Double-pion electroproduction off protons in deuterium: quasi-free cross sections and final state interactions*

The talk will present new information on the fully integrated and single-differential cross sections of charged double-pion electroproduction off protons bound in a deuteron. The study became possible owing to the experiment of electron scattering off a deuterium target conducted in Hall B at JLab with the CLAS detector. The measurements were performed in the kinematic region of the invariant mass $W$ from 1.3~GeV to 1.825~GeV and photon virtuality $Q^{2}$ from 0.4~GeV$^2$ to 1.0~GeV$^2$. Sufficient experimental statistics allowed for narrow binning, while maintaining adequate statistical uncertainties. The obtained cross sections are quasi-free, meaning that the admixture of events, in which the final hadrons interacted with the spectator neutron, was kinematically reduced to the achievable minimum. The extracted quasi-free cross sections were compared with the corresponding cross sections off free protons, which allowed us to obtain an estimate of the contribution from events in which interactions between the final-state hadrons and the spectator neutron took place.