The CLAS12 Spectrometer at Jefferson Laboratory

Abstract

The CEBAF Large Acceptance Spectrometer for operation at 12 GeV beam energy (CLAS12) in Hall B at Jefferson Laboratory is used to study electro-induced nuclear and hadronic reactions. This spectrometer provides efficient detection of charged and neutral particles over a large fraction of the full solid angle. CLAS12 has been part of the energy-doubling project of Jefferson Lab's Continuous Electron Beam Accelerator Facility, funded by the United States Department of Energy. An international collaboration of over 40 institutions contributed to the design and construction of detector hardware, developed the software packages for the simulation of complex event patterns, and commissioned the detector systems. CLAS12 is based on a dual-magnet system with a superconducting torus magnet that provides a largely azimuthal field distribution that covers the forward polar angle range up to 35 • , and a solenoid magnet and detector covering the polar angles from 35 • to 125 • with full azimuthal coverage. Trajectory reconstruction in the forward direction using drift chambers and in the central direction using a vertex tracker results in momentum resolutions of <1% and <3%, respectively. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 10 35 cm −2 s −1 . These capabilities are being used in a broad program to study the structure and interactions of nucleons, nuclei, and mesons, using polarized and unpolarized electron beams and targets for beam energies up to 11 GeV. This paper gives a general description of the design, construction, and performance of CLAS12.

The CLAS12 high threshold Cherenkov counter

“…The CLAS12 spectrometer in Hall B at Jefferson Laboratory (JLab) has been designed and built for comprehensive experimental studies of matter, using primarily a high-energy electron beam [1]. For these experiments this spectrometer must be capable of detecting scattered electrons within the entirety of its forward acceptance range and at the highest possible efficiency with low background.…”

The CLAS12 superconducting magnets

“…A general overview of the physics requirements and experiment design in provided in Ref. [1]. Tables I and II summarize the physics requirements for the torus and solenoid superconducting magnets, respectively, while Table III provides a summary of the key design parameters for the two magnets.…”

“…1 Use safety factor of 5 where Kapton is used and 10 if no Kapton is used [9]. * Rare hardware fault case resulting in approximately 500 V across the dump resistor…”

The CLAS12 Micromegas Vertex Tracker

“…The baseline design of the Hall B CEBAF Large Acceptance Spectrometer for use at the 12 GeV Jefferson Laboratory (JLab) facility (CLAS12) [1] includes two tracking detector systems. A Silicon Vertex Tracker (SVT) [2] consists of a polyhedral arrangement around the target and resides in a 5 T solenoid magnetic field to detect particles emitted between 35 • and 125 • with respect to the beam direction.…”