The BONuS12 Experiment Measuring the Neutron Structure Function at large Bjorken-x

The BONuS experiment using Jefferson Lab’s CLAS detector studied the nearly free neutron structure by using the spectator tagging technique. The backscattered spectator protons in d(e, e′p)X deep-inelastic scattering with momenta <100 MeV/c are detected by a Radial Time Projection Chamber (RTPC), thereby selecting electron-scattering events off nearly free neutrons. The recent upgrade of Jefferson Lab to 11 GeV electron beam energy will extend the kinematic range to a higher Bjorken x of ∼ 0.85. The collaboration is presently preparing the BONuS12 experiment, which is expected to take data in early 2020 using the upgraded CLAS12 detector. A new and enlarged RTPC is being built which utilizes a new drift gas and a new data acquisition system, and new simulation and particle tracking software is being developed. This presentation includes a status update of the BONuS12 experiment with an overview of the spectator tagging technique to study the free neutron structure function.