1306.5991 (Krzysztof M. Graczyk)

Comparison of Neural Network and Hadronic Model Predictions of TPE
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Krzysztof M. Graczyk

Predictions for the two-photon exchange (TPE) correction to unpolarized $ep$ elastic cross section, obtained within two different approaches, are confronted and discussed in detail. In the first one the TPE correction is extracted from the experimental data by applying the Bayesian neural network (BNN) statistical framework. In the other the TPE is given by box diagrams, with the nucleon and $P_{33}$ resonance as the hadronic intermediate states. Two different form factor parametrizations for both the proton and the $P_{33}$ resonance are taken into consideration. Proton form factors are obtained from the global fit of the full model (with the TPE correction) to the unpolarized cross section data. Predictions of the two methods agree well in the intermediate $Q^2$ range, namely $(1,3)$ GeV$^2$. Above $Q^2=3$ GeV$^2$ the agreement is on $2\sigma$ level. Below $Q^2=1$ GeV$^2$ consistency between both approaches is broken. The values of the proton radius extracted within both models are given and their relevance is discussed. In both cases the predictions for VEPP-3 experiment have been obtained and confronted with preliminary experimental results.

View original: http://arxiv.org/abs/1306.5991