Forward Tagger Simulations New geometry Moller Shield Acceptance Background rates and dose R. De Vita INFN –Genova Forward Tagger Meeting, CLAS12 Workshop, November 10 2010

New Geometry FT support material changed to tungsten to improve radiation containment Outer case added Inner beamline modified to shield small angle crystals from beam halo 408 crystals 15x15x200 mm size Coverage from 1.8 to 5.2 deg. Tungsten beam pipe to shield from beam halo tungsten case crystals beamline to torus shield for inner crystals back flange

GEANT4 Simulations

Moller Electrons and Beam Halo The Moller shield was designed studying the transverse size of the beam halo and the Moller electrons distribution The moller spot is always larger than the size of a 2 deg cone A 2.5 deg. cone can contain most of the background Optimal z of the cone entrance is at 75 cm from the target z=50 cm z=75 cm All particles Electrons Moller electrons Moller electrons E>200 MeV Photons Others The lines indicate the size of a cone with 2 deg. and 2.5 deg. aperture z=100 cm

DC Occupancy: test of standard CLAS12 shield geometry To check reliability of the DC occupancy estimate, the standard CLAS12 Moller shield geometry (optimized by A. Vlassov) was implemented in GEMC The shield consists of an aluminum/tungsten cone with max. angle of ≈4 deg. Most of the background hitting the DC consist of photon coming from the target region Typical occupancies are of the order of 1%

DC Occupancy: FT Moller shield A shield compatible with the FT geometry and acceptance was designed based on a single tungsten cone entrance at z=75 cm outer angle: 2.45 deg inner diameter: 60 mm DC Occupancy is <2.5% in R1 and <1% in R2,R3 Improvement is possible with further optimization of the Moller shield

Electron detection and acceptance Electrons in the energy range 0.5-4.5 GeV and angular range 1-35 deg. were simulated to study the characteristic of the signal induced in the calorimeter and check the acceptance

Background Rates Background on the calorimeter due to the beam was simulated generating electrons 10 cm upstream to the target the energy deposited per ns is <0.3 MeV the particles with =0.5-4.5 GeV hitting the FT are a mix of electrons, photons and hadrons the overall rate is of about 48 MHz the rate of particles with E=0.5-4.5 GeV is ≈180 KHz

Radiation Dose The corresponding dose on the single crystals is less than 5 rad/h and less than 2 rad/h excluding the innermost crystals (not necessary for detection of electron above 2.5 deg) This dose is compatible with the operation of LeadTungsten withour significant deterioration of light transmission properties

Work Plan for Proposal and Beyond For the proposal: repeat background rates evaluation using cluster algorithm complete study of signal/background separation Long term plan: continue optimization of Moller shield and FT geometry complete implementation of calorimeter reconstruction (cluster algorithm …