Measurement of the p(e,e′π+)n reaction close to threshold and at low Q2

The cross section of the p(e,e′π+)n reaction has been measured for five kinematic settings at an invariant mass of W=1094MeV and for a four-momentum transfer of Q2=0.078(GeV/c)2. The measurement has been performed at MAMI using a new short-orbit spectrometer (SOS) of the A1 collaboration, intended for detection of low-energy pions. The transverse and longitudinal cross section terms were separated using the Rosenbluth method and the transverse-longitudinal interference term has been determined from the left-right asymmetry. The experimental cross section terms are compared with the calculations of three models: DMT2001, MAID2007 and χMAID. The results show that we do not yet understand the dynamics of the fundamental pion.