Measuring the P-odd Pion-Nucleon Coupling h_{πNN}^{(1)} in π^+ Photoproton Production Near the Threshold

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Abstract
We show that polarized gamma p -> \pi^+ n in the threshold region is an excellent candidate for measuring the leading parity-violating pion-nucleon coupling h_{\pi NN}^{(1)} to an uncertainty of 20% if it has a natural size from dimensional analysis. The conclusion is based on a large unpolarized cross section, a new low-energy theorem for the photon polarization asymmetry at the threshold A_\gamma|_{th} = \sqrt{2} f_\pi (\mu_p-\mu_n) h_{\pi NN}^{(1)}/g_A m_N \sim h_{\pi NN}^{(1)}/2, and its strong dominance at forward and backward angles in the threshold region.

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