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

Jiunn-Wei Chen·Xiangdong Ji
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Abstract

We show that polarized gamma p -> π^+ n in the threshold region is an excellent candidate for measuring the leading parity-violating pion-nucleon coupling h_{πNN}^{(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_γ|_{th} = \sqrt{2} f_π(μ_p-μ_n) h_{πNN}^{(1)}/g_A m_N \sim h_{πNN}^{(1)}/2, and its strong dominance at forward and backward angles in the threshold region.

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Jiunn-Wei Chen, Xiangdong Ji. 2001-02-13. Measuring the P-odd Pion-Nucleon Coupling h_{πNN}^{(1)} in π^+ Photoproton Production Near the Threshold. https://doi.org/10.1103/physrevlett.86.4239

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