In AMS, for all Z, the largest systematic error in the determination of the fluxes at the highest energies is due to the uncertainty of the absolute rigidity scale. The AMS tracker was aligned using the CERN SPS test beam.
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In the page we present the improvements in the data analysis, which made possible accurate measurements of electrons and positrons in the TeV energy range and precision measurements of the cosmic ray nuclei fluxes of Li, Be, B, C, N, and O. These improvements will also enable us to collect data at much higher energies for electrons and positrons and nuclei up to Z=30.
Improvements in the Tracker Analysis
Track Finding Efficiency Improvements in the Tracker Analysis
We have improved the track finding algorithm. The new algorithm uses cellular automation for finding the track segments and then builds the tracks, as illustrated in Figure 1. This improves track finding efficiency and rejection of spurious hits in the detector.
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Improvement in the Rigidity Resolution at Low Rigidities with the New Track Fitting Algorithm
At low rigidities (<10 GV), we have implemented a new track fitting algorithm based on the Kalman filtering technique. It more accurately accounts for energy losses and multiple scattering by charged particles, see C. Höppner, S. Neubert, B. Ketzer, and S. Paul, Nuclear Inst. and Methods in Phys. Res., Sect.
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Improvements in the Charge Resolution
The nine tracker layers independently measure the charge $|Z|$ of cosmic rays. The ionization energy losses deposited in the silicon, see Figure 1, are proportional to $Z^{2}$ and this is measured with both the x- and y- side strips.
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Charge Sign Identification Improvement in the Tracker Analysis
Test beam data are crucial in understanding the detector performance details. Figure 1 shows the comparison between data and the Monte Carlo simulation of the inverse rigidity measured by the tracker for 400 GeV/c test beam protons.
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Tracker Coordinate Measurement Improvement in the Tracker Analysis
The y coordinate provides better accuracy by design, in which the readout strips have much smaller pitch compared to the strip pitch in the x coordinate. We present the improvement in the accuracy of determination of y-coordinate, which is the most important for the determination of momentum (or rigidity).
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Improvements in the ECAL Analysis
Improvements in the proton rejection using ECAL
We have improved the identification of electrons and positrons in the TeV energy range. This is achieved by increasing the proton rejection with an ECAL estimator $\Lambda_\text{ECAL}$. The estimator is constructed based on the information from the new ECAL reconstruction described above.
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New Reconstruction Method in the Electromagnetic Calorimeter (ECAL) Analysis
The key detector for measurements of electrons and positrons in AMS is the Electromagnetic Calorimeter, ECAL (see Figure 1). The ECAL consists of a multilayer sandwich of lead foils and ∼50,000 scintillating fibers with an active area of 648 × 648 mm2 and a thickness of 166.5 mm, corresponding to 17 radiation lengths, $X_0$.
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Improvement in the ECAL Energy Reconstruction
The signal saturation in the electronics is insignificant over the energy range of interest, the remaining saturation is in the calorimeter fibers. It is related to conversion of ionization to light. As illustrated in Figure 1 the effect is maximal near the shower peak, whereas for the rest of the shower, the cells are not affected.
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Measurements
Measurements of Nuclei Cross Sections with cosmic rays
To accurately measure the fluxes of cosmic-ray nuclei we need to know the interaction cross sections of these nuclei with the thin material within AMS. The material is composed mostly of carbon (73%) and aluminum (17%). The corresponding inelastic cross sections have only been measured below 10 GV for He and C and have not been measured for other nuclei.
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