Observation of inverse electroproduction of pions on 12C nucleus at 164 MeV pion energy and determination of F1v nucleon form factor

An experiment on detection of inverse electroproduction of pions (IEP) on carbon nuclei (π-12C → e+e-X) has been carried out, the kinetic energy of pions being 164 MeV. Electrons and positrons were detected. The product of solid angles of the set-up is 1.48 sr2. Processing yielded ∼160 events of the IEP reaction. The experimental value of the cross section for the IEP reaction on the carbon nucleus was Δσ(12C)=(27.6±4.7)x10-33 cm 2 if the electron and positron energies exceed 60 MeV, and their emission angles are Θ ∼ 90 deg in the lab system. Hence the following value is obtained for the differential cross section of the IEP process on a proton (π-p → e+e-n) under the same conditions: d2δ/dΩ2(p)=(5.3±1.1)x10-33 cm2/sr2, taking into account screening of protons. The Dirac isovector form factor on the nucleon is found to be F1V=1.15±0.09 for the squared four-momentum of the photon K2=0.055 (GeV/c)2