CLAS12 - The Hall B 12GeV Upgrade
CLAS12 detector has evolved from CLAS to meet the basic requirements for the study of the structure of nucleons and nuclei after the CEBAF energy upgrade to 12 GeV. A major focus of CLAS12 will be the access to the generalized parton distributions (GPDs) in exclusive reactions such as deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP). The cross sections are small and high luminosity combined with large solid angle coverage is needed for an efficient GPD program. Studies of the nucleon spin structure and the transverse momentum dependent parton distributions (TMDs) require large acceptance and the use of polarized targets that can only be operated at limited luminosity. At the higher energies, new requirements on particle identification make improvements in electron/pion separation, particle timing, and calorimeter granularity necessary. The increase in operating luminosity of more than an order of magnitude requires better magnetic shielding of Moller electrons which is achieved by a solenoid magnet and smaller drift cells. The forward part of CLAS12 retains the six sector symmetry of CLAS to make use of existing detectors, while the central part is based on a small solenoid magnet with full cylindrical symmetry.