecting resonances at the 5 sigma level are obtained.

χc2 tensor meson transition form factors in the light front approach

“…The production of C-even quarkonia in γ * γ fusion processes keeps providing us with important information on their structure [1][2][3][4][5][6][7][8]. While untagged e + e − cross sections give access to the decay width of quarkonia into γγ pair, in single tagged collisions, transition form factors involving one virtual and one real photon can be measured.…”