Measuring the P-Odd Pion-Nucleon Coupling h\(1\)πNN in π+-Photoproton Production near Threshold

We show that γ-->p-->π⁺n in the threshold region is an excellent candidate for measuring the leading parity-violating pion-nucleon coupling h^\(1\)_πNN 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 = 2 f_π\(μ_p- μ_n\)h^\(1\)_πNN/g_Am_N~h^\(1\)_πNN/2, and its strong dominance at forward and backward angles in the threshold region.