Parity-violating pion–nucleon coupling hπNN(1) from π+-electroproton production near the threshold

We study the possibility of measuring parity-violating pion–nucleon coupling hπNN(1) from π+-electroproton production in the threshold region. We calculate the electron-helicity asymmetry in terms of hπNN(1) and the Z-boson exchange between the electron and proton in leading-order heavy-baryon chiral perturbation theory. From the result, we demonstrate that the coupling can be determined to an accuracy of ∼2×10−7 in an experiment with incident electron energy 250 MeV, luminosity 1038 s−1 cm−2, and a running time of 107 s.