On-orbit equalization of the electromagnetic calorimeter of the Alpha Magnetic Spectrometer

Purpose The Alpha Magnetic Spectrometer (AMS-02) will continuously collect data for the lifetime of the International Space Station (ISS). On-orbit equalization must be performed to ensure the accuracy of the AMS energy measurement (~1%) by the electromagnetic calorimeter (ECAL).
Methods The equalization is performed using the most probable value (MPV) of the cosmic-ray proton minimum ionizing particle (MIP). Kalman filter technique is used to improve the precision.
Results The precision of the equalization with proton MIP is (7.206 ± 0.003)% and improved to (2.388 ± 0.002)% after the Kalman filter. From the toy Monte Carlo (MC) simulation, the error of the energy reconstruction is about 1.4% and 0.5% due to the 7.2% and 2.4% equalization accuracy, respectively.
Conclusion About 1.4% error due to ~7% equalization precision does not match the AMS requirement. With the improvement from the Kalman filter, the energy reconstruction error from the equalization is reduced to 0.5%, which can fulfill the AMS requirement.