Equalization for the low-response cells of the AMS-02 electromagnetic calorimeter

Purpose Performing precision equalization on the low-response detection units of electromagnetic calorimeter(ECAL),it is essential for precision energy measurements of Alpha Magnetic Spectrometer(AMS-02).Methods Cosmic helium nuclei are used instead of protons to perform the equalization.During the equalization,temperature effects are analyzed and corrected to improve the accuracy.Results The results of helium equalization are consistent with proton equalization,and the precision of helium equalization is about 1.5%.Conclusions The precision of helium equalization is better than that of proton equalization,which provides a reliable alternative to ECAL on-orbit equalization.

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.

Cosmic-ray helium nuclei measurement with the calorimeter of the Alpha Magnetic Spectrometer

Purpose The distributions of energy responses of helium measured by the electromagnetic calorimeter(ECAL)of Alpha Magnetic Spectrometer(AMS-02)in Monte-Carlo do not agree with those in real data,thus using energy response matrix obtained from Monte-Carlo to measure the cosmic ray helium spectrum is not correct.Therefore,the spectrum measured with ECAL based on raw Monte-Carlo would be different from the real one.The purpose is to correct the response matrix to measure helium spectrum with ECAL.Methods The energy measured by ECAL of AMS-02 provides in-flight correction for the energy response matrix in Monte-Carlo.Results The spectrum based on corrected response matrix is consistent with the AMS collaboration published result.Conclusions It is feasible to measure helium spectrum with ECAL with corrected energy response matrix.

Improvements on the particle identification with dead cell and side leakage corrections for the electromagnetic calorimeter of the Alpha Magnetic Spectrometer

Background The electromagnetic calorimeter(ECAL)of the Alpha Magnetic Spectrometer(AMS-02)measures the energy of electrons/positrons and separates them from protons.Currently,there are five dead cells in the ECAL which affect the reconstructed energy of particles.The particle identification power of the ECAL decreases when particles pass through these dead cells or close to the ECAL border.Purpose To improve the ECAL particle identification for particles pass through these dead cells or close to the ECAL border.Methods An improved ECAL particle identification estimator using the electromagnetic shower shape is developed with dead cell and side leakage corrections.Results For events passing through dead cells,with this new estimator,the proton rejection power is improved by a factor of 2.2 and positron purity is improved from 31 to 50%in the energy range of 500–800 GeV.Conclusion The new estimator works well for event passing through dead cells or close to the ECAL border.

Improvement of cosmic-ray protonmeasurement 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.

Improvement in the 3D shower shapes description in the Monte Carlo simulation for a lead-scintillating fiber electromagnetic calorimeter

Background The lead-scintillating fiber electromagnetic calorimeter(ECAL)of the Alpha Magnetic Spectrometer measures the energy of positrons/electrons and separates them from hadrons.The electromagnetic shower shapes from Monte Carlo(MC)simulation and data show disagreement.Purpose Tuning the MC to make the shower shapes from MC and data agree with each other.Methods The tuning is based on a 3D electromagnetic shower model.Results After tuning,the electromagnetic shower shapes are well described by MC up to TeV.As a result,the output of ECAL electron/proton separation estimator,ECAL BDT,shows thatMCand data are in good agreement.The proton rejection power of the ECAL BDT trained with MC electron samples is improved by a factor of 5 at∼800 GeV compared to the one trained with data.