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.
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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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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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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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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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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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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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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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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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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