A radial time projection chamber for α detection in CLAS at JLab

A new Radial Time Projection Chamber (RTPC) was developed at the Jefferson Laboratory to track low-energy nuclear recoils to measure exclusive nuclear reactions, such as coherent deeply virtual Compton scattering and coherent meson production off ${}^4$He. In 2009, we carried out these measurements using the CEBAF Large Acceptance Spectrometer (CLAS) supplemented by the RTPC positioned directly around a gaseous ${}^4$He target, allowing a detection threshold as low as 12 MeV for ${}^4$He. This article discusses the design, principle of operation, calibration methods and performances of this RTPC.