Beam In HCANA.pdf

The beam apparatus used in Hall C data analysis is THcRasteredBeam and the beam detector is THcRaster. The beam object is created with a name, such as "H.rb", and can be used in physics modules. The Hall C raster consists of two sets of X and Y coils, labeled as "A" and "B", which provide information on the beam positions and direction. The raster voltage is proportional to the magnetic field in the raster coils and is used to calculate the relative beam position. The EPICS data is used to provide the average beam position, assuming a small variation over the course of a run. The THcRaster.cxx code reads in the raster current data and converts the raw raster ADC and EPICS BPM data into calibrated positions. The raster position is calculated using the relative raster position formula, which involves parameters such as the scale factor and beam energy. The BPM positions at the target can be set as parameters or determined from the EPICS data throughout the run. The BPMs are calibrated relative to the HARPs using a script that fits a group of HARP scans to determine the calibration constants. The calibrated BPM positions and angles are calculated using the BPM calibration parameters and are stored in the output tree.