Improvement of cosmic-ray proton measurement with the electromagnetic calorimeter of the Alpha Magnetic Spectrometer

Purpose The energy response of protons measured by electromagnetic calorimeter (ECAL) of Alpha Magnetic Spectrometer (AMS-02) shows disagreement between Monte Carlo (MC) simulation and data. Therefore, using the response matrix from MC to apply the energy unfolding, which is crucial for cosmic-ray proton spectrum measurement, is unreliable. As a result, cosmic-ray proton spectrum measured by ECAL based on raw MC would be different from the published results (based on the momentum measurement) by AMS-02. The purpose is tuning the response matrix to agree with data. Methods The independent energy measurement by AMS-02 magnetic spectrometer provides in-flight calibration for ECAL. The distributions of proton energy measured by ECAL in MC are corrected after the calibration. Results The proton spectrum based on the tuned response matrix is consistent with the published one. Conclusions The matrix tuning is effective for the energy unfolding for cosmic-ray proton spectrum measurement.