GEANT SIMULATIONS OF PRESHOWER CALORIMETER FOR CLAS12 UPGRADE OF THE FORWARD ELECTROMAGNETIC CALORIMETER

Hall B at the Thomas Jefferson National Accelerator Facility uses the CEBAF (Continuous Electron Beam Accelerator Facility) Large Acceptance Spectrometer (CLAS) to study the structure of the nucleon. An upgrade from a 6 GeV beam to a 12GeV beam is currently planned. With the beam energy upgrade, more high-energy pions will be created from the interaction of the beam and the target. Above 6GeV, the angle between the two-decay photons of high-energy pions becomes too small for the current electromagnetic calorimeter (EC) of CLAS to differentiate between two photon clusters and single photon events. Thus, a preshower calorimeter will be added in front of the EC to enable fi ner granularity and ensure better cluster separation for all CLAS experiments at higher energies. In order to optimize cost without compromising the calorimeter’s performance, three versions of the preshower, varying in number of scintillator and lead layers, were compared by their resolution and effi ciency. Using GSIM, a GEANT detector simulation program for CLAS, the passage of neutral pions and single photons through CLAS and the new preshower calorimeter (CLAS12 EC) was studied. The resolution of the CLAS12 EC was calculated from the Gaussian fi t of the sampling fraction, themore » energy CLAS12 EC detected over the Monte Carlo simulated energy. The single photon detection effi ciency was determined from the energy and position of the photon hits. The fractional energy resolution measured was ΔE/E = 0.0972 in the fi ve-module version, 0.111 in the four-module version, and 0.149 in the three-module version. Both the fi ve- and four-module versions had 99% single photon detection effi ciency above 0.5GeV while the 3 module version had 99% effi ciency above 1.5GeV. Based on these results, the suggested preshower confi guration is the four-module version containing twelve layers of scintillator and fi fteen layers of lead. This version provides a reasonable balance of resolution, effi ciency, and cost. Additional GSIM simulations will be undertaken to verify that the four-module version has acceptable π° mass reconstruction and to continue Research and Development (R&D) analysis on the preshower calorimeter.« less