Lingyun Dai

JLab, Newport News, VA

A Comprehensive Amplitude analysis of two photon processes


Two photon processes attracted long interest as it is one of the cleanest ways of probing hadron structure. Especially the two photon coupling is a key guide to the composition of states appear in two photon processes. In this presentation we will perform an amplitude analysis on photon-photon scattering into pion and kaon pairs below 1.5 GeV. To get a model independent amplitude, we impose the basic constraints required by analyticity, unitarity, and crossing-symmetry. One constraint is from Final State Interaction Theorem (unitarity). To fix the hadronic amplitudes, we include the latest hadronic ππ, KK scattering amplitudes given by dispersive analysis, supplemented by the recent Dalitz plot analysis near the KK threshold region from BaBar. With these hadronic amplitudes and applying Final State Interaction Theorem, we give an overall fit of γ γ-->π π datasets, including the high statistics neutral pion data of Belle. A region of solutions are found and what should be emphasized is, the relatively poor integrated cross-section data on γ γ -->K K narrows the patch of solutions to essentially a single form. Finally we present the two photon couplings of scalars and tensors.


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