Medium effects in pion electroproduction off 3He

The differential coincident pion electroproduction cross section in the 3He(e,e')π+)3H reaction has been measured with the high resolution three-spectrometer facility at the Mainz Microtron MAM1. Two kinds of measurements were performed: for fixed four-momentum transfers Q2 = 0.045 (0.1)(GeV/c)2 with the pions detected in parallel kinematics, the incident energy was varied between 555 and 855 MeV in order to enable a separation of the longitudinal and transverse structure functions. In the second case the pion emission angle with respect to the momentum transfer direction was varied over a large range at fixed incident energy E0 = 855 MeV and fixed four-momentum transfers Q2 = 0.045 (0.1)(GeV/c)2. From the angular distributions the LT interference term can be extracted. The experimental data are compared to model calculations assuming standard Born amplitudes, including Δ and higher resonance terms and accounting for the final state interaction of the outgoing pion. The effects of medium modifications of the Δ and of the pion are discussed