Precision Measurement of the $(e^{+}+e^{-})$ Flux in Primary Cosmic Rays from 0.5 GeV to 1 TeV with the Alpha Magnetic Spectrometer on the International Space Station

We present a measurement of the cosmic ray $(e^{+}+e^{-})$ flux in the range 0.5 GeV to 1 TeV based on the analysis of 10.6 million $(e^{+}+e^{-})$ events collected by AMS. The statistics and the resolution of AMS provide a precision measurement of the flux. The flux is smooth and reveals new and distinct information. Above 30.2 GeV, the flux can be described by a single power law with a spectral index $\gamma =-3.170\pm 0.008(\text{stat}+\text{syst})\pm 0.008(\text{energy}\text{scale})$.

Figure 1

The result of the template fit in the 149–170 GeV bin showing the small proton background overlapping the $(e^{+}+e^{-})$ signal. The fit has a ${\chi }^2/d.f.=0.55$.

Figure 2

For the 500–700 GeV bin: (a) $N_E$ versus ${\epsilon }_{\text{ECAL}}$ for the 2000 trials showing that the result is stable over a wide range of ${\epsilon }_{\text{ECAL}}$. The scale on the right indicates the number of trials. (b) The distribution of $N_E$ for the 2000 trials. The narrow width (a rms of 4%) of the distribution indicates the accuracy at the highest energies.

Figure 3

The flux of electrons plus positrons $\mathrm{\Phi }(e^{+}+e^{-})$ measured by AMS multiplied by ${\tilde{E}}^3$ versus energy. The AMS error bars are the quadratic sum of the statistical and systematic errors. Also shown are the results from earlier experiments [11, 12, 13, 14, 15, 16, 17].

Figure 4

(a) The spectral index of $\mathrm{\Phi }(e^{+}+e^{-})$ as a function of energy. The shaded regions indicate the 68% C.L. intervals including the correlation between neighboring points due to the sliding energy window. (b) $\mathrm{\Phi }(e^{+}+e^{-})$ multiplied by ${\tilde{E}}^3$ versus energy and the result of a single power law fit above 30.2 GeV.