End-to-end absolute energy calibration of atmospheric fluorescence telescopes by an electron linear accelerator

The Telescope Array (TA) is a hybrid detector composed of atmospheric fluorescence telescopes and a ground array of particle detectors for the precise energy measurement of ultra high-energy cosmic rays. We propose an end-to-end absolute energy calibration of fluorescence telescopes by using air showers induced by electron beams from a linear accelerator, which will be installed at the site of the TA experiment and will have a well-measured beam energy. We have simulated electron beam dynamics and interaction of electrons in air to evaluate the accuracy of the beam energy determination, beam currents, air showers, and detector response using a beam simulation code (PARMELA) and GEANT4. We found that the systematic error of energy measurement estimated for the TA fluorescence telescopes can be reduced from 23% to 17% by this end-to-end energy calibration. We are developing and constructing a compact linear accelerator with a maximum electron energy of 40 MeV and an intensity of 6.4 mJ/pulse. In this article, we describe the method of absolute energy calibration and the design of the accelerator.