The CLAS12 high threshold Cherenkov counter

Abstract

The High Threshold Cherenkov Counter (HTCC) is one of the detector systems of the CLAS12 spectrometer, and is used to generate a fast trigger signal in electron scattering experiments in the polar angle range from 5 • to 35 • . The HTCC is installed in front of the drift chambers and introduces a minimal amount of additional material within the acceptance. The HTCC is one unit whose core component is a multifocal mirror that consists of 60 lightweight ellipsoidal mirrors. It is important that the HTCC provides efficient coverage of the CLAS12 forward acceptance with no gaps. In order to achieve this, each sector of the CLAS12 Forward Detector is covered by 2 identical half-sector mirrors that focus Cherenkov light on 8 phototubes. The HTCC has a total of 48 channels with Electron Tubes 9823QKB photomultipliers that have a 5-in quartz face plate to detect Cherenkov light. The system provides rejection of charged π-mesons with momenta below 4.8 GeV for the reliable identification of scattered electrons. In this paper the details of the design, construction, calibration, and performance results of the HTCC are presented. 10 (see Fig. 1) of CLAS12 was designed and built to fulfill the goal of detecting scattered electrons in the range of polar angles from 5 • to 35 • in conjunction with other detector systems of the CLAS12 Forward Detector and to generate a fast trigger signal 15 for event readout.The distinguishing features of the detector were influenced by its location in front of the drift chambers (DC) [2], which required that the HTCC incorporate a minimum amount of material in the 20 active area in front of the tracking detectors. Because the HTCC is a single module system, it occupies very limited space within CLAS12. Consequently, the construction requirements (including transportation to the hall and installation into the 25 nominal location of the detector) were important for its structural design.

Beam-recoil transferred polarization in K+Y electroproduction in the nucleon resonance region with CLAS12

“…The Forward Detector also consists of different types of Cherenkov detectors. Of relevance in this work is a CO 2 -filled high threshold Cherenkov detector that spans the full azimuthal range, which is used as part of the trigger selection for electrons [46]. The Central Detector consists of a multi-layer vertex tracker [47,48] surrounded by a barrel of scintillation counters for charged particle identification [49] via precision flight time measurements.…”

The CLAS12 Central Time-of-Flight system

“…Downstream of the torus each sector is nominally instrumented with a Cherenkov counter for π/K separation, a scintillation counter hodoscope for charged particle time measurements, and an electromagnetic calorimeter system for electron and neutral particle identification. Just upstream of the torus is a large-volume high-threshold gas Cherenkov counter (HTCC) [2] for electron identification and a tagging system to detect electrons and photons at polar angles below 5 • . The CLAS12 solenoid spans the central angular range from 35 • to 125 • and has a uniform 5 T central field.…”

The CLAS12 Forward Time-of-Flight system

“…The other detector subsystems in the forward direction are used to identify the particle type. These subsystems include the different Cherenkov counters (HTCC [4], LTCC [5], and RICH [6]), the electromagnetic calorimeters (ECAL) [7], and the FTOF. These systems are used as part of the overall CLAS12 particle identification scheme to separate the different particle species as a function of momentum.…”