Eur. Phys. J. C (2007) 52: 159-171
https://doi.org/10.1140/epjc/s10052-007-0337-0

Regular Article - Theoretical Physics

Flavour structure of low-energy hadron-pair photoproduction

¹ Institute of Physics, Academia Sinica, Nankang, Taipei, Taiwan 11529,
² Physics Division, National Center for Theoretical Sciences, Hsinchu, Taiwan 300,

^* e-mail: odagirik@phys.sinica.edu.tw

Received: 20 January 2006
Revised: 15 June 2006
Published online: 17 July 2007

Abstract

We consider the process γγ→H₁H̄₂, where H₁ and H₂ are either mesons or baryons. The experimental findings for such quantities as the pp̄ and K_SK_S differential cross sections, in the energy range currently probed, are found often to be in disparity with the scaling behaviour expected from hard constituent scattering. We discuss the long-distance pole–resonance contribution in understanding the origin of these phenomena, as well as the amplitude relations governing the short-distance contribution, which we model as a scaling contribution. When considering the latter, we argue that the difference found for the K_SK_S and the K⁺K^- integrated cross sections can be attributed to the s-channel isovector component. This corresponds to the ρω→a subprocess in VMD (vector-meson-dominance) language. The ratio of the two cross sections is enhanced by the suppression of the φ component, and it is hence constrained. We give similar constraints to a number of other hadron-pair production channels. After writing down the scaling and pole–resonance contributions respectively, the direct summation of the two contributions is found to reproduce some salient features of the pp̄ and K⁺K^- data.