Precision calibration of electromagnetic calorimeters with a radio-frequency quadrupole accelerator

Over the last six years, Caltech and AccSys Technology, Inc . have developed fast calibration techniques by using a pulsed proton beam from a radio-frequency quadrupole (RFQ) accelerator. The RFQ beam bombards a lithium (Li) or calcium fluoride (CaF2) target permanently installed in an experiment . Radiative capture of the proton yields a flux of single 17 .6 MeV photons from a Li target or short bursts of thousands of 6 MeV photons from a CaF2 target, which simulate a high energy photon of up to 40 GeV per calorimeter cell . This pulsed photon source can be used to calibrate thousands of crystals in the experiment with an absolute accuracy of 0.7% in a few hours or with a relative accuracy of 0.4% m a few minutes, using the two types of targets .