CLAS12 detector

CLAS12 detector. The CLAS12 (CEBAF Large Acceptance Spectrometer for 12 GeV) is a state-of-the-art particle detector located in Experimental Hall B at the Thomas Jefferson National Accelerator Facility (Jefferson Lab). It is the central instrument for the nuclear physics research program following the CEBAF energy upgrade to 12 GeV. The detector is designed to study the internal structure of hadrons, particularly nucleons and mesons, by detecting particles produced in high-energy collisions of an electron beam with various fixed targets.

Overview

The CLAS12 detector is the successor to the original CLAS detector, which operated during the 6 GeV era of CEBAF. Its construction and commissioning were central to the scientific mission of the 12 GeV Upgrade project at Jefferson Lab. The primary goal of the CLAS Collaboration is to explore the three-dimensional structure and internal dynamics of protons and neutrons in the regime where the strong interaction is described by Quantum Chromodynamics (QCD). It achieves this by measuring exclusive reactions and semi-inclusive deep inelastic scattering with high precision over a large solid angle.

Design and Components

The CLAS12 detector is a complex, multi-component magnetic spectrometer system designed for nearly 4π coverage. Its design is optimized for the detection of charged particles, photons, and neutrons produced in electron-nucleus collisions. The central detector, situated around the target, includes a high-intensity solenoid magnet and tracking systems like the Central Vertex Tracker (CVT) and the Barrel Micromegas Tracker. The forward detector, covering polar angles from approximately 5° to 40°, utilizes a six-sector toroidal magnet and incorporates Drift chambers, Time-of-flight scintillators, Cherenkov counters, and Electromagnetic calorimeters. Key subsystems also include the Forward Tagger for detecting very forward-scattered electrons and the Neutron Detector for identifying neutral hadrons.

Physics Capabilities

CLAS12 enables a broad program in hadron physics and nuclear physics by providing detailed measurements of Generalized Parton Distributions (GPDs) and Transverse Momentum Dependent parton distribution functions (TMDs). These functions are crucial for constructing a multi-dimensional picture of nucleon structure. The detector is uniquely capable of studying hadron spectroscopy, including the search for hybrid mesons and exotic hadrons that may reveal explicit gluonic degrees of freedom. Its large acceptance is also vital for investigating short-range correlations in nuclei and performing precision tests of the Standard Model through measurements of parity-violating asymmetries.

Technical Specifications

The CLAS12 detector operates with the continuous electron beam from CEBAF, which can deliver currents up to several microamperes at energies up to 11 GeV. The central solenoid provides a magnetic field of up to 5 T, while the six-coil toroidal magnet in the forward region generates a field integral suitable for momentum analysis. Particle identification is achieved through combined measurements of momentum, velocity, and energy loss, with timing resolutions on the order of tens of picoseconds in the Time-of-flight systems. The Electromagnetic calorimeter provides photon detection with an energy resolution of approximately 5%/√E.

Operation and Experiments

Since achieving first beam in 2017, CLAS12 has been the workhorse for a significant portion of the experimental program following the 12 GeV Upgrade. It operates within the framework of the Jefferson Lab user program, hosting numerous experiments proposed by international collaborations. Major research initiatives include the Deeply Virtual Compton Scattering (DVCS) program to map GPDs, the SIDIS program to extract TMDs, and dedicated runs for nucleon resonance spectroscopy and studies of nuclear transparency. Data from CLAS12 are analyzed using the ROOT framework and the CLAS12 software suite, with results contributing to global efforts in understanding strong force phenomena.

Category:Particle detectors Category:Nuclear physics experiments Category:Thomas Jefferson National Accelerator Facility